Next Article in Journal
Experimental Study on Fatigue Performance of CRTS III Ballastless Track-Girder System Considering Transverse Wheel–Rail Force
Previous Article in Journal
Correlations Between Crystallinity, Rheological Behavior, and Short-Term Biodegradation for LDPE/Cellulose Composites with Potential as Packaging Films
Previous Article in Special Issue
Selective CO2 Detection at Room Temperature with Polyaniline/SnO2 Nanowire Composites
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Coatings
Volume 15
Issue 4
10.3390/coatings15040398
coatings-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Low Molar Mass Carbazole-Based Host Materials for Phosphorescent Organic Light-Emitting Diodes: A Review

by
Gintare Krucaite
* and
Saulius Grigalevicius
*
Department of Polymers Chemistry and Technology, Kaunas University of Technology, Radvilenu Plentas 19, LT50254 Kaunas, Lithuania
*
Authors to whom correspondence should be addressed.
Coatings 2025, 15(4), 398; https://doi.org/10.3390/coatings15040398
Submission received: 20 February 2025 / Revised: 19 March 2025 / Accepted: 24 March 2025 / Published: 27 March 2025
(This article belongs to the Special Issue Advanced Nanomaterials and Coating Technologies for High-Performance Electronic, Optoelectronic, Energy, and Sensing Devices)
Browse Figures
Versions Notes

Abstract

:
The second-generation phosphorescent organic light-emitting diodes are formed using phosphorescent emitters, which can theoretically achieve 100% internal quantum efficiency. However, these emitting materials usually suffer from triplet–triplet annihilation (TTA) and/or concentration-quenching effects. To address the disadvantages, host–guest systems are used in the emitting layer, where the guest is dispersed into a host matrix. Carbazole is one of the most commonly used electron-donating fragments, which is widely applied as a building block for the synthesis of the mentioned host materials. In this review article, we describe the synthesis, thermal, electrochemical, and optoelectronic properties of the hosts with carbazolyl units as well as application of the matrixes in the phosphorescent devices. This review is written from the perspective of structural chemistry and the host materials are divided in several groups as 9-arylcarbazoles, twin derivatives containing two carbazolyl fragments, 3(2)-aryl(arylamino)-substituted, and 3,6(2,7)-diaryl(diarylamino)-substituted carbazoles.

1. Introduction

After the invention of the first OLED constructed using organic materials as an emitting element about 38 years ago [1], the technology has undergone tremendous progress. When properly stacked, the organic materials result in devices with suitable efficiency and lifetime. The OLEDs become attractive due to their lower formation cost, light weight, better contrast ratio, and transparency as compared with analogue inorganic devices [2,3,4,5,6]. The red, green, and blue devices can be combined in matrices to become the core of displays [7,8]. Since Baldo et al. have reported phosphorescent organic light-emitting devices (PhOLEDs), they have been attracting much attention because of their potential use in general illumination and flat panel displays [9,10]. The PhOLED devices are formed on glass with the configuration of indium-tin-oxide (ITO) anodes, hole-transporting layers, emitting layers, electron-transporting layers, and metal (like Al or LiF) cathodes. Compared to others, the phosphorescent devices are fabricated by doping host materials, with high-energy triplet states with phosphorescent guest materials (emitters), and can theoretically produce 100% internal quantum efficiency (IQE). This is achieved by utilization of both singlet and triplet excitons in the light-emission process [11,12,13,14]. However, the relatively long lifetime of the phosphorescent material may lead to dominant triplet–triplet annihilation at high currents and may also cause a long range of exciton diffusion that could be quenched in adjacent layers of the OLEDs [15]. For an efficient energy-transfer process, holes and electrons should be recombined in a host material and exciton energy of the host should be transferred to phosphorescent emitters [16]. For an efficient energy transfer in PhOLED, a host material must ensure that triplet energy of the host is higher compared to the emitter to prevent reverse energy transfer from the emitter back to the host and to confine triplet excitons effectively on the emitter molecules [17,18,19,20,21]. An application of host materials consisting of donor and acceptor units proved successful, owing to their balanced charge transport properties and thus simplified device structures [22,23,24]. For this purpose, researchers are synthesizing new organic bipolar hosts containing carbazole, fluorene, triphenylphosphine, benzonitrile, ketone, carboline, pyridine, diphenylamine, benzimidazole, and other fragments [25,26,27,28,29,30,31,32]. The most efficient are the bipolar hosts constructed on the “donor-acceptor” molecular design and with carbazole rings as electron donating fragments [33,34,35,36]. The structure of the 9H-carbazole molecule is shown in Figure 1. Nitrogen atoms in the 9H-carbazole ring can be modified with various substituents (e.g., alkyl, aryl, or acyl groups) to form N-alkylcarbazoles, N-arylcarbazoles, and N-acylcarbazoles. The carbazole can be oxidized or reduced. Through standard organic synthesis reactions like Ullmann, Suzuki–Miyaura, Suzuki, Mannich, Miyaura, or Buchwald–Hartwig, different electron-accepting groups at specific positions on the carbazole ring can be added in order to form conjugated and/or bipolar host materials. Thermal stability of the carbazole-based derivatives can be increased by the substitution of the ring with rigid aromatic structures. On the other hand, the molecular weight of the derivatives should be increased so that the materials cannot evaporate thermally at low temperatures in TGA experiments. The values of LUMO and HOMO energies of the reviewed bipolar derivatives can be controlled by attaching acceptor fragments with different electron-accepting properties and/or a different number of the mentioned units to the carbazole core. An acceptor usually increases the values of HOMO–LUMO; however, this also depends on the interaction between donor and acceptor fragments in the bipolar derivatives. It should be mentioned that the bipolar host derivatives should have the suitable LUMO–HOMO values in order to be used for red, green, or blue phosphorescent emitters. Firstly, the HOMO of the host material should be aligned with that of the hole-transport material for good hole injection, while the LUMO of the host material should be aligned with that of the electron-transport material for good electron injection. Additionally, the HOMO and LUMO level mismatch between the host and emitter materials needs to be minimized for efficient light emission, because the energy level mismatch hinders exciton formation in both the host and emitter materials. Furthermore, the HOMO–LUMO gap between host and emitter materials needs to be well adjusted because the contribution of each light-emission mechanism to the whole light-emission process is determined by the HOMO–LUMO gap [37].
In this review, we summarize carbazole-based host materials used in the PhOLEDs over the past years. The carbazole ring has several reactive positions and due to this, several different groups of the derivatives can be developed, i.e., bipolar donor-acceptor (D-A) 9-arylcarbazoles, twin derivatives containing two carbazolyl fragments, 3 or 2-aryl(arylamino)-substituted derivatives as well as 3,6 or 2,7-diaryl(diarylamino)-substituted carbazoles. The materials are grouped according to the mentioned structural features in this review. Synthesis, thermal, and electrochemical properties as well as the application of the different groups of carbazoles in PhOLEDs were reviewed. The results are of significant interest for the development of high-performance devices. Understanding the structure–properties relationships enables the rational design of new host materials with optimized characteristics for the specific role within the PhOLEDs.

2. 9-Aryl Substituted Carbazoles

Several groups of low molar mass 9-aryl-substituted carbazole-based compounds were investigated and reported in the literature. Structures of the bipolar compounds A1–A31 with thiophene, benzenesulfonamide, pyrrole, phthalonitrile, carbonitrile, cyanophenyl, pyridine, isoquinoline, benzoimidazole, benzoquinoline, bispyridyl-tiazole, or pyrazolylpyridine fragment as an acceptor are demonstrated in Scheme 1. 9-(4-(2-thiophene)phenyl)carbazole (A1) was synthesized by Ullmann reaction of 9H-carbazole and dibromobenzene in a first step, then the received 9-(4-bromophenyl)carbazole reacted with 2-thiopheneboronic acid to yield the final compound [38]. The condensation reaction of 4-(9H-carbazol-9-yl)benzaldehyde with 2-amino benzenesulfonamide in the presence of sodium bisulphite resulted in the formation of A2 [39]. 5-(9H-carbazol-9-yl)picolinaldehyde on reaction with 1-(2-aminophenyl)pyrrole in presence of FeCl3 offered compound A3. Similarly, 5-(9H-carbazol-9-yl)picolinaldehyde on reaction with 2-aminobenzenesulfonamide in presence of sodium hydrogen sulphate yielded A4 [40]. 4-(9H-carbazol-9-yl)phthalonitrile (A5) was easily prepared by a one-step aromatic nucleophilic substitution reaction between 9H-carbazole and 4-fluorophthalonitrile [41]. 5-(9H-carbazol-9-yl)indolo [3,2,1-jk]carbazole-2-carbonitrile (A6) was obtained when 5-iodoindolo [3,2,1-jk]carbazole-2-carbonitrile reacted with 9H-carbazole [42]. The synthesis of target compounds A7 and A8 was accomplished by the Pd-catalyzed Suzuki–Miyaura coupling reaction of the 9-(2-bromophenyl)carbazole or 9-(2,6-dibromophenyl)carbazole with (4-cyanophenyl)boronic acid [43]. The target compound A9 was prepared in a simple one-step cross-coupling reaction of 9H-carbazole and 2,6-diphenyl-4-bromobenzonitrile [44].
The host material 4-{3-[4-(9H-carbazol-9-yl)phenyl]adamantan-1-yl}benzonitrile (A10) was synthesized by two reactions. An intermediate was prepared by the Ullmann coupling reaction between the iodo-substituted adamantine precursor and carbazole. Then, the remaining iodo-group was replaced by cyano group to provide the desired product A10 [45]. Suzuki cross-coupling reaction of 9-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)carbazole with 2-bromo-6-methylpyridine or 1-chloroisoquinoline produced A11 and A12, respectively. Compound A13 was prepared by the Buchwald-Hartwig cross-coupling of 2-bromo-6-phenylpyridine with 9H-carbazole [46].
Compound A14 was synthesized by Ullmann reaction of bromoindolecarbazole and 9H-carbazole, while compound A15 was obtained by Suzuki cross-coupling reaction of the bromoindolecarbazole and 4-(carbazol-9-yl)phenyl boronic acid pinacol ester [47]. Carbazole-benzimidazole bipolar host material A16 was synthesized by Ullmann reaction of 1-(3-bromophenyl)-2-phenyl-1H-benzo[d]imidazole and 9H-carbazole [48,49]. Materials A17-A19 were synthesized by Ullmann reaction of 9-(3-bromophenyl)carbazole, 9-(3,5-dibromophenyl)carbazole, or 9,9′-(5-bromo-1,3-phenylene)bis(9H-carbazole) with 2,2′-di(2-pyridyl)amine [50]. Compound A20 was obtained in Buchwald–Hartwig reaction of 9-[3,5-di(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl]phenyl)carbazole and 9-bromobenzo[f]quinoline [51]. Two substituted 9-phenylcarbazole derivatives A21 and A22 were synthesized using Ullmann coupling reaction between p- or m-phenylcarbazole and 3,5-bis(2-pyridyl)-1H-1,2,4-tiazole [52].
Compounds A23–A26 were obtained through nucleophilic substitution of cyanuric chloride in two steps. In the first step, the mono- and diaryl-substituted triazines were prepared by using a Grignard reaction and nucleophilic substitution. In the second step, a catalyzed nucleophilic substitution of the intermediate cyanuric chloride with lithium carbazole resulted in the desired compounds [53]. Compounds A27–A28 were prepared by Suzuki cross-coupling reaction between carbazole-containing boronic acids and brominated n-type units [54]. Three isomers A29–A31 were synthesized in a simple and easy procedure. Firstly, an intermediate 2-bromo-5-(pyrazol-1yl)pyridine was prepared by coupling pyrazole and 2-bromo-5-iodopyridine under Ullmann condensation conditions. Then, the target compounds A29–A31 were prepared through the Suzuki cross-coupling reaction between the intermediate and corresponding boronic acid of 9-phenylcarbazole [55].
Properties of the compounds A1–A31 are presented in Table 1. Thermal stability of all the derivatives A1–A31 was investigated by thermogravimetric analysis (TGA). The thermal decomposition temperatures (Td) corresponding to 5% weight loss were observed ranging from 271 °C to 509 °C, indicating good thermal stability of these compounds. Glass transition temperatures (Tg) of the materials were obtained by differential scanning calorimetry (DSC) and ranged from 49 °C to 187 °C. Electrochemical measurements using cyclic voltammetry were used to analyze oxidation and reduction potentials of the host materials A1–A31. Energy values of LUMO and HOMO were calculated from the onset potentials of electrochemical reduction and oxidation. The HOMO levels of compounds A1–A31 were mostly dispersed over the carbazole unit and were very close to 6 eV, while LUMO ranged from 2.08 eV to 3.13 eV and depend on chemical structures of substitutes. Phosphorescent emission of the materials A1–A31 was observed in their low temperature PL spectra and triplet energies (Et) are calculated from the first phosphorescence emission peak. The triplet energies of the compounds A1–A31 are very different because they have various substituents in their structures.
The hosts A1–A31 were used in formation of the PhOLEDs. The structures and properties of the devices are presented in Table 1. It can be seen that the devices using the host materials A1–A31 have different current efficiencies (CE), power efficiencies (PE), and external quantum efficiencies (EQE). The blue device with host A16 exhibited CEmax of 54.5 cd/A, PEmax of 52.2 lm/W, and a maximum EQE of 26.2%. These characteristics are better than those of many other blue light-emitting devices described in the literature. Blue and green light devices with hosts A27 or A28 using FIrpic or Ir(ppy)3 as emitting guests were investigated by F. Wang and co-workers. PhOLED with A27 as a host exhibited a turn-on voltage (Von) of 2.7 V with moderate EQE of 28%. T. Zhang et al. investigated materials A29 and A31 [56] and obtained similar data to other researchers. The A29-based green device achieved a high efficiency of 29.08% (96.98 cd/A), which is among the highest values for PhOLEDs with Ir(ppy)3 dopant ever reported in the public scientific literature.
Another group of low molar mass 9-aryl-substituted carbazole-based bipolar compounds B1–B24 with thiophenyl, diphenylphosphine, diphenylphosphoryl oxide, triazolyl, diphenylphosphine, diphenylphosphine oxide, phenylbenzimidazole, triazine, benzofuropyrimidine, or spironaphthalenone fragment as an acceptor is demonstrated in Scheme 2. Compound B1 was prepared then 9-[4-(thiophen-2-yl)phenyl]carbazole was reacted with n-BuLi, followed by the addition of chlorodiphenylphosphine [57]. While compound B2 was prepared, 9-(benzo[b]thiophen-5-yl)carbazole reacted with n-BuLi, followed by the addition of chlorodiphenylphosphine [58]. A host compound B3, incorporating carbazole and diphenylphosphoryl oxide moieties as electron-donating and accepting groups, was synthesized then 2-(4-bromophenyl)-1-[4-(diphenylphosphoryl)phenyl]benzo[d]imidazole reacted with 9H-carbazole [59]. Compound B4 was prepared by reacting 9-(3-(5-(4-bromophenyl)-4-phenyl-4H-1,2,4-triazol-3-yl)phenyl)carbazole with n-BuLi, followed by an addition of chlorodiphenylphosphine [60]. Derivative B5 was synthesized via Ullmann reaction of 9H-carbazole with 2-bromo-2′-(diphenyloxophosphinoyl)biphenyl [61]. Host material B6 was obtained by a Suzuki-coupling reaction when 9-[3-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]carbazole reacted with (4-bromo-3-methylphenyl)diphenylphosphine oxide [62]. Compound B7 was prepared via the CP coupling reaction between 9-{4-[1-(4-iodophenyl)cyclohexyl]phenyl}carbazole and diphenylphosphine oxide. The synthesis of B8 was then accomplished by treating B7 with Lawesson’s reagent [63]. In situ reaction of mono-substituted 9-[4-(chlorodimethylsilyl)phenyl]carbazole with [4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]lithium produced the final product B9 [64]. C-N coupling reaction of 2-{4-[(4-bromophenyl)(diphenyl)silyl]phenyl}-1-phenylbenzimidazole or 2-{3-[(3-bromophenyl)(diphenyl)silyl]phenyl}-1-phenylbenzimidazole with 9H-carbazole produced the objective products B10 and B11 [65]. Bipolar hosts B12 and B13 were received from the two key intermediates, CN modified tetraphenylsilyl unit and carbazole modified triazine unit, which were separately prepared and then coupled in the final step to produce the two hosts [66]. Compound B14 was obtained when the tetraphenylsilyl group was attached through Suzuki–Miyaura coupling reaction to the 2 position of benzo [4,5]furo[3,2-d]pyrimidine using dioxaborolane-functionalized tetraphenylsilane [67]. Compound B15 connecting the N-carbazolyl unit and phenylsulfonyl group was synthesized by Pd-catalyzed Suzuki coupling reaction of 4,4,5,5-tetramethyl-2-[2-methyl-4-(phenylsulfonyl)phenyl]-1,3,2-dioxaborolane with 9-(4-bromo-3-methylphenyl)carbazole [68]. Target derivatives B16–B18 were obtained by Suzuki reaction of 6-bromo-2,3-diphenylquinoxaline with (4-(9-carbazol)phenyl)boronic acid or by reaction of 2,3-diphenyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinoxaline with corresponding 9-(2- or 3-bromophenyl)carbazole [69]. The target compound B19 was obtained by the Suzuki cross-coupling reaction of 2-(4-bromophenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole with 9-(4′-bromo-2′,5′-dimethyl-[1,1′-biphenyl]-4-yl)-9H-carbazole [70]. Compounds B20–B22 were prepared by Suzuki cross-coupling reaction when 2-(3-bromo-5-chlorophenyl)-1-phenyl-1H-benzo[d]imidazole reacted with different 3′-chloro-5′-(1-phenyl-1H-benzo[d]imidazole-2-yl)-[1,1′-biphenyl]- carbonitriles [71]. The Suzuki cross-coupling reaction of 4,4,5,5-tetramethyl-2-[1,1′:3′,1′-terphenyl]-5′-yl-1,3,2-dioxaborolane with 9-(3,5-dibromophenyl)carbazole led to compound B23 [72]. Reaction of bromine substituted spironaphthalenone with [4-(9-carbazolyl)phenyl]boronic acid under Pd(PPh3)4 catalyst delivered the target host material B24 [73].
Properties of the compounds B1–B24 are presented in Table 2. The host materials depicted favourable Td, which range from 315 °C to 454 °C, indicating that they can endure with vacuum deposition and fulfill the demand of the hosts to be adopted in the device. The Tg of compounds B3–B24 were estimated to be higher than 72 °C according to the DSC tests. The reported HOMO and LUMO energy levels of derivatives B1–B24 were different and depended on aryl substituents connected to carbazole core. The levels of these compounds were in the range 5.41–6.15 eV for HOMO and 1.78–2.82 eV for LUMO. The Et energies of these compounds range from 2.37 eV to 3.06 eV. In virtue of the higher triplet energy levels, some of the materials can be considered as the suitable host compounds for blue and red phosphors.
The structures and efficiencies of the devices with hosts B1–B24 are presented in Table 2. The suitable thermal stabilities and photo-physical properties allowed for the compounds to be used as universal hosts for PhOLEDs. The described devices achieved EQE that ranged from 9.2% to 31.8%.
A blue OLED hosted by B15 achieved an excellent EQE of 31.8% with low turn-on voltage. Bipolar host material B8 with green 4CzIPN emitter reached EQE of 21.7% at a high luminance of 100 cd/m2. Employing B24 as host material in red OLED achieved high EQE of 16.6%.
Group of low molar mass 9-aryl-substituted carbazole-based compounds C1–C33 containing benzothiophene, dibenzofuran, fluorenone, phenothiazine-5,5-dioxide, or carboline electron accepting substituents is shown in Scheme 3. Synthesis of the materials C1 and C2 began with 9H-carbazole witch was N-arylated with 4-bromobenzaldehyde using Ullmann coupling reaction to give 4-(9-carbazolyl)benzaldehyde that was subsequently treated with 9-ethylcarbazole or 9-hexylcarbazole to form the desired materials C1 and C2 [74,75]. In the reaction of 9,9′-(5-bromo-1,3-phenylene)bis(9H)-carbazole and 2-(2,3-diphenylbenzo[b]thiophen-5-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, compound C3 was obtained [76]. The 9,9′-(4-(2,6-diphenylpyrimidin-4-yl)-1,3-phenylene)bis(9H-carbazole) (C4) was obtained when 9H-carbazole reacted with 4-(2,4-difluorophenyl)-2,6-diphenylpyrimidine [77]. Compound C5 was obtained when 9H-carbazole was reacted with 2,4,6-trifluorobenzonitrile [78]. 9-[8-(diphenylphosphoryl)dibenzo[d,b]furan-2-yl]carbazole (C6) was synthesized when 2,8-di(carbazol-9-yl)dibenzo[d,b]furan was exposed to H2O2 [79]. Compounds C7 and C8 were prepared by Suzuki–Miyaura cross-coupling reaction between different fluorenone bromides and 9-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)carbazole [80]. When 9-[3-bromo-5-(carbazol-9-yl)phenyl]pyrido[2,3-b]indole was coupled with 4-(4,4,5,5-teratmethyl-1,3,2-dioxaborolan-2-yl)dibenzothiophene by Suzuki–Miyaura coupling reaction, a desired material C9 was formed [81]. Target products C10 and C11 were synthesized by Suzuki coupling reaction when 4-(bromo-[1,2,4]triazolo[1,5-a]pyridin2-yl)phenylcarbazole or 5-(bromo-[1,2,4]triazolo[1,5-a]pyridin2-yl)phenylcarbazole reacted with 9,9′-spirobi[fluoren]-2-ylboronic acid [82]. The key intermediate step in the introduction of carbazolyl substituent into the fifth position of the spiro[fluoreno-7,9′-benzofluorene] by amination reactions was used in order to synthesize host material C12 [83]. Derivative C13 was also obtained by the Ullmann reaction of 2-bromo-spiro[fluorene-9,9′-xanthene] with 9H-carbazole [84]. Material C14 was readily synthesized by a Miyaura−Suzuki coupling between the key platform of 4-bromo-9,9′-spirobi[fluorene] and 9-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]carbazole [85]. 2-bromotriphenylamine was treated with n-BuLi followed by the addition of 3-bromofluorenone to afford a tertiary alcohol, which was converted to spiro[acridine-9,9′-fluorene]core in a next step. Finally, the host material C15 was obtained via a Buchwald−Hartwig amination reaction of the core with 9H-carbazole [86]. The Suzuki coupling reaction of 5-(5-bromopyridin-2-yl)-10,11-dihydro-5H-dibenzo[b,f]azepine and [4-(carbazol-9-yl)phenyl]boronic acid produced C16 [87]. Compounds C17 and C18 were synthesized by the Suzuki coupling of 9-(9,9-diethylfluoren-2-yl)carbazole boronic ester and 1-chloroisoquinoline or 2-chloro-3a,7a-dihydrobenzo[d]thiazole in the presence of a palladium catalyst [88].
A key starting material for C19–C22 d-carboline was synthesized according to the following steps: phenylboronic acid reacted with 2-bromo-3-nitropyridine by Suzuki–Miyaura reaction to produce 2-phenyl-3-nitropyridine, which was treated with 1,2-bis(diphenylphosphino)ethane to undergo an intra-molecular condensation. The prepared d-carboline was then treated with haloarene under Ullmann coupling conditions to yield N-(haloaryl)-d-carboline, which could react with arylboronic acids under Suzuki reaction conditions to produce target host materials C19–C22 [89,90]. Three carboline-based derivatives C23–C25 were synthesized by Ullmann coupling reaction between 9-(3-iodophenyl)carbazole and corresponding carboline derivatives [91]. Compound C26 was obtained when 9-(3′-bromo-[1,1′-biphenyl]-3-yl)carbazole reacted with 2-(3-(dibenzothiophene-4-yl) phenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, while compound C27 was obtained when 4,4′-(5-bromo-1,3-phenylene)dibenzothiophene reacted with 3-(9-carbazolyl)phenyl boronic acid [92].
Buchwald–Hartwig reaction conditions were implemented for the coupling of 9-(5-bromopyridin-2-yl)carbazole and 10-[6-(carbazol-9-yl)pyridin-3-yl]-9,9-diphenyl-9,10-dihydroacridine to obtain compound C28 [93]. An intermediate, 7-bromo-9,9-dimethylfluorene-2-bis(pinacolate)diboron, was used in the Suzuki–Miyaura cross-coupling reaction with different bromo-substituted N-phenylcarbazoles to obtain the desired host materials C29–C31 [94]. The target molecule C32 was synthesized by Suzuki coupling reaction between 2-(4-bromophenyl)-4,6-bis(9,9-dimethylfluoren-2-yl)-1,3,5-triazine and phenylcarbazole boronic acid [95]. Synthesis of compound C33 was carry out by palladium catalyst activated coupling reaction between 9-(3-bromo-[1,1′-biphenyl]-3-yl)carbazole and 9,9-dimethyl-9,10-dihydroacridine [96].
The properties of the compounds C1–C33 are presented in Table 3. The values of Td for these derivatives were higher than 304 °C. It was reported that the derivatives C1–C5, C7, C9–C10, C12–C16, C20–C22, and C26–C33 were capable of glass formation with Tg ranging from 73 to 300 °C. The materials showed triplet energies over 2.25 eV and were suitable as the host material for PhOLEDs of various colours. The HOMOs of the materials C1–C33 are mainly distributed over the electron-donating carbazole moiety and slightly extended to the phenyl ring attached to ninth position of the carbazole core. The LUMOs are mostly localized on the benzothiophene, dibenzofuran, fluorenone, phenothiazine-5,5-dioxide, or carboline substituents. Moreover, both the HOMO and LUMO of materials C1–C33 have contributions from nitrogen atoms of the carbazole core due to the supply of its lone electron pair for an extended conjugation. The HOMO and LUMO levels of compounds C1–C33 fall in the range of 5.40–6.53 eV and 1.39–3.31 eV, respectively.
To investigate the electroluminescent properties of compound as host materials different devices were fabricated. The OLED architectures of blue and green light emitting devices using FIrpic or Ir(ppy)3 as dopants in C2 host were prepared [97]. The green device showed maximal efficiency of 11.4% (39.9 cd/A and 41.8 lm/W) and low turn on voltage of 3.0V. The blue device exhibited maximum EQE of 9.4% (21.4cd/A and 21.7 lm/W) with turn on voltage of 2.9V. Deep blue OLEDs with C23–C25 hosts and FCNIrpic dopant demonstrated EQE of 24.3% for the C23-based device, 21.9% for C24, and 17.0% for C25. The high EQE of the C23-hosted device was related to its high triplet energy and bipolar charge transport properties. A device using C28 host with 6.0 wt % of t4CzIPN dopant had the best performance with the maximum EQE of 24.0%, CE of 82.2 cd/A, and PE of 46.9 lm/W. Furthermore, the EQE values of 23.1 and 21.7% were retained at high luminance levels of 500 cd/m2 and 1000 cd/m2, respectively, implying small efficiency roll-off effects of only 3.7% and 9.6%, respectively.

3. Twin Host Derivatives Containing Two Carbazolyl Fragments

Structures of the low molar mass twin compounds with two carbazole rings connected per ninth position to central core are shown in Scheme 4. The target product D1 was obtained by Buchwald–Hartwig reactions of 3,3′-sulfonylbis(iodobenzene) with 9H-carbazole [98]. D2 was facilely obtained by a one-pot nucleophilic addition reaction of the organolithium compounds formed from 9-(4-bromophenyl)carbazole and n-BuLi followed by treatment with sulphur in dichloromethane [99]. Material D3 was synthesized through a substitution reaction of 9H-carbazole with dichlorophenylphosphine and then by oxidization of the received compound with H2O2 [100]. Material D4 was effectively synthesized from a brominated mCP intermediate, which was phosphorylated with chlorodiphenylphosphine [101]. 9,9′-(6-(Diphenylphosphoryl)-1,3,5-triazine-2,4-diyl)bis(9H-carbazole) (D5) was synthesized when 9,9′-(6-chloro-1,3,5-triazine-2,4-diyl)bis(9H-carbazole) reacted with 2-chloro-4,6-diphenyl-1,3,5-triazine [102]. Compound D6 was synthesized via one step Suzuki coupling reaction between 2,6-dibromoisonicotinonitrile and 3-(carbazol-9-yl)phenylboronic acid [103]. D7 host was prepared by coupling reactions between 9,9′-(5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)1,3-phenylene)bis(9H-carbazole) and 1,3,5-tribromobenzene followed by CN substitution of the 9,9′-(3′,5′-dibromo-[1,1′biphenyl]-3,5-diyl)bis(9H-carbazole) intermediate [104]. Compound D8 was obtained then 4,5-dichlorophthalonitrile reacted with 3-(carbazol-9-yl)phenylboronic acid [105]. An adding sequence of NaH-deprotonated carbazole and 2,4,6-trichloropyrimidine was used to produce different isomeric intermediates, which were separated and utilized to make the targets D9–D10 with a final cyanation reaction [106]. Compound D11 was easily synthesized by Ullmann coupling reaction when 2,5-dibromo-1-phenylpyrrole reacted with 9H-carbazole [107].
Borylated product D12 was made in the Buchwald–Hartwig reaction when (3,5-dibromophenyl)dimesitylborane reacted with carbazole [108]. The synthesis of the materials D13 and D14 was carried out using a general Suzuki coupling reaction of 1-bromo-3,5-di(carbazol-9-yl)phenyle with a corresponding boronic acid [109]. Host D15 was synthesized by a Pt catalyst-mediated coupling reaction between carbazole and 2-(3,5-dichlorophenyl)-3-methylpyridine [110]. Two different [1,2,4]-triazolo-[1,5-a]pyridine-based host materials (D16 and D17) were synthesized when the intermediates 2,6- or 3,5-di(9H-carbazol-9-yl)benzonitrile reacted with 2-aminopyridines [111]. The nucleophilic aromatic substitution of 2-(2,6-difluorophenyl)-1-phenylbenzo[d]imidazole with 9H-carbazole produced compound D18 [112]. Compounds D19 and D20, containing benzimidazole fragment, were synthesized by a simple and efficient nucleophilic substitution reaction between fluorene-substituted benzimidazole intermediate and 9H-carbazole [113]. Target compound D21 was produced in one step reaction 2,3-dichloroquinoxaline with 9H-carbazole [114]. Compounds D22–D24 were readily synthesized through one-step C-N coupling of a series of electron-deficient nitrogen heterocyclic rings with carbazole using classic Ullmann reaction [115]. Derivatives D25 and D26 were easily synthesized in two steps: Suzuki coupling of 4-bromophenylboronic acid with an appropriate heteroaryl halide and then Ullmann condensation of 4,4′-dibromo-2-phenylpyrimidine or 4,4′-dibromo-2- phenylpyridine with 9H-carbazole [116]. Compounds D27 and D28 were prepared by nucleophilic substitution reactions between 9H-carbazole and, respectively, 3-bromo-2-fluoropyridine or 2-bromofluorobenzene [117]. Derivative D29 was obtained in the reaction of 9-(3-(3-chlorophenoxy)phenyl)carbazole with 9H-carbazole [118].
The properties of compounds D1–D29 are presented in Table 4. TGA demonstrated that the investigated compounds possess good thermal evaporation properties and stability. Decomposition temperatures of the first 5% by weight mass loss ranged from 278 °C to 435 °C for the materials. In addition, DSC demonstrated that the host materials have high glass transition temperatures, which range from 80 °C to 150 °C. Moreover, all the hosts possess higher ET (2.61 eV–3.05 eV) to confine triplet excitons within the emitting layer. HOMO energy levels of the compounds were different and depended on chemical structures. For example, materials D3–D4, D8–D9, D11, D15, D22, and D25–D26 possessed rather high HOMO levels reaching 6.00 eV. The LUMO levels were also different and ranged from 1.09 eV to 3.51 eV.
To test host D3 in the solution-processed PhOLEDs, blue and white devices were fabricated with FIrpic guest or mixture of FIrpic: [Ir-(2-phq)3] as a guest. Impressively, even at the high brightness level of 1000 cd/m2, the blue Firpic-based PhOLED showed a low driving voltage of about 5.5 V, as well as high CE, PE, and EQE of 28.6 cd/A, 15.3 lm/W, and 15.8%, respectively. The white device demonstrated efficiencies of 29.4 cd/A, 16.4 lm/W, and 14.1% [119]. Huang et al. used the host derivative D18 for blue FIrpic dopant. At 1000 cd/m2, the device exhibited the maximal CE, PE, and EQE of 57.5 cd/A, 48.9 lm/W, and 27.0%, respectively [120].
In another series of low molar mass, two carbazol-9-yl-containing host compounds are shown in Scheme 5. The target compound E1 was synthesized via Ullmann C-N coupling reaction of 9H-carbazole with 4,4′′-bibromo-2′,3′-dipyridyl-5′,6′-diphenyl-p-terphenyl [121]. Material E2, with high triplet energy, was synthesized in two steps. First of all, 1,4-dibromobenzene was introduced to the Ge-containing skeleton(diphenylgermanium dichloride). Then, the two carbazol-9-yl moieties were connected to the core through C-N coupling reaction [122]. Host material E3 was also prepared in two steps by modulating a composition of the carbazole or pyridine moieties. At first, the copper-catalyzed Ullmann coupling reaction conditions were probed between tetrakis(4-bromophenyl)silane and 9H-carbazole, followed by palladium-catalyzed Suzuki coupling between bis(4-(carbazol-9-yl)phenyl)bis(4-bromophenyl)silane and 3-pyridylboronic acid [123]. First, brominated tetraphenylsilane intermediate was transformed into a boronic ester and then coupled with 9-(4-chloro-6-phenyl-1,3,5-triazin-2-yl)carbazole by Suzuki–Miyaura reaction to obtain host E4 [124]. Bis(4-(carbazol-9-yl)phenyl)bis(4-(4,6-diphenyl1,3,5-triazin-2-yl)phenyl)silane (E5) was synthesized by Suzuki reaction between bis(4-(carbazol-9-yl)phenyl)bis(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)silane and 2-chloro-4,6-diphenyl-1,3,5-triazine [125]. Bis(4-((4-(carbazol-9-yl)phenyl)diphenylsilyl)phenyl)(phenyl)phosphine oxide (E6) was obtained by Ullmann reaction of bis(4-((4-bromophenyl)diphenylsilyl)phenyl)(phenyl)phosphine oxide with an excess of 9H-carbazole [126].
Target compound E7 was synthesized in three steps from 4-bromophenylcarbazole by treating it with n-BuLi, then reacting it with dichlorophenylphosphine to obtain bis-4-(N-carbazolyl)phenyl)phenylphosphine, which was then oxidized with H2O2 [127]. Derivative E8 was prepared by substituting the fluorine atoms of the intermediate compound 3,3′,5,5′-tetraphenyl-4,4′-difluorodiphenyl sulfone with 9H-carbazol-9-yl unites [128]. Host products E9 and E10 were obtained by Suzuki reactions of 2-bromo-4-(carbazol-9-yl) benzonitrile or 4-bromo-2-(carbazol-9-yl)benzonitrile with 4,4,5,5-tetramethyl-2-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1,3,2-dioxaborolane [129]. Materials E11–E13 were synthesized through Suzuki coupling between 3,5-dibromobenzonitrile and a corresponding carbazol-9-yl containing phenylboronic acid [130]. Pyridine-based compounds E14 and E15 were synthesized by Suzuki–Miyaura cross-coupling of 9-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)carbazole with 3,5-dibromopyridine or 2,6-dibromopyridine [131]. 3,6-bis(2-(carbazol-9-yl)phenyl)pyridazine E16 was obtained when 9H-carbazole reacted with 3,6-bis(2-fluorophenyl)pyridazine [132].
Target compound E17 was prepared from 1-(3,5-dibromophenyl)-1,2,4-triazole and (3-(carbazol-9-yl)phenyl)boronic acid via typical Suzuki cross-coupling reaction [133]. The synthesis of compounds E18 and E19 started through classical Ullmann reaction of 1-bromo-2-chloro-4-iodobenzene and 9H-carbazole by following the treatment of the intermediate 9,9′-(2-chloro-[1,1′-biphenyl]-4,4′-diyl)bis(9H-carbazole) with 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine or with (4-(1-phenylbenzo[d]imidazol-2-yl)phenyl)boronic acid under Suzuki coupling reactions [134]. Host materials E20 and E21 were synthesized by Suzuki–Miyaura reaction of 9-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)carbazole or 9-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)carbazole with 5-bromo-2-iodopirimidine [135]. Bipolar hosts E22 and E23 were synthesized by Suzuki coupling reaction of dibromo-substituted 1,2,4-triazole with 4-(carbazol-9-yl)phenylboronic acid or 3-(9H-carbazol-9-yl)phenylboronic acid [136]. Target compounds E24 and E25 were synthesized by Suzuki coupling reaction of 9-(4-(6-bromo-[1,2,4]triazolo[1,5-a]midazol-2yl)phenyl)-9H-carbazole or 9-(4-(7-bromo-[1,2,4]triazolo[1,5-a]midazol-2yl)phenyl)-9H-carbazole with (4-(1-phenyl-1H-benzo[d]-midazole-2-yl)phenyl) boronic acid [137].
Compound E26 was prepared through Suzuki cross coupling reaction of 2-(3,5-dibromophenyl)-1-phenylbenzimidazole with 9-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)carbazole [138]. Material E27 was synthesized by nucleophilic substitution reaction between 9H-carbazole and 3,5-bis(4-fluorophenyl)-1,2,4-oxadiazole, while material E28 was obtained via Buchwald–Hartwig reaction of the 9H-carbazole and 3,5-bis(3-bromophenyl)-1,2,4-oxadiazole [139]. When 3,5-bis(3-bromophenyl)-1,2,4-oxadiazole reacted with 9H-carbazole, the objective derivative E29 was prepared using the Buchwald—Hartwig reaction [140]. Compounds E30 and E31 were obtained by one-step reaction of 9H-carbazole and difluoroarene activated by an electron withdrawing oxadiazole ring [141]. Compounds E32 and E33 were obtained by Suzuki coupling reaction of 9-[3-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]carbazole or 9-[2-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]carbazole with 2,5-bis(2-bromophenyl)-1,3,4-oxadiazole [142]. The target compound 4,6-bis(4-(carbazol-9-yl)phenyl)pyrimidine-5-carbonitrile (E34) was obtained by Suzuki_Miyaura cross-coupling reaction of 4,6-dichloropyrimidine-5-carbonitrile and 4-(carbazol-9-yl)phenylboronic acid [143].
The properties of compounds E1–E34 are presented in Table 5. DSC (for compounds E1–E16, E18–E21, E23–E32, and E34) and TGA (for compounds E1–E2, E4–E6, E8–E15, E17–E26, and E29–E34) were performed to investigate their thermal stability and film forming properties. It was found that materials E4–E5 and E25–E26 show better thermal stability (Td higher than 500 °C) in the group than other derivatives with Td values in the range 350–450 °C. DSC curves of the amorphous materials E1–E16, E18–E21, E23–E32, and E34 displayed Tg ranging from 94 °C to 252 °C. The Tg value of E5 was found at 252 °C, which was significantly higher than those of compounds E11 (94 °C) or E26 (63 °C). Phosphorescent spectra of the compounds E1–E34 were measured and values of Et were estimated to range from 2.4 eV to 3.12 eV. HOMO and LUMO of materials E1–E33 were also reported. The HOMO and LUMO energies of these compounds fall in the range of 5.2–6.4 eV and 1.38–3.0 eV, respectively.
The derivatives E1–E34 demonstrated good properties for their application in OLEDs as host materials. Yao and co-authors investigated E2 and noticed that the compound has high potential to act as the core moiety in constructing of high-performance host materials [144]. Blue light-emitting PhOLEDs using the E2 host with Firpic demonstrated a maximum luminance of 10000 cd/m2 and a maximum CE of 15.2 cd/A. An EQE of 24% and a PE of 46 lm/W were achieved at the practical brightness of 100 cd/m2 by using E14 as the host for the FIrpic dopant-based blue device as described D. Kim et al. [145]. Host E28, having blue PhOLEDs with FIrpic quest, was fabricated by Q. Li and co-workers. The performances of 12.0 cd/A, 9.8 lm/W, and 5.8% for CE/PE/EQE were achieved in the most effective device [146]. Compared to other carbazole-based host compounds in the group, the highest EQE of 25.6% was achieved in green PhOLED using host E25.
Another group of low molar mass twin carbazole-based compounds containing phenantherene, quinoline, benzimidazo[2,1-b]benzothiazole, 9H-pyrido[2,3-b]indole, carboline, dibenzothiophene, benzofuran, or fluorine central core is shown in Scheme 6. Buchwald–Hartwig coupling reaction of 9H-carbazole with 3,6-dibromophenanthrene, 2,9-dibromobenzo[f]quinoline, or 3,9-dibromobenzo[f]quinoline produced the hosts F1–F3 [146]. Two compounds F4 and F5 were prepared by copper-catalyzed Ullmann coupling of di-halogenated benzimidazo[2,1-b]benzothiazole with an excess of 9H-carbazole [147]. Compound F6 was obtained via the Ullmann coupling reaction of 9-(3,5-dichlorophenyl)–2,7-diazacarbazole and 9H-carbazole [148]. Materials F7–F11 were also obtained by Ullmann coupling reactions of 9-(6-bromopyridin-3-yl)-6-(carbazol-9-yl)-9H-pyrido[2,3b]indole, 9-(6-bromopyridin-2-yl)-6-(carbazol-9-yl)-9H-pyrido[2,3b]indole, 9-(4-bromophenyl)-6-(carbazol-9-yl)-9H-pyrido[2,3-b]indole, 9-(3-bromophenyl)-6-(carbazol-9-yl)-9H-pyrido[2,3-b]indole, or 5-(6-bromophenyl)pyridine-2-yl)-8-(carbazol-9-yl)-5H-pyrido[3,2-b]indole with 9H-carbazole, respectively [149,150,151]. Host F12 was easily synthesized by an Ullmann coupling reaction of 2,8-dibromo[b,d]dibenzothiophene with 9H-carbazole [152]. Material F13 was prepared by a Suzuki coupling reaction of 2,8-dibromo[b,d]dibenzothiophene and 9-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)carbazole [153]. Derivatives F14 and F15 were obtained by an Ullmann coupling reactions of 9,9-bis(3-bromophenyl)-9H-thioxanthene or 9,9-bis(3-bromophenyl)-9H-thioxanthene-10,10-dioxide with 9H-carbazole, respectively [154]. Reactions of 4,8-dibromodibenzo[b,d]furan or 2,8-dibromodibenzo[b,d]furan with 9H-carbazole through Buchwald–Hartwig cross-coupling yielded F16 and F17 [155]. 2,2′-Di(carbazol-9-yl)-4,4-bidibenzo[b,d]furan (F18) was synthesized by Suzuki coupling reaction between boronic acid of 2-(9-carbazolyl)dibenzofuran and iodinated 2-(9-carbazolyl)dibenzofuran [156]. Compound F19 was obtained by the coupling of dibromo-spiro[fluorene-9,9′-xanthene] derivative with 9H-carbazole through Ullmann coupling reaction [157]. Buchwald—Hartwig amination of 9,9-bis(4-bromophenyl)fluorene with 9H-carbazole yielded material F20 [158].
The characteristics of compounds F1–F20 are presented in Table 6. These compounds exhibit rigid flat structures and are thus regarded as materials with outstanding thermal stability. The highest thermal stability was achieved by compounds F9 and F10 with a thermal stability higher than 500 °C. Meanwhile, the highest Tg was obtained for compounds F18 and F19, i.e., 181 °C and 170 °C, respectively. The Et value of these compounds ranged from 2.56 eV to 3.04 eV, while HOMO and LUMO energies of the host molecules F1–E20 were in the ranges 6.07–5.24 eV and 2.98–1.82 eV, respectively. The compounds F4, F5, F14, and F15 achieved the highest Et values exceeding 3 eV, indicating that these compounds are suitable as host materials for OLED devices of all colours.
To verify the design concept of the synthesized host materials F1–F20, the investigators prepared green or blue PhOLEDs. The blue devices with FIrpic dopant dispersed in F8 was described by Yu and co-workers [159]. They demonstrated PhOLED with EQE of 23.7%, CE of 44.8 cdA−1, and PE of 31.3 lmW−1. Blue devices using F13 with Firpic emitter were also formed by W.C. Lin et al., and a maximum EQE of 13.9% (29.7 cd/A and 18.6lm/W) was obtained [160]. A maximal EQE of 29.0% was achieved for an optimized blue device based on F15 host and Firpic dopant. Green devices using F19 with Ir(ppy)3 dopant were also fabricated. PhOLED doped with 10wt% of the emitter achieved CE of 21.0 cd/A, PE of 11.9 lm/W, and maximum luminance of 49,000 cd/m2.
A group of low molar mass carbazole-based twin compounds containing substituents in the carbazole ring is shown in Scheme 7. The target compounds G1 and G2 were prepared by Ullmann coupling reactions of 2,8-dibromodibenzofuran with 2,7-dimethoxycarbazole or 3,6-dimethoxycarbazole, respectively [161]. Materials G3 and G4 were synthesized by refluxing 1,3-diiodobenzene with 3,6-dimethoxycarbazole or 3,6-di(tert-butyl)carbazole [162]. Three derivatives G5–G7 were conveniently synthesized by a one-step aromatic nucleophilic substitution reaction when 2,6-difluoropyridine reacted with 2,7-dimethyl-9H-carbazole, 3,6-dimethyl-9H-carbazole, or 3,6-di-tert-butyl-9H-carbazole [163].
1-Bromo-3,5-difluorobenzene was modified with two t-butyl substituted carbazolyl units by a reductive amination reaction and with an additional t-butyl substituted diphenylamine unit with the Buchwald reaction to obtain compound G8 [164]. Host material G9 was realized with an Ullmann coupling reaction between 2,6-bis(2-bromophenyl)pyridine and 3,6-di(tert-butyl)carbazole [165]. Reactions of 2-[3,6-di(tert-butyl)carbazol-9-yl]benzoic acid chloride with 1,2- or 1,3-ditetrazolebenzenes easily yielded materials G10 and G11 [166]. Carbazole/fluorene-based material G12 was synthesized by the aromatic C-N coupling of 2,7-dibromo-9,9-diphenylfluorene with 3,3″,6,6″-tetra-tert-butyl-9′H-9,3′:6′,9″-tercarbazole [167]. Compound G13 was prepared in one step N-Si nucleophilic substitution coupling of the chlorophenylsilane with lithiated carbazole intermediate [168]. Compound G14 was synthesized through a Suzuki cross-coupling reaction between 1,4-diiododurene and the carbazole-containing boronic acid [169]. A Suzuki–Miyaura coupling reaction between the [4-(3,6-dibutylcarbazol-9-yl)phenyl]boronic acid and bis(4-bromophenyl)(diphenyl)silane allowed us to obtain the target compound G15 [170].
The properties of compounds G1–G15 and devices using the hosts are presented in Table 7. Derivatives G1–G7 and G9–G14 demonstrated relatively high thermal stability. The temperatures of the onsets of weight loss were in the range of 300–495 °C. In the second DSC heating scans, the materials G1–G7, G9–G12, and G15 demonstrated glass transitions with Tg ranging from 79 to 304 °C. For example, the Tg value of G12 was found to be higher by 200 °C in comparison to that of G3. The host materials G1–G15 were characterized by high triplet energies ranging from 2.61 to 3.08 eV. The HOMO/LUMO energy levels of derivatives G1–G15 were different and ranged, respectively, from 5.8 eV to 5.1 eV and from 2.97 eV to 1.4 eV.
In order to estimate the hosting properties of G1–G15, PhOLEDs were fabricated and investigated. A green device using G4 with a Firpic emitter showed EQE up to 22.0%. A device using FCNIr doped in G8 provided a high EQE of 16.4% in the deep blue region with a colour coordinate of (0.14, 0.19). Pei et al. fabricated sky-blue OLED with 2CzPN dopant. The device hosted by G9 realized the CE of 28.9 cd/A, PE of 23.3 lm/W, and EQE of 11.7%. To evaluate the EL properties of the synthesized compound G15 as solution-processable host materials, the authors fabricated green PhOLEDs with Ir(ppy)3 dopant, and the highest luminous and power efficiency values of 7.6 cd/A and 3 lm/W were obtained.
Groups of low molar mass twin compounds with two carbazolyl fragments connected through third position to the central unit is shown in Scheme 8. Material H1 was synthesized by using lithiation of 3-bromo-9-phenylcarbazole with n-BuLi and then the compound was quenched with diethoxydiphenylsilane. For the synthesis of H2, at first the intermediate as bis(9-phenylcarbazol-3-yl)sulphane was prepared by the Pd-catalyzed coupling reaction of 3-bromo-9-phenylcarbazole with potassium thioacetate, which was then oxidized with meta-chloroperoxybenzoic acid to obtain H2 [171]. The host material H3 was efficiently synthesized from 9H-thioxanthen-9-one and 9-phenylcarbazole in the presence of Eaton’s reagent for the Friedel–Crafts-type substitution [172]. Compound H4 was obtained in two steps. In the first step, a mixture of 2-phenylindole-3-carbaldehyde and 9H-carbazole was treated with HCl to yield di(9H-carbazol-3-yl)(2-phenyl-1H-indol-3-yl)methane, which reacted with epichlorohydrin in the presence of potassium tert-butoxide to give the objective derivative H4 [173]. Hosts H5 and H6 were synthesized by a Suzuki reaction of (9-phenylcarbazol-3-yl)boronic acid with 2,5-dibromopyrimidine or 4,6-dibromopyrimidine [173]. Suzuki–Miyaura cross-coupling reaction of 3,4-dibromo-2,5-dimethylthiophene with 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)carbazole produced host H7 [174]. Compound H8 was synthesized via Suzuki coupling between 3,6-dibromo-4,5-dimethylpyridazine and (9-phenylcarbazol-3-yl)boronic acid [175]. The 1H,1′H-2,2′-diimidazole was treated with 3-bromo-9-phenylcarbazole under Ullmann reaction conditions to give host material H9 [176]. Compounds H10 and H11 were obtained by the Suzuki coupling reaction of the 2-(3,5-dibromophenyl)benzo[d]oxazole or 2-(3,5-dibromophenyl)benzo[d]thiazole intermediates and (9-phenyl-9H-carbazol-3-yl)boronic acid and dibenzo[b,d]furan-4-ylboronic acid [177]. 1,2,4-Triazole-based host material H12 was synthesized from 2-[1,3-bis(4-bromophenyl)-1,2,4-triazol-5-yl]pyridine and (9-phenylcarbazol-3-yl)boronic acid by Suzuki coupling reaction [178].
Characteristics of the compounds H1–H12 are presented in Table 8. Thermal stabilities of these hosts were investigated by TGA and DSC. The materials H1–H8 and H10–H12 possess high Td values of 366 °C, 331 °C, 464 °C, 242 °C, 420 °C, 403 °C, 420 °C, 390 °C, 425 °C, 371 °C, 442 °C, and 432 °C, respectively. The Tg of compouds H1–H3, H5–H8, and H10–H12 ranged from 85 °C to 145 °C. The highest Tg of 145 °C demonstrated compound H11. The Et of the compounds H5–H6 and H8–H12 ranged from 2.64 eV to 2.8 eV, while reaching 3 eV for compounds H1–H4 and H7. HOMO energy levels of compounds H1–H12 were between 4.93 and 5.90 eV and depended on the structure of acceptor the fragment of the molecule, while the LUMO of the derivatives H1–H12 were from 0.66 eV to 2.53 eV.
A device based on the host H1 and co-host PO-T2T with 10 wt% of green emitter 4CzIPN achieved high EQE of 21.1%, CE of 56.4 cd/A, and PE of 59.1 lm/W. Green devices using DACT-II dopant in H6 with optimized doping concentrations of 20 wt % of the emitter reacted also high EQE of 22.7% with PE of 53.4 lm/W. Blue PhOLED with H7 host and FIrpic dopant achieved an EQE of 18.9%. Green and red devices using Ir(ppy)3 or Ir(pq)2acac emitter for H8 host were also reported. The green device exhibited EQE of 22.2%, and red device yielded also excellent efficiency with the EQE of 20.0%. A blue device with an emitting layer H9: FIrpic demonstrated efficiencies of 21.0 cd/A and of12.0 lm/W. Green PhOLED structures using host materials H10 or H11 with Ir(ppy)2(acac) dopant were presented. The maximum efficiencies for the H10- and H11-based devices were a CE of 44.7 cd/A and 50.7 cd/A, and PE of 42.8 lm/W and 50.1 lm/W, respectively. A red emitting diode with H12 was fabricated by utilizing Ir(piq)2acac as the emitter, and an EQE of 14.1% with a CE of 9.7 cd/A were reached.

4. Host Materials with 3(2)-Aryl(arylamino)-Substituted Carbazole Fragments

The structure of some 3(2)-aryl(arylamino)-substituted carbazoles as host materials for PhOLEDs are shown in Scheme 9. Compounds I1–I4 were synthesized by an optimized Ullmann cross-coupling reaction between 9-ethyl and 3-iodocarbazole and 9H-carbazole, diphenylamine, phenoxazine, or phenothiazine, respectively. Material I5 was obtained by an oxidation of I4 in presence of hydrogen peroxide [179]. The starting materials for compound I6–I7 were obtained when 9-ethylcarbazole-3-carbaldehyde or 9-phenylcarbazole-3-carbaldehyde reacted with 2-hydrazinopyridine. The target compounds I6–I7 were then obtained in the reaction of 9-ethyl-3-((2-(pyridin-2-yl)hydrazono)methyl)carbazole or 9-phenyl-3-((2-(pyridin-2-yl)hydrazono)methyl)carbazole with [bis(trifluoroacetoxy)iodo] benzene [180].
The bipolar host material, I8, was synthesized by reacting 3-bromo-9-phenylcarbazole with n-butyllithium to obtain the lithiate intermediate, which was subsequently quenched with fluorodimesityl borane [181]. Compound I9 was obtained through a Suzuki cross-coupling reaction of 3,5-dipyrazolyl-1-bromobenzene with (9-phenylcarbazol-3-yl)boronic acid [182]. Derivative I10 was obtained when 3-(1-(4-bromophenyl)benzo[d]imidazol-2-yl)-9-phenylcarbazole reacted with n-BuLi. Meanwhile, when 3-(1H-enzo[d]imidazol-2-yl)-9-phenylcarbazole reacted with 9-(4-bromophenyl)carbazole or 9-(3-bromopropyl)carbazole, compounds I11 and I12 were obtained [183]. 4-(9-Phenylcarbazol-3-yl)pyrolo[1,2-a]quinoxaline (I13) was synthesized by reacting 9-phenylcarbazole-3-carbaldehyde with 2-(pyrol-1-yl)benzenamine [184]. Compounds I14–I15 were easily obtained by the palladium-catalyzed Suzuki coupling reaction of (9-phenylcarbazol-2-yl)boronic acid or (9-phenylcarbazol-3-yl)boronic acid with (4-bromophenyl)diphenylphosphine oxide [185]. Bipolar host I16 was synthesized by the Suzuki coupling reaction of 2-(3-bromophenyl)-1-phenylbenzo[d]imidazole and 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)carbazole [186].
The Suzuki coupling reaction of carbazolyl-containing boronic acids with 4-(5-(4-bromophenyl)-3-(pyridin-2-yl)-3H-1,2 4,4-triazol-2-yl)benzonitrile produced materials I17 and I18 [187]. The synthesis of I19 was very simple and achieved in one step: [4-(carbazol-9-yl)phenyl]boronic acid was allowed to react with 2-(3-bromophenyl)-4,6-diphenyl-1,3,5-triazine through the Suzuki coupling reaction [188]. Products I20 and I21 were obtained by the Suzuki coupling of 3-bromo-9-phenylcarbazole or 3-bromo-9-(2-naphthyl)carbazole with 4-(1-phenyl-1H-benz[d]imidazol-2-yl)phenylboronic acid [189]. Compounds I22–I25 were also prepared by the Suzuki coupling reaction of the (9-phenylcarbazol-3-yl)boronic acid with 9-(2-bromophenyl)carbazole-3-carbonitrile, 9-(3-bromophenyl)carbazole-3-carbonitrile, 3-bromo-2-(dibenzo[b,d]furan-4-yl)pyridine, or 3-bromo-2-(dibenzo[b,d]thiophen-4-yl)pyridine, respectively [190,191]. In reactions of 9-phenyl-9′H-(1,2′-bicarbazole) or 9-phenyl-9′H-(1,3′-bicarbazole) with 2-chloro-4,6-diphenyl-1,3,5-triazine materials I26–I27 were received [192]. The target compounds I28–I30 were obtained by Ullmann coupling between N-(4-(9H-carbazol-3-yl)phenyl)-N-phenylbenzenamine and different halogenated bipyridine derivatives [193]. Suzuki coupling reaction of 2-chloro-4,6-diphenyl-1,3,5-triazine or 2-chloro-4,6-diphenylpyrimidine with (9-[4-(diphenylamino)phenyl]carbazol-2-yl)boronic acid produced target compounds I31 and I32 [194].
Compounds I6, I8–I9, I11, I14–I19, I24–I25, I28, and I30 have high Tg values of 112, 105, 89, 156, 101, 97, 103, 115, 116, 95, 245, 196, 110, and 108 °C, respectively. Td values of the compounds I1–I19, I24–I25 and I28–I32, corresponding to 5% weight loss, ranged from 180 to 444 °C. All these materials exhibit high triplet energies of 2.34−3.02 eV, which are high enough to guarantee their capability to act as hosts for phosphorescent emitters. The HOMO levels of these compounds ranged from 5.37 to 6.1 eV. The LUMO levels of these derivatives ranged from 1.84 to 3.26 eV. All the mentioned characteristics are summarized in Table 9.
To evaluate the utility of these compounds as host materials, the researchers fabricated various PhOLED devices. Blue and green light-emitting phosphorescent devices with structures of ITO/PEDOT:PSS/TAPC/I9: Firpic or Ir(ppy)3/TmPyPB/LiF/Al were fabricated. The I9-hosted OLEDs achieved high efficiencies of 15.8% and 13.3%, respectively, for the blue and green devices. Green PhOLED hosted by I14 also showed excellent performances with a maximum CE of 65.2 cd/A, a PE of 74.3 lm/W, and an EQE of 18.7%. To evaluate compounds I28–I30 as host materials for phosphorescent emitters, Chatterjee et al. selected three phosphorescent dopants: green (ppy)2Ir(acac), yellow (bt)2Ir(acac), and red (mpq)2Ir(acac) in structures, which are described in Table 9. I30-based green PhOLED achieved maximum CE of 79.8 cd/A and EQE of 22.0%, and I29-based yellow device demonstrated CE of 57.3 cd/A and EQE reaching 22.4%.

5. Host Materials with 3,6(2,7)-Diaryl(arylamino)-Substituted Carbazole Fragments

3,6(2,7)-Diaryl(arylamino)-substituted carbazoles as host materials for PhOLEDs are shown in Scheme 10. 3,6-disubstituted carbazole compound J1 and J3 were synthesized by Ullmann coupling reaction of 3,6-diiodo-9-ethylcarbazole with N,N-di(4′-methylphenyl)amine or 3,6-di(tert-butyl)-9H-carbazole, respectively. The 2,7-disubstituted carbazole-based derivative J2 was synthesized by palladium-catalyzed aromatic C-N coupling reaction of 2,7-dibromo-9-ethylcarbazole with N,N-di(4′-methylphenyl)amine [195,196]. Carbazole–fluorene hybrid materials J4–J6 have been synthesized via mild room-temperature one-step Friedel–Crafts reactions of 9-octylcarbazole with various 9-phenyl-9-fluorenols [197]. Suzuki coupling of 2-(4-bromophenyl)-1-phenylbenzimidazole or ortho(meta)-bromo-1-phenylbenzo[d]imidazoles with 9-phenylcarbazole-based di-boronic ester gave compounds J7–J9 [198,199,200].
9-Phenyl-3,6-ditritylcarbazole J10, 9-phenyl-3,6-bis(triphenylsilyl)carbazole J11 and 3,6-bis(diphenylphosphoryl)-9-phenylcarbazole J12 were prepared and investigated by Nagai et al. [201].
C-N coupling reactions of 3,6-diiodo-9-phenylcarbazoles with various indoles were used to synthesize compounds J13–J15 [202]. Target compounds J16–J21 were prepared by CuI-mediated Ullmann reactions from various 3,6-dibrominated 9-arylcarbazoles and 9H-carbazole or diphenylamine, respectively [203,204]. A Suzuki coupling reaction of 3,6-dibromo-9-(4-bromophenyl)carbazole with 4-biphenylboronic acid yielded the compound J22 [205]. 9′-Triphenylsilanyl[9,3′,6′,9″]tercarbazole (J23) was synthesized from the N-unsubstituted carbazole derivative, which was first treated with n-BuLi to give a lithiated intermediate followed by its quenching with chlorotriphenylsilane [206]. Compound J24 was obtained by an Ullmann reaction of 3,6-dibromo-9-[4-(triphenylsilyl)phenyl]carbazole with excess of 9H-carbazole [207]. Objective product J25 was obtained in reaction 3,6-dibromo-9-(4-bromophenyl)carbazole with t-BuLi, followed by an addition of dimesitylboron fuoride (Mes2BF) [208]. The target compounds J26 and J27 were obtained through a two-step procedure including phophorization and oxidation of 2-(3,6-bis[3-(carbazol-9-yl)phenyl]carbazol-9-yl)ethanol or 6-(3,6-bis[3-(carbazol-9-yl)phenyl]carbazol-9-yl)hexan-1-ol, respectively [209].
The described host materials exhibit good thermal stability with Td ranging from 234 to 498 °C. It was found that compound J25 shows the lowest Td of 234 °C and compound J19 shows the highest Td of 498 °C. It could be seen from the DSC measurements that materials J2–J8, J10, J13–J20, and J23–J27 exhibited high or very high values of Tg ranging from 89 to 210 °C. Among them, J6 shows the highest Tg of 244 °C.
These compounds also possess high triplet energy levels (Et in the range 2.51–3.01 eV) due to limited conjugation between electron–donor and electron–acceptor moieties. HOMO and LUMO energy levels of the materials J2–J27 were described. The HOMO values of J26 and J27 were about 6.4 eV, which are higher than those of other compounds with HOMO levels ranging from 4.81 eV to 5.66. Due to differences in electron affinity of the molecules, the lowest LUMO energy level of 1.27 eV was achieved for J11. In contrast, J26 possesses the highest LUMO of 2.83 eV. All the briefly described characteristics and efficiencies of OLEDs using some of the mentioned materials are presented in Table 10.
Devices with hosts J1 or J2 and the TCz1 emitter were fabricated by the step-by-step vacuum deposition process. Highly efficient violet and blue light-emitting OLEDs exhibited, respectively, CE of 5.3 and 13.5 cd/A, high brightness of 3458 and 12535 cd/m2 as well as EQE of 5 and 17% [210]. Blue-emitting PhOLEDs were also fabricated with the structure of the emitting layer host J3: FIrpic. The device had an efficiency of 31 cd/A at 124 cd/m2 [211]. Chou et al. fabricated PhOLEDs using J8 or J9 hosts with green (PBi)2Ir(acac), red Os(bpftz)2(PPhMe2)2, blue FIrpic, or yellow (Bt)2Ir(acac) dopants. The devices with J9 as a universal host achieved EQEs of 16.7% for red, 16.7% for green, 8.8% for blue, and 17.5% for yellow emission under the same device configuration. Blue and green devices using host materials J16–J19 with FIrpic or Ir(ppy)3 dopant were formed by Wang and co-workers. J19-based PhOLEDs showed the best charge-balancing state and generated an EQE of 27.0% (CE of 51.9 cd/A and a PE of 46.5 lm/W), which remained at 23.6% even at the practical brightness of 1000 cd/m2.

6. Conclusions

In summary, several groups of low molar mass carbazole-based host materials, i.e., 9-arylcarbazoles, twin derivatives containing two carbazolyl fragments, 3(2)-aryl(arylamino)-substituted, and 3,6(2,7)-diaryl(diarylamino)-substituted carbazoles are described in this review article. These compounds were prepared by using various reactions such as Ullmann coupling, Suzuki–Miyaura coupling, Buchwald–Hartwig coupling, nucleophilic substitution process, and others. Thermal, electrochemical, and optoelectronic properties of the hosts as well as their utilization in phosphorescent organic light-emitting diodes are summarized. The thermal stability of the compounds was confirmed by thermogravimetric analysis, and decomposition temperatures ranging from 145 °C to 575 °C were demonstrated indicating the good thermal stability of some materials. Differential scanning calorimetry revealed glass transition temperatures of the derivatives ranging from 49 °C to 260 °C. Electrochemical measurements for the compounds by cyclic voltammetry were used to determine their oxidation and reduction potentials, from which the HOMO and LUMO energy levels were calculated. The HOMO levels range from 5.1 to 6.5 eV, while the LUMO levels ranged from 1.02 eV to 4.97 eV and depend on the chemical structures of the compounds. Phosphorescent emission spectra indicated different triplet energies of the materials attributed to their distinct substituents and ranged from 2.25 eV to 3.62 eV. PhOLED devices incorporating these compounds as host materials exhibited diverse electroluminescent performances, current efficiency, power efficiency, and external quantum efficiency. Notably, compound D27 demonstrated high thermal stability and favourable electrochemical properties, making it a promising host material for sky-blue phosphorescent OLEDs using FIrpic dopant. The best device showed remarkable performance with a CEmax of 66.4 cd/A, PEmax of 57.9 lm/W, and an EQEmax of 32%, outperforming many other materials. Compounds B15 and F15 were also noteworthy, achieving high efficiencies reaching 30% in the sky-blue devices with the FIrpic dopant. Meanwhile, green light-emitting PhOLED with host A27 exhibited high EQE of 28.0%, CE of 97.7 cd/A and PE of 102.5 lm/W all superior to other analogues and many reported host materials. Red light PhOLEDs employing a conventional dopant material (piq)2Ir(acac) and host compound J22 in the emissive layer showed nearly 100% IQE, corresponding to the EQE of 19.3%, CE of 16.4 cd/A, and PE of 13 lm. Overall, these findings demonstrate the potential of carbazole-based derivatives as effective host materials for OLED applications. The results are also of significant interest for the development of new efficient hosts and high-performance devices using the future host compounds.

Author Contributions

Writing—review and editing, G.K.; writing—review and editing, S.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was conducted in the frame of the project with support from the Research Council of Lithuania (Grant No. S-LLT-25-2).

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

2-TNATA4,4′,4′′-tris[2-naphthyl(phenyl)amino] triphenylamine
4CzIPN1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene
Alq3tris(8-hydroxyquinolinato)aluminum
AcDbp2,7-bis(9,9-dimethylacridin-1′(9H)-yl)dibenzo [a,c]phenazine
B3PYMPM4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine, 4,6-Bis(3,5-di-3-pyridinylphenyl)-2-methylpyrimidine
BCP4,7-diphenyl-1,10-phenanthroline
BCFAN-([1,10-biphenyl]-4-yl)-9,9- dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine
BCFNN-([1,1′-biphenyl]-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine
Bebq2bis(10-hydroxybenzo[h]quinolinato)beryllium
Bphen4,7-diphenyl-1,10-phenanthroline
BPBPAN,N,N′,N′-Tetra(4-biphenylyl)-4,4′-biphenyldiamine
(Bt)2Ir(acac)bis(2-phenylbenzothiazolato)(acetylacetonate)iridium(III)
CEcurrent efficiencies
CuPccopper phthalocyanine
CzSi9-(4-tert-Butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole
DACT-II9-[4-(4,6-diphenyl-1,3,5- triazin-2-yl)phenyl]-N,N,N′,N′-tetraphenyl-9H-carbazole-3,6-diamine
DBFTrz2,8-bis(4,6-diphenyl-1,3,5-triazin-2-yl)dibenzo-[b,d]furan
DNTPD4,4′-bis[N-[4-{N,N-bis(3-methylphenyl)amino}phenyl]-N-phenylamino]biphenyl
DSCdifferential scanning calorimetry
DPPSdiphenyl-bis [4-(pyridin-3-yl)phenyl]silane
DPEPObis [2-(diphenylphosphino)phenyl]ether oxide
DTAF9,9-di [4-(di-p-tolyl)aminophenyl]fluorine
Ettriplet energies
EQEexternal quantum efficiencies
FCNIrpicbis(3,5-difluoro-4-cyano-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium(III)
FIr6bis(2,4-difluorophenylpyridinato)-tetrakis(1-pyrazolyl)borate iridium(III)
FIrpicbis [2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium
HAT-CN1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile
HOMOthe highest occupied molecular orbital
LUMOthe lowest unoccupied molecular orbital
TCTAtris(4-carbazoyl-9-ylphenyl)amine
TAPC1,1-bis[(di-4-tolylamino)phenyl]cyclohexane
TAZ3-(4-biphenyl)-4-phenyl-5-tert -butylphenyl-1,2,4-triazole
TmPyPB1,3,5-tri(m-pyridin-3-ylphenyl)benzene
Tgglass transition temperatures
TCz13,6-bis(carbazol-9-yl)-9-(2-ethyl-hexyl)-9H -carbazole
Tris-PCz9-phenyl-3,6-bis(9-phenyl-9Hcarbazol-3-yl)-9H-carbazole
Ir(MDQ2(acac)bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate) iridium(III)
Ir(mppy)3tris [2-(p-tolyl)pyridine]iridium(III)
Ir(ppy)3tris(2-phenylpyrydine(iridium(III)
Ir(dbfmi)mer-tris(N-dibenzofuranyl-N′-methylimidazole)iridium(III)
Ir(pq)2(acac)bis(1-phenylisoquinoline)(acetylacetonate)iridium(III)
Ir (ppz)3tris(1-phenylpyrazolato)iridium
ITOindium tin oxide
IQEinternal quantum efficiency
mCPN,N′-dicarbazolyl-3,5-benzene
(mpq)2Ir(acac)(2-(3-methylquinolin-2-yl)phenyl) iridium(III) acetylacetonate
m-MTDATA4,4′,4′′-tris[(3-methylphenyl)phenylamino]triphenylamine
MoO3Molybdenum trioxide
NPBN,N0-bis-[(1-naphthalenyl)-N,N0-bis-phenyl]-(1,10-biphenyl)-4,40-diamine
OLEDorganic light-emitting diode
Os(bpftz)2
(PPhMe2)2		bis(3-(trifluoroMethyl)-5-(4-tert-butylpyridyl)-1,2,4-triazolate) dimethylphenylphosphine
OXD-71,3-bis [2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene
PCzAc9,10-dihydro-9,9-dimethyl-10- (9-phenyl-9H-carbazol-3-yl)-acridine
PEpower efficiencies
PEDOT: PSSpoly(3,4-ethylene-dioxythiophene): poly(styrene-sulfonate)
PHOLEDphosphorescent organic light-emitting diode
PO-01bis(4-phenylthieno [3,2-c]pyridinato-N,C2′) (acetylacetonate) iridium(III)
poly-TPDpoly(N,N′-bis-4-butylphenyl-N,N′-bisphenyl)benzidine
PO-T2TLiq2,4,6-tris [3-(diphenylphosphinyl)phenyl]-1,3,5-triazine
(PBi)2Ir(acac)bis(1,2-dipheny1-1H-benzoimidazole) iridium(III) (acetylacetonate)
PtN3N-ptbtetradentate cyclometalated Pt(II) complex
TAPC1,1-bis[(di-4-tolylamino)phenyl]cyclohexane
TCTAtris(carbazol-9-yl)-triphenylamine
TmPyPb1,3,5-tris(3-pyridyl-3-phenyl)benzene
TPBi2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)
(tphpy)2Ir(acac)bis [2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III)
TTAtriplet-triplet annihilation
TGAthermos-gravimetric analysis
Tdthermal decomposition temperatures
TSPO1Diphenyl [4-(triphenylsilyl)phenyl]phosphine oxide
ZADN2-[4-(9,10-di-naphthalen-2-yl-anthracen-2-yl)-phenyl]-1-phenyl-1H-benzoimidazole

References

  1. Tang, C.W.; VanSlyke, S.A. Organic electroluminescent diodes. Appl. Phys. Lett. 1987, 51, 913. [Google Scholar] [CrossRef]
  2. Tyan, Y.S.J. Organic light-emitting-diode lighting overview. Photonics Energy 2011, 1, 011009. [Google Scholar] [CrossRef]
  3. Chen, H.W.; Lee, J.H.; Lin, B.Y.; Chen, S.; Wu, S.T. Liquid crystal display and organic light-emitting diode display: Present status and future perspectives. Sci. Appl. 2018, 7, 17168. [Google Scholar] [CrossRef]
  4. Xu, R.P.; Li, Y.Q.; Tang, J.X. Recent advances in flexible organic light-emitting diodes. J. Mater. Chem. C 2016, 4, 9116. [Google Scholar] [CrossRef]
  5. Jou, J.H.; Kumar, S.; Agrawal, A.; Li, T.H.; Sahoo, S. Approaches for fabricating high efficiency organic light emitting diodes. J. Mater. Chem. C 2015, 3, 2974. [Google Scholar] [CrossRef]
  6. Yokoyama, D.J. Molecular orientation in small-molecule organic light-emitting diodes. Mater. Chem. 2011, 21, 19187. [Google Scholar] [CrossRef]
  7. Geffroy, B.; Roy, P.L.; Prat, C. Organic light-emitting diode (OLED) technology: Materials, devices and display technologies. Polym. Int. 2006, 55, 572. [Google Scholar] [CrossRef]
  8. Duan, L.; Hou, L.; Lee, T.W.; Qiao, J.; Zhang, D.; Dong, G.; Wang, L.; Qiu, Y. Solution processable small molecules for organic light-emitting diodes. J. Mater. Chem. 2010, 20, 6392. [Google Scholar] [CrossRef]
  9. Baldo, M.A.; O’Brien, D.F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson, M.E.; Forrest, S.R. Highly efficient phosphorescent emission from organic electroluminescent devices. Nature 1998, 395, 151. [Google Scholar]
  10. Poriel, C.; Rault-Berthelot, J. Pure Hydrocarbons: An Efficient Molecular Design Strategy for the Next Generation of Host Materials for Phosphorescent Organic Light-Emitting Diodes. Acc. Mater. Res. 2022, 3, 379. [Google Scholar] [CrossRef]
  11. Gong, X.; Ostrowski, J.C.; Moses, D.; Bazan, G.C.; Heeger, A.J. Red electrophosphorescence from polymer doped with iridium complex. Appl. Phys. Lett. 2002, 81, 3711. [Google Scholar] [CrossRef]
  12. Tsuzuki, T.; Shirasawa, N.; Suzuki, T.; Tokito, S. Color Tunable Organic Light-Emitting Diodes Using Pentafluorophenyl-Substituted Iridium Complexes. Adv. Mater. 2003, 15, 1455. [Google Scholar] [CrossRef]
  13. Jeon, W.S.; Park, T.J.; Kim, S.Y.; Pode, R.; Jang, J.; Kwona, J.H. Ideal host and guest system in phosphorescent OLEDs. Org. Electron. 2009, 10, 240. [Google Scholar] [CrossRef]
  14. Strohriegl, P.; Wagner, D.; Schrögel, P.; Hoffmann, S.T.; Köhler, A.; Heinemeyer, U.; Münster, I. Novel host materials for blue phosphorescent OLEDs. Proc. SPIE 2013, 8829, 882906. [Google Scholar]
  15. Yeh, S.J.; Wu, M.F.; Chen, C.T.; Song, Y.H.; Chi, Y.; Ho, M.H.; Hsu, S.F.; Chen, C.-H. New Dopant and Host Materials for Blue-Light-Emitting Phosphorescent Organic Electroluminescent Devices. Adv. Mater. 2005, 17, 285. [Google Scholar] [CrossRef]
  16. Yook, K.S.; Lee, J.Y. Bipolar Host Materials for Organic Light-Emitting Diodes. Chem. Rec. 2016, 16, 159. [Google Scholar] [CrossRef]
  17. Adachi, C.; Kwong, R.C.; Djurovich, P.; Adamovich, V.; Baldo, M.A.; Thompson, M.E.; Forrest, S.R. Endothermic energy transfer: A mechanism for generating very efficient high-energy phosphorescent emission in organic materials. Appl. Phys. Lett. 2001, 79, 2082. [Google Scholar] [CrossRef]
  18. Holmes, R.J.; Forrest, S.R.; Tung, Y.J.; Kwong, R.C.; Brown, J.J.; Garon, S.; Thompson, M.E. Blue organic electrophosphorescence using exothermic host–guest energy transfer. Appl. Phys. Lett. 2003, 82, 2422. [Google Scholar] [CrossRef]
  19. Xiao, L.; Su, S.J.; Agata, Y.; Lan, H.; Kido, J. Nearly 100% Internal Quantum Efficiency in an Organic Blue-Light Electrophosphorescent Device Using a Weak Electron Transporting Material with a Wide Energy Gap. Adv. Mater. 2009, 21, 1271. [Google Scholar] [CrossRef]
  20. Adachi, C.; Baldo, M.A.; Thompson, M.E.; Forrest, S.R. Nearly 100% internal phosphorescence efficiency in an organic light emitting device. J. Appl. Phys. 2001, 10, 5048. [Google Scholar] [CrossRef]
  21. O’Brien, D.F.; Baldo, M.A.; Thompson, M.E.; Forrest, M.E.S.R. Improved energy transfer in electrophosphorescent devices. Appl. Phys. Lett. 1999, 74, 442. [Google Scholar] [CrossRef]
  22. Tao, Y.; Yang, C.; Qin, J. Organic host materials for phosphorescent organic light-emitting diodes. Chem. Soc. Rev. 2011, 40, 2943. [Google Scholar] [CrossRef]
  23. Chaskar, A.; Chen, H.F.; Wong, K.-T. Bipolar Host Materials: A Chemical Approach for Highly Efficient Electrophosphorescent Devices. Adv. Mater. 2011, 23, 3876. [Google Scholar] [CrossRef]
  24. Jeon, S.O.; Lee, J.Y. Phosphine oxide derivatives for organic light emitting diodes. Mater. Chem. 2012, 22, 4233. [Google Scholar] [CrossRef]
  25. Jing, L.; Zhensong, Z.; Chunmiao, H.; Dongxue, D.; Zhao, Z.Y.; Huang, H.W.; Hui, X. Tuning peripheral group density in ternary phosphine oxide hosts for low-voltage-driven yellow PhOLEDs. J. Mater. Chem. C 2015, 3, 6709. [Google Scholar] [CrossRef]
  26. Dongdong, Z.; Juan, Q.; Zhang, Z.D.; Duan, L. Ultrahigh-Efficiency Green PHOLEDs with a Voltage under 3 V and a Power Efficiency of Nearly 110 lm W−1 at Luminance of 10 000 cd m−2. Adv. Mater. 2017, 29, 1702847. [Google Scholar] [CrossRef]
  27. Wenwen, T.; Qi, Q.; Bo, S.; Chang, Y.; Wei, J.; Xia, C.; Wei, S.; Huanga, H.; Yueming, S. A bipolar homoleptic iridium dendrimer composed of diphenylphosphoryl and diphenylamine dendrons for highly efficient non-doped single-layer green PhOLEDs. J. Mater. Chem. C 2015, 3, 981. [Google Scholar] [CrossRef]
  28. Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Highly efficient organic light-emitting diodes from delayed fluorescence. Nature 2012, 492, 234. [Google Scholar] [CrossRef]
  29. Ge, Z.; Hayakawa, T.; Ando, S.; Ueda, M.; Akiike, T.; Miyamoto, H.; Kajita, T.; Kakimoto, M.A. Spin-Coated Highly Efficient Phosphorescent Organic Light-Emitting Diodes Based on Bipolar Triphenylamine-Benzimidazole Derivatives. Adv. Funct. Mater. 2008, 18, 584. [Google Scholar] [CrossRef]
  30. Lee, S.Y.; Yasuda, T.; Yang, Y.S.; Zhang, Q.; Adachi, C. Luminous butterflies: Efficient exciton harvesting by benzophenone derivatives for full-color delayed fluorescence OLEDs. Angew. Chem. Int. Ed. 2014, 126, 6520. [Google Scholar] [CrossRef]
  31. Lee, C.W.; Lee, J.Y. Above 30% External Quantum Efficiency in Blue Phosphorescent Organic Light-Emitting Diodes Using Pyrido[2,3-b]indole Derivatives as Host Materials. Adv. Mater. 2013, 25, 5450. [Google Scholar] [CrossRef]
  32. Jiang, H. Hosts for High-Performance Phosphorescent Organic Light-Emitting Diodes Based on Carbazole Derivatives. J. Org. Chem. 2014, 3, 102. [Google Scholar] [CrossRef]
  33. Romero, D.H.; Schaer, M.; Leclerc, M.; Ades, D.; Siove, A.; Zuppiroli, L. The role of carbazole in organic light-emitting devices. Synthet. Met. 1996, 80, 271. [Google Scholar]
  34. Shahnawaz; Swayamprabha, S.S.; Nagar, M.R.; Yadav, R.A.K.; Gull, S.; Dubey, D.K.; Jou, J.H. Hole-transporting materials for organic light-emitting diodes: An overview. J. Mater. Chem. C 2019, 7, 7144. [Google Scholar] [CrossRef]
  35. An, Z.; Zhongfu, A.; Chao, Z.; Ye, T.; Runfeng, C.; Huifang, S.; Ting, C.; Zhixiang, W.; Huanhuan, L.; Renren, D.; et al. Stabilizing triplet excited states for ultralong organic phosphorescence. Nat. Mater. 2015, 14, 685. [Google Scholar] [CrossRef]
  36. Chengjian, C.; Zhenguo, C.; Kok, C.C.; Andrei, S.; Batsanov, S.; Zhan, Y.; Zhu, M.; Zhiyong, Y.; Bin, L. Carbazole isomer induces ultralong organic phosphorescence. Nat. Mater. 2015, 20, 175. [Google Scholar]
  37. Joule, J.A. Recent Advances in the Chemistry of 9H-Carbazoles. Adv. Heterocycl. Chem. 1984, 35, 84. [Google Scholar]
  38. Yang, T.; Xu, H.; Zhao, B.; Tao, P.; Sun, P.; Wang, H.; Xu, B.; Wong, W.Y. Three carbazole-based host materials: Facile synthesis, photophysical properties and performances in PhOLED. Tetrahedron 2016, 72, 8066. [Google Scholar] [CrossRef]
  39. Lade, J.; Lee, N.Y.; Patil, B.; Deshpande, Y.Y.; Pownthurai, B.; Hsieh, C.A.; Pingale, S.S.; Chen, L.Y.; Chaskar, A. Novel benzothiadiazine 1,1-dioxide based bipolar host materials for efficient red phosphorescent organic light emitting diodes. Org. Electron. 2021, 92, 106104. [Google Scholar] [CrossRef]
  40. Patil, B.; Pownthurai, B.; Chiou, S.S.; Chen, W.L.; Huang, D.C.; Jadhav, Y.; Chetti, P.; Chang, C.H.; Chaskar, A. Carbazole-pyridine pyrroloquinoxaline/benzothiadiazine 1,1-dioxide based bipolar hosts for efficient red PhOLEDs. Org. Electron. 2021, 96, 106217. [Google Scholar] [CrossRef]
  41. Wu, C.; Zhang, Y.; Ma, D.; Wang, Q. Phthalonitrile-based bipolar host for efficient green to red phosphorescent and TADF OLEDs. Dye Pigment. 2020, 173, 107895. [Google Scholar] [CrossRef]
  42. Im, Y.; Lee, J.Y. CN substituted indolocarbazole as a core structure of exciton harvesting and lifetime extending host for green thermally activated delayed fluorescent emitter. Dye Pigment. 2019, 164, 233. [Google Scholar] [CrossRef]
  43. Liu, X.Y.; Ge, H.T.; Zhao, Y.; Zhao, D.; Fan, J.; Liao, L.S. Novel carbazole derivatives designed by an ortho-linkage strategy for efficient phosphorescent organic light-emitting diodes. J. Mater. Chem. C 2018, 6, 4300. [Google Scholar] [CrossRef]
  44. Jiang, W.; Zhang, G.; Zhao, G.; Wang, X.; Tian, W.; Sun, Y. Novel benzonitrile-based AIE host with high triplet energy for highly efficient solution-processed blue TADF OLEDs. Dye Pigment. 2023, 210, 111037. [Google Scholar] [CrossRef]
  45. Gu, Y.; Zhu, L.; Li, Y.; Yu, L.; Wu, K.; Chen, T.; Huang, M.; Wang, F.; Gong, S.; Ma, D.; et al. Adamantane-Based Wide-Bandgap Host Material: Blue Electrophosphorescence with High Efficiency and Very High Brightness. Chem. Eur. J. 2015, 21, 98250. [Google Scholar] [CrossRef]
  46. Lee, K.H.; Kang, H.J.; Kim, H.M.; Seo, J.H.; Kim, Y.K.; Yoon, S.S. Pyridine/Isoquinoline-Carbazole Containing Bipolar Host Materials for Green Phosphorescent Organic Light-Emitting Diodes. J. Nanosci. Nanotechnol. 2011, 11, 1499. [Google Scholar] [CrossRef]
  47. Kautny, P.; Wu, Z.; Eichelter, J.; Horkel, E.; Stoger, B.; Chen, J.; Ma, D.; Frohlich, J.; Lumpi, D. Indolo[3,2,1-jk]carbazole based planarized CBP derivatives as host materials for PhOLEDs with low efficiency roll-off. Org. Electron. 2016, 34, 237. [Google Scholar] [CrossRef]
  48. Pan, B.; Wang, B.; Wang, Y.; Xu, P.; Wang, L.; Chen, J.; Ma, D. A simple carbazole-N-benzimidazole bipolar host material for highly efficient blue and single layer white phosphorescent organic light-emitting diodes. J. Mater. Chem. C 2014, 2, 2466. [Google Scholar] [CrossRef]
  49. Chang, S.Y.; Lin, G.T.; Cheng, Y.C.; Huang, J.J.; Chang, C.L.; Lin, C.F.; Lee, J.H.; Chiu, T.L.; Leung, M.K. Construction of Highly Efficient Carbazol-9-yl-Substituted Benzimidazole Bipolar Hosts for Blue Phosphorescent Light-Emitting Diodes: Isomer and Device Performance Relationships. ACS Appl. Mater. Interfaces 2018, 10, 42723. [Google Scholar] [CrossRef]
  50. Park, S.R.; Kim, S.M.; Kong, J.H.; Suh, M.C. Bipolar host materials with carbazole and dipyridylamine groups showing high triplet energy for blue phosphorescent organic light emitting diodes. Dye Pigment. 2017, 141, 217. [Google Scholar] [CrossRef]
  51. Park, S.R.; Seo, J.S.; Ahna, Y.; Lee, J.H.; Suh, M.C. Thermally stable benzo[f]quinoline based bipolar host materials for green phosphorescent OLEDs. Org. Electron. 2018, 63, 194. [Google Scholar] [CrossRef]
  52. Hung, W.I.; Tu, G.M.; Chen, S.W.; Chi, Y. Phenylcarbazole-dipyridyl triazole hybrid as bipolar host material for phosphorescent OLEDs. J. Mater. Chem. 2012, 22, 5410. [Google Scholar] [CrossRef]
  53. An, Z.F.; Chen, R.F.; Yin, J.; Xie, G.H.; Shi, H.F.; Tsuboi, T.; Huang, W. Conjugated Asymmetric Donor-Substituted 1,3,5-Triazines: New Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes. Chem. Eur. J. 2011, 17, 10871. [Google Scholar] [CrossRef]
  54. Wang, F.; Liu, D.; Li, J.; Ma, M. Molecular Engineering of Host Materials for High-Performance Phosphorescent OLEDs: Zig-Zag Conformation with 3D Gridding Packing Mode Facilitating Charge Balance and Quench Suppression. Adv. Funct. Mater. 2018, 28, 1803193. [Google Scholar] [CrossRef]
  55. Li, W.; Li, J.; Liu, D.; Jin, Q. Simple Bipolar Host Materials for High-Efficiency Blue, Green, and White Phosphorescence OLEDs. ACS Appl. Mater. Interfaces 2016, 8, 22382. [Google Scholar] [CrossRef]
  56. Zhang, T.; Zhu, M.; Li, J.; Zhang, Y.; Wang, X. Bipolar host materials comprising carbazole, pyridine and triazole moieties for efficient and stable phosphorescent OLEDs. Dye Pigment. 2021, 192, 109426. [Google Scholar] [CrossRef]
  57. Jeon, S.K.; Thirupathaiah, B.; Kim, C.; Lim, K.T.; Lee, J.Y.; Seo, S.Y. Novel carbazole derivative as a host material for blue phosphorescent organic light-emitting diodes. Dye Pigment. 2015, 114, 146. [Google Scholar] [CrossRef]
  58. Seo, C.; Choi, J.M.; Hong, S.S.; Lee, J.Y.; Seo, S.Y. Synthesis of novel benzothiophene derivative as a host material for blue phosphorescent organic light-emitting diodes. Dye Pigment. 2017, 136, 145. [Google Scholar] [CrossRef]
  59. Mao, H.T.; Song, W.L.; Zang, C.X.; Li, G.F.; Shan, G.G.; Sun, H.Z.; Xie, W.F.; Su, Z.M. Manipulating charge carrier transporting of disubstituted phenylbenzoimidazole-based host materials for efficient full-color PhOLEDs. Org. Electron. 2020, 77, 105513. [Google Scholar] [CrossRef]
  60. Zhuang, J.; Li, W.; Su, W.; Zhou, M.; Cui, Z. Novel ternary bipolar host material with carbazole, triazole and phosphine oxide moieties for high efficiency sky-blue OLEDs. New J.Chem. 2014, 38, 650. [Google Scholar] [CrossRef]
  61. Fan, C.; Zhao, F.; Gan, P.; Yang, S.; Liu, T.; Zhong, C.; Ma, D.; Qin, J.; Yang, C. Simple Bipolar Molecules Constructed from Biphenyl Moieties as Host Materials for Deep-Blue Phosphorescent Organic Light-Emitting Diodes. Chem. Eur. J. 2012, 18, 5510. [Google Scholar] [CrossRef] [PubMed]
  62. Maheshwaran, A.; Sree, V.G.; Park, H.Y.; Kim, H.; Han, S.H.; Lee, J.Y.; Jin, S.H. High Efficiency Deep-Blue Phosphorescent Organic Light-Emitting Diodes with CIE x, y (≤0.15) and Low Efficiency Roll-Off by Employing a High Triplet Energy Bipolar Host Material. Adv. Funct. Mater. 2018, 28, 1802945. [Google Scholar] [CrossRef]
  63. Park, I.S.; Seo, H.; Tachibana, H.; Kim, J.U.; Zhang, J.; Son, S.M.; Yasuda, T. Cyclohexane-coupled bipolar host materials with high triplet energies for organic light-emitting diodes based on thermally activated delayed fluorescence. ACS Appl. Mater. Interfaces 2017, 9, 2693–2700. [Google Scholar] [CrossRef] [PubMed]
  64. Lee, A.H.; Lee, J.; Lee, J.; Han, W.S. Silicon-based carbazole and oxadiazole hybrid as a bipolar host material for phosphorescent organic light-emitting diodes. Org. Electron. 2016, 38, 222. [Google Scholar] [CrossRef]
  65. Gohg, S.; Chen, Y.; Zhang, X.; Cai, P.; Zhong, C.; Ma, D.; Qin, J.; Yang, C.J. High-performance blue and green electrophosphorescence achieved by using carbazole-containing bipolar tetraarylsilanes as host materials. Mater. Chem. 2011, 21, 11197. [Google Scholar] [CrossRef]
  66. Yun, J.H.; Ha, J.S.; Lee, Y.; Kang, S.W.; Choo, C.; Lee, K.H.; Kim, J.M.; Lee, J.Y.; Jeon, S.O.; Bae, H.J.; et al. More than 25,000 h device lifetime in blue phosphorescent organic light-emitting diodes via fast triplet up-conversion of n-type hosts with sub μs triplet exciton lifetime. Chem. Eng. J. 2022, 450, 137974. [Google Scholar] [CrossRef]
  67. Ha, J.; Lim, J.; Lee, J.Y. A novel benzo[4,5]furo[3,2-d]pyrimidine-based host as a n-type host for blue phosphorescent organic light-emitting diodes. Sci. China Mater. 2022, 65, 1028. [Google Scholar] [CrossRef]
  68. Lin, C.C.; Huang, M.J.; Chiu, M.J.; Huang, M.P.; Chang, C.C.; Liao, C.Y.; Chiang, K.M.; Shiau, Y.J.; Chou, T.Y.; Chu, L.K.; et al. Molecular Design of Highly Efficient Thermally Activated Delayed Fluorescence Hosts for Blue Phosphorescent and Fluorescent Organic Light-Emitting Diodes. Chem. Mater. 2017, 29, 1527. [Google Scholar] [CrossRef]
  69. Hu, M.; Xu, Q.; Jiang, Y.; Mu, H.; Gao, L.; Hu, P.; Huang, J.; Su, J. Bipolar carbazole/quinoxaline-based host materials for efficient red PhOLEDs. Dye Pigment. 2018, 150, 185. [Google Scholar] [CrossRef]
  70. Peng, L.; Huo, Y.; He, S.; Liu, Y.; Ren, Z.; Ying, S.; Yan, S. A linear deep-blue bipolar fluorescent material with the CIEy < 0.065 serving as the emitter and host for high-performance monochromatic and hybrid white OLEDs. J. Mater. Chem. C 2022, 10, 11642. [Google Scholar] [CrossRef]
  71. Guo, S.; Zhou, H.; Wang, G.; Jin, X.; Zhang, Y.; Huang, J.; Cui, J.; Cao, J.; Miao, Y.; Wang, H.; et al. Novel benzonitrile- and benzo[d]imidazole-based bipolar hosts for green PhOLEDs with a low turn-on voltage. Dye Pigment. 2022, 200, 110041. [Google Scholar] [CrossRef]
  72. Jiang, W.; Duan, L.; Qiao, J.; Zhang, D.; Dong, G.; Wang, L.; Qiu, Y. Novel star-shaped host materials for highly efficient solution-processed phosphorescent organic light-emitting diodes. J. Mater. Chem. 2010, 20, 6131. [Google Scholar] [CrossRef]
  73. Wang, H.; Liub, Y.; Hu, W.; Xu, W.; Wang, P.; Wang, Y.; Luan, X. Novel spironaphthalenone-based host materials for efficient red phosphorescent and thermally activated delayed fluorescent OLEDs. Org. Electron. 2018, 61, 376. [Google Scholar] [CrossRef]
  74. Moon, B.J.; Yook, K.S.; Lee, J.Y.; Shin, S.; Hwang, S.H. Synthesis, photophysical and electro-optical properties of bis-carbazolyl methane based host material for pure-blue phosphorescent OLED. J. Luminance 2012, 132, 2557. [Google Scholar] [CrossRef]
  75. Chang, C.H.; Grinienė, R.; Su, Y.D.; Yeh, C.C.; Kao, H.C.; Grazulevicius, J.V.; Volyniuk, D.; Grigalevicius, S. Efficient red phosphorescent OLEDs employing carbazole-based materials as the emitting host. Dye Pigment. 2015, 122, 257. [Google Scholar] [CrossRef]
  76. Jeon, J.H.; Lee, N.J.; Lee, J.H.; Suh, M.C. Thermally-stable 2,3-diphenylated benzotiophene containing host materials for red phosphorescent organic light-emitting diodes. Dye Pigment. 2014, 111, 116. [Google Scholar] [CrossRef]
  77. Yoon, J.; Lee, C.; Park, S.H.; Kang, D.W.; Kim, H.; Jeong, J.E.; Woo, H.Y.; Hong, C.S.; Park, S.; Cho, M.J.; et al. Pyrimidine-based bipolar host materials for high efficiency solution processed green thermally activated delayed fluorescence OLEDs. J. Mater. Chem. C 2020, 8, 2196. [Google Scholar] [CrossRef]
  78. Zhang, D.; Cai, M.; Bin, Z.; Zhang, Y.; Zhang, D.; Duan, L. Highly efficient blue thermally activated delayed fluorescent OLEDs with record-low driving voltages utilizing high triplet energy hosts with small singlet–triplet splittings. Chem. Sci. 2016, 7, 3355. [Google Scholar] [CrossRef]
  79. Jeong, S.H.; Seo, C.W.; Lee, J.Y.; Cho, N.S.; Kim, J.K.; Yang, J.H. Comparison of Bipolar Hosts and Mixed-Hosts as Host Structures for Deep-Blue Phosphorescent Organic Light Emitting Diodes. Chem. Asian J. 2011, 6, 2895. [Google Scholar] [CrossRef]
  80. Fei, X.; Zhang, Y.J.; Liu, X.Y.; Fung, M.K.; Fan, J. A series of fluorenone-carbazole based regioisomers as bipolar host materials for efficient organic light emitting diodes. Tertahedron 2019, 75, 2664. [Google Scholar] [CrossRef]
  81. Jung, J.W.; Lee, K.M.; Kim, O.Y.; Lee, J.Y.; Hwang, S.H. Synthesis of a dibenzothiophene/carboline/carbazole hybrid bipolar host material for green phosphorescent OLEDs. Synth. Met. 2016, 213, 7. [Google Scholar] [CrossRef]
  82. Song, W.; Su, J. [1,2,4]Triazolo[1,5-a]pyridine based host materials for high-performance red PhOLEDs with external quantum efficiencies over 23%. J. Luminescence 2019, 206, 386. [Google Scholar] [CrossRef]
  83. Jeon, I.M.; Lee, I.H.; Lee, H.S.; Gong, M.S. Orange phosphorescent organic light-emitting diodes based on spirobenzofluorene type carbazole derivatives as a host material. Dye Pigment. 2011, 89, 29. [Google Scholar] [CrossRef]
  84. Zhao, X.; Wu, Y.; Shi, N.; Li, X.; Zhao, Y.; Sun, M.; Ding, D.; Xu, H.; Xie, L. Carbazole-endcapped Spiro[fluorene-9,9′-xanthene] with Large Steric Hindrance as Hole-transporting Host for Heavily-doped and High Performance OLEDs. Chin. J. Chem. 2015, 33, 955. [Google Scholar] [CrossRef]
  85. Quinton, C.; Thiery, S.; Jeannin, O.; Tondelier, D.; Geffroy, B.; Jacques, E.; Rault-Berthelot, J.; Poriel, C. Electron-Rich 4-Substituted Spirobifluorenes: Toward a New Family of High Triplet Energy Host Materials for High-Efficiency Green and Sky Blue Phosphorescent OLEDs. ACS Appl. Mater. Interfaces 2017, 9, 6194. [Google Scholar] [CrossRef]
  86. Zhang, Y.X.; Zhang, L.; Cui, L.S.; Gao, C.H.; Chen, H.; Li, Q.; Jiang, Z.Q.; Liao, L.S. Control of Conjugation Degree via Position Engineering to Highly Efficient Phosphorescent Host Materials. Org. Lett. 2014, 16, 3748. [Google Scholar] [CrossRef]
  87. Sun, B.; Tong, K.N.; Liu, S.N.; Fung, M.K.; Fan, J. A series of novel host materials based on the 10,11-dihydro-5H-dibenzo[b,f]azepine unit for highly efficient green and red organic light-emitting diodes. J. Mater. Chem. C 2021, 9, 2969. [Google Scholar] [CrossRef]
  88. Kim, J.; Kim, S.H.; Lee, H.W.; Lee, S.E.; Kim, Y.K.; Yoon, S.S. Bipolar Host Materials with Carbazole and Isoquinoline/Benzothiazole Moieties for Green Phosphorescent Organic Light-Emitting Diodes. J. Nanosci. Nanotechnol. 2016, 16, 10792. [Google Scholar] [CrossRef]
  89. Zhang, Z.; Xie, J.; Wang, Z.; Shen, B.; Wang, H.; Li, M.; Zhanga, J.; Cao, J. Manipulation of electron deficiency of δ-carboline derivatives as bipolar hosts for blue phosphorescent organic light-emitting diodes with high efficiency at 1000 cd m−2. J. Mater. Chem. C 2016, 4, 4226. [Google Scholar] [CrossRef]
  90. Wang, Z.; Zhu, J.; Liu, Z.; Wu, P.; Wang, H.; Zhanga, Z.; Wei, B. Thermally activated delayed fluorescence of co-deposited copper(i) complexes: Cost-effective emitters for highly efficient organic light-emitting diodes. J. Mater. Chem. C 2017, 5, 6982. [Google Scholar] [CrossRef]
  91. Im, Y.; Lee, J.Y. Effect of the position of nitrogen in pyridoindole on photophysical properties and device performances of α-, β-, γ-carboline based high triplet energy host materials for deep blue devices. Chem. Commun. 2013, 49, 5948. [Google Scholar] [CrossRef]
  92. Li, J.; Dong, S.C.; Opitz, A.; Liao, L.S.; Koch, N. Design principles of carbazole/dibenzothiophene derivatives as host material in modern efficient organic light-emitting diodes. J. Mater. Chem. C 2017, 5, 6989. [Google Scholar] [CrossRef]
  93. Godumala, M.; Yoon, J.; Jeong, C.H.; Lee, C.; Jeong, J.E.; Park, S.; Woo, H.Y.; Cho, M.J.; Choi, D.H. An excellent bipolar host material exhibiting EQE of 24.0% with small efficiency roll-off in solution-processable thermally activated delayed fluorescence OLEDs. J. Mater. Chem. C 2019, 7, 13930. [Google Scholar] [CrossRef]
  94. Wang, S.; Lee, C.W.; Lee, J.Y.; Hwang, S.H. Synthesis and green phosphorescent OLED device performance of cyanofluorene-linked phenylcarbazoles as host material. J. Chem. 2018, 42, 5059. [Google Scholar] [CrossRef]
  95. Guichen, Y.; Yin, M.; Zhu, J.; Zhou, H.; Miao, Y.; Huang, J.; Wang, H.; Su, J. Novel difluorenyl substituted 1,3,5-triazine and carbazole based bipolar host materials with high thermal stability for efficient green phosphorescent organic light-emitting diodes (PhOLEDs). Tetrahedron 2021, 90, 132175. [Google Scholar] [CrossRef]
  96. Seo, J.A.; Jeon, S.K.; Lee, J.Y. Acridine derived stable host material for long lifetime blue phosphorescent organic light-emitting diodes. Org. Electron. 2016, 34, 33. [Google Scholar] [CrossRef]
  97. Grigalevicius, S.; Tavgeniene, D.; Krucaite, G.; Blazevicius, D.; Griniene, R.; Lai, Y.N.; Chiu, H.H.; Chang, C.H. Efficient blue and green phosphorescent OLEDs with host material containing electronically isolated carbazolyl fragments. Opt. Mater. 2018, 79, 446. [Google Scholar] [CrossRef]
  98. Liang, X.; Liu, Z.; Xia, Y.; Li, D.; Li, J.; Wang, H.; Zhang, Z.; Wang, S.; Zhao, B.; Li, Z.; et al. Lifting Triplet Energy and Bipolar Characteristics by Limiting theRotation of the Peripheral Groups in Host Materials to Achieve High-Efficiency Blue OLED. Chem. Asian J. 2022, 17, 1. [Google Scholar] [CrossRef]
  99. Xie, G.; Wang, J.; Cao, Y.; Xue, X.; Zhang, X.; Liu, C.; Li, H.; Tao, Y.; Chen, R. Phosphine Sulfide-Based Bipolar Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes. Molecules 2021, 26, 4079. [Google Scholar] [CrossRef]
  100. Zhao, Z.; Yu, G.; Chang, Q.; Liu, X.; Liu, Y.; Wang, L.; Liu, Z.; Bian, Z.; Liu, W.; Huang, C. Carbazolylphosphines and carbazolylphosphine oxides: Facilely synthesized host materials with tunable mobilities and high triplet energy levels for blue phosphorescent OLEDs. J. Mater. Chem. C 2017, 5, 7344. [Google Scholar] [CrossRef]
  101. Cho, Y.J.; Lee, J.Y. Modified N,N′-Dicarbazolyl-3,5-benzene as a High Triplet Energy Host Material for Deep-Blue Phosphorescent Organic Light-Emitting Diodes. Chem. Eur. J. 2011, 17, 11415. [Google Scholar] [CrossRef] [PubMed]
  102. Li, C.; Fan, X.; Han, C.; Xu, H. A ternary phosphine oxide host featuring thermally activated delayed fluorescence for blue PHOLEDs with >20% EQE and extremely low roll-offs. J. Mater. Chem. C 2018, 6, 6747. [Google Scholar] [CrossRef]
  103. Zhou, H.; Wang, G.; Guo, S.; Jin, X.; Luo, X.; Miao, Y.; Huang, J.; Wang, H.; Su, J. A universal bipolar host based on isonicotinonitrile and carbazole for efficient red, green and blue PhOLEDs. New J. Chem. 2022, 46, 15344. [Google Scholar] [CrossRef]
  104. Cho, Y.J.; Yook, K.S.; Lee, J.Y. A Universal Host Material for High External Quantum Efficiency Close to 25% and Long Lifetime in Green Fluorescent and Phosphorescent OLEDs. Adv. Mater. 2014, 26, 4050. [Google Scholar] [CrossRef]
  105. Lee, D.R.; Lim, J.; Lee, J.Y. Phthalonitrile based charge transfer type host for yellow phosphorescent organic light-emitting diodes. Org. Electron. 2021, 94, 106166. [Google Scholar] [CrossRef]
  106. Li, S.W.; Yu, C.H.; Ko, C.L.; Chatterjee, T.; Hung, W.Y.; Wong, K.T. Cyanopyrimidine-Carbazole Hybrid Host Materials for High-Efficiency and Low-Efficiency Roll-Off TADF OLEDs. ACS Appl. Mater. Interfaces 2018, 10, 12930. [Google Scholar] [CrossRef] [PubMed]
  107. Kim, M.; Jeon, S.K.; Lee, J.Y. Molecular design approach of increasing the triplet energy of host materials using pyrrole as a core structure. RCS. Adv. 2015, 5, 100378. [Google Scholar] [CrossRef]
  108. Lu, C.W.; Tsai, C.C.; Li, W.C.; Chiu, T.Y. Triarylboryl-substituted carbazoles as bipolar host materials for efficient green phosphorescent organic light-emitting devices. Dye Pigment. 2019, 163, 145. [Google Scholar] [CrossRef]
  109. Choi, H.J.; Kim, B.S.; Kim, O.; Chin, B.D.; Lee, C.W. The Correlation between Structure and Physical Properties of Soluble Host for Blue Phosphorescent OLED. Korean Phys. Soc. 2019, 74, 1176. [Google Scholar]
  110. Lee, C.W.; Lee, J.Y. High quantum efficiency and color stability in white phosphorescent organic light emitting diodes using a pyridine modified carbazole derivative. Dye Pigment. 2014, 103, 34. [Google Scholar] [CrossRef]
  111. Song, W.; Shi, L.; Gao, L.; Hu, P.; Mu, H.; Xia, Z.; Huang, J.; Su, J. [1,2,4]Triazolo[1,5-a]pyridine as Building Blocks for Universal Host Materials for High-Performance Red, Green, Blue and White Phosphorescent Organic Light-Emitting Devices. ACS Appl. Mater. Interface 2018, 10, 5714. [Google Scholar] [CrossRef] [PubMed]
  112. Huang, J.J.; Hung, Y.H.; Ting, P.L.; Tsai, Y.N.; Gao, H.J.; Chiu, T.L.; Lee, J.H.; Chen, C.L.; Chou, P.T.; Leung, M.-T. Orthogonally Substituted Benzimidazole-Carbazole Benzene As Universal Hosts for Phosphorescent Organic Light-Emitting Diodes. Org. Lett. 2016, 18, 672. [Google Scholar] [CrossRef] [PubMed]
  113. Chen, D.; He, W.Z.; Liao, H.S.; Hu, Y.X.; Xie, D.D.; Wang, B.Y.; Chi, H.J.; Lv, Y.L.; Zhu, X.; Li, X. Benzimidazole/carbazole-based bipolar host materials for highly efficient green phosphorescent OLEDs with negligible efficiency roll-off. Org. Electron. 2023, 113, 106715. [Google Scholar] [CrossRef]
  114. Reddy, M.R.; Han, S.H.; Lee, J.Y.; Seo, S.Y. Synthesis and characterization of quinoxaline derivative for high performance phosphorescent organic light-emitting diodes. Dye Pigment. 2018, 153, 132. [Google Scholar] [CrossRef]
  115. Chen, Z.; Li, H.; Tao, Y.; Chen, L.; Chen, C.; Jiang, H.; Xu, S.; Zhou, X.; Chen, R.; Huang, W. Tuning Intramolecular Conformation and Packing Mode of Host Materials through Noncovalent Interactions for High-Efficiency Blue Electrophosphorescence. ACS Omega. 2019, 4, 9129. [Google Scholar] [CrossRef]
  116. Hudson, Z.M.; Michael, Z.W.; Helander, H.; Lu, H.Z.; Wang, S. N -Heterocyclic Carbazole-Based Hosts for Simplifi ed Single-Layer Phosphorescent OLEDs with High Effi ciencies. Adv. Mater. 2012, 24, 2922. [Google Scholar] [CrossRef]
  117. Zhong, Q.; Zeng, S.; Fan, P.; Pang, Y.; Zhu, W.; Wang, Y. Effective bipolar hosts prepared via dipole moment engineering for phosphorescent emitters and white OLEDs. J. Mater. Chem. C 2022, 10, 18415. [Google Scholar] [CrossRef]
  118. Byeon, S.Y.; Choi, J.M.; Lee, J.Y. Pyridoindole based intramolecular charge transfer type host material for blue phosphorescent organic light-emitting diodes. Dye Pigment. 2016, 134, 285. [Google Scholar] [CrossRef]
  119. Tao, Y.; Guo, X.; Hao, L.; Chen, R.; Li, H.; Chen, Y.; Zhang, X.; Lai, W.; Huang, W. A Solution-Processed Resonance Host for Highly Efficient Electrophosphorescent Devices with Extremely Low Efficiency Roll-off. Adv. Mater. 2015, 27, 6939. [Google Scholar] [CrossRef]
  120. Huang, J.J.; Yun, L.K.; Kung, T.J.; Chen, C.L.; Lee, J.H.; Wu, Y.R.; Chiu, T.L.; Chou, P.T.; Leung, M. Networking hole and electron hopping paths by Y-shaped host molecules: Promoting blue phosphorescent organic light emitting diodes. J. Mater. Chem. C 2017, 5, 3600. [Google Scholar] [CrossRef]
  121. Wen, H.Y.; Ho, S.Y. A bipolar host material for the construction of triplet-energy level for white phosphorescent organic light emitting diodes. RSC Adv. 2022, 12, 28128. [Google Scholar] [CrossRef]
  122. Yao, C.; Cui, Q.; Peng, J.; Xu, X.; Liu, R.; Wang, J.; Tian, Y.; Li, L. Solution processed blue phosphorescent organic light emitting diodes using a Ge-based small molecular host. J. Mater. Chem. C 2015, 3, 5017. [Google Scholar] [CrossRef]
  123. Choi, S.; Godumala, M.; Lee, J.H.; Kim, G.H.; Moon, J.S.; Kim, J.Y.; Yoon, D.W.; Yang, J.H.; Kim, J.; Cho, M.J.; et al. Optimized structure of silane-core containing host materials for highly efficient blue TADF OLEDs. J. Mater. Chem. C 2017, 5, 6570. [Google Scholar] [CrossRef]
  124. Yun, J.H.; Lim, J.; Chung, W.J.; Lee, J.Y. Exciton stabilizing high triplet energy n-type hosts for blue phosphorescent organic light-emitting diodes. Dye Pigment. 2021, 190, 109297. [Google Scholar] [CrossRef]
  125. Choi, S.; Yoon, J.W.; Godumala, M.; Kim, H.J.; Park, S.H.; Kim, S.K.; Lee, H.; Kwon, J.H.; Cho, M.J.; Choi, D.H. 2D-σ-2A type cruciform host material with silane core for highly efficient solution-processable green thermally activated delayed fluorescence organic light emitting diodes. Dye Pigment. 2019, 167, 120. [Google Scholar] [CrossRef]
  126. Liu, H.; Bai, Q.; Yao, L.; Hu, D.; Tang, X.; Shen, F.; Zhang, H.; Gao, Y.; Lu, P.; Yang, B.; et al. Solution-Processable Hosts Constructed by Carbazole/PO Substituted Tetraphenylsilanes for Efficient Blue Electrophosphorescent Devices. Adv. Funct. Mater. 2014, 24, 5881. [Google Scholar] [CrossRef]
  127. Chou, H.H.; Cheng, C.H. A highly efficient universal bipolar host for blue, green, and red phosphorescent OLEDs. Adv. Mater. 2010, 22, 2468. [Google Scholar] [CrossRef]
  128. Gudeika, D.; Bezvikonnyi, O.; Masimukku, N.; Volyniuk, D.; Chen, C.H.; Ding, W.C.; Lee, J.H.; Chiu, T.L.; Grazulevicius, J.V. Tetraphenyl ornamented carbazolyl disubstituted diphenyl sulfone as bipolar TADF host for highly efficient OLEDs with low efficiency roll-offs. Dye Pigment. 2021, 194, 109573. [Google Scholar] [CrossRef]
  129. Yan, X.; Cheng, Z.; Yang, T.; Li, C.; Wang, Y. Carbazole-benzonitrile based organic semiconductors: Synthesis, characterization and electroluminescent property. Org. Electron. 2022, 102, 106445. [Google Scholar] [CrossRef]
  130. Li, W.; Li, J.; Liu, D.; Wang, F.; Zhang, S. Bipolar host materials for high-efficiency blue phosphorescent and delayed-fluorescence OLEDs. J. Mater. Chem. C 2015, 3, 12529. [Google Scholar] [CrossRef]
  131. Su, S.J.; Sasabe, H.; Takeda, T.; Kido, J. Pyridine-Containing Bipolar Host Materials for Highly Efficient Blue Phosphorescent OLEDs. Chem. Mater. 2008, 20, 1691. [Google Scholar] [CrossRef]
  132. Yu, J.G.; Han, S.H.; Jeon, H.R.; Chung, H.K.; Lee, J.Y. Pyridazine derived bipolar host materials for phosphorescent organic light-emitting diodes. J. Luminescence 2018, 194, 33. [Google Scholar] [CrossRef]
  133. Liu, D.; Li, D.; Wang, M.; Li, W. 1,2,4-Triazole-containing bipolar hosts for blue and green phosphorescent organic light-emitting diodes. J. Mater. Chem. C 2016, 4, 7260. [Google Scholar] [CrossRef]
  134. Wang, Y.; Song, W.; Chen, Y.; Jiang, Y.; Mu, H.; Huang, J.; Su, J. A series of new bipolar CBP derivatives with introduction of a electron-deficient moiety for efficient green organic light-emitting diodes. Org. Electron. 2018, 61, 142. [Google Scholar] [CrossRef]
  135. Jang, H.G.; Soon, W.; Lee, J.Y.; Heang, S.H. Synthesis of pyrimidine-cored host materials bearing phenylcarbazole for efficient yellow phosphorescent devices: Effect of linkage position. RSC Adv. 2015, 5, 17030. [Google Scholar] [CrossRef]
  136. Zhuang, J.; Su, W.; Li, W.; Zhou, Y.; Shen, Q.; Zhou, M. Configuration effect of novel bipolar triazole/carbazole-based host materials on the performance of phosphorescent OLED devices. Org. Electron. 2012, 13, 2210. [Google Scholar] [CrossRef]
  137. Song, W.; Chen, Y.; Xu, Q.; Mu, H.; Cao, J.; Huang, J.; Su, J. [1,2,4]Triazolo[1,5-a]pyridine-Based Host Materials for Green Phosphorescent and Delayed-Fluorescence OLEDs with Low Efficiency Roll-Off. ACS Appl. Mater. Interfaces 2018, 10, 24689. [Google Scholar] [CrossRef]
  138. Gong, S.; Zhao, Y.; Yang, C.; Zhong, C.; Qin, J.; Ma, D. Tuning the Photophysical Properties and Energy Levels by Linking Spacer and Topology between the Benzimidazole and Carbazole Units: Bipolar Host for Highly Efficient Phosphorescent OLEDs. J. Phys. Chem. C 2010, 114, 5193. [Google Scholar] [CrossRef]
  139. Li, Q.; Cui, L.S.; Zhong, C.; Yuan, X.D.; Dong, S.H.; Jiang, Z.Q.; Liao, L.S. Synthesis of new bipolar host materials based on 1,2,4-oxadiazole for blue phosphorescent OLEDs. Dye Pigment. 2014, 101, 142. [Google Scholar] [CrossRef]
  140. Li, Q.; Cui, L.S.; Zhong, C.; Jiang, Z.Q.; Liao, L.S. Asymmetric Design of Bipolar Host Materials with Novel 1,2,4-Oxadiazole Unit in Blue Phosphorescent Device. Org. Lett. 2014, 16, 1622. [Google Scholar] [CrossRef]
  141. Tao, Y.; Wang, Q.; Yang, C.; Zhong, C.; Zhang, K.; Qin, J.; Ma, D. Tuning the Optoelectronic Properties of Carbazole/Oxadiazole Hybrids through Linkage Modes: Hosts for Highly Efficient Green Electrophosphorescence. Adv. Funct. Mater. 2010, 20, 304. [Google Scholar] [CrossRef]
  142. Kaunty, P.; Wu, Z.; Stoer, B.; Tissot, A.; Horkel, E.; Chen, J.; Ma, D.; Hagemann, H.; Frohlich, J.; Lumpi, D. Controlling singlet–triplet splitting in carbazole–oxadiazole based bipolar phosphorescent host materials. Org. Electron. 2015, 17, 216. [Google Scholar] [CrossRef]
  143. Tsik, U.; Volyniuk, D.; Andruleviciene, V.; Leitonas, K.; Sych, G.; Bezvikonnyi, O.; Jasinskas, V.; Gulbinas, V.; Stakhira, P.; Grazulevicius, J.V. Triphenylamino or 9-phenyl carbazolyl-substituted pyrimidine-5-carbonitriles as bipolar emitters and hosts with triplet harvesting abilities. Mater. Today. Chem. 2022, 25, 100955. [Google Scholar] [CrossRef]
  144. Yao, C.; Peng, C.; Yang, Y.; Li, L.; Bo, M.; Wang, J. Larger VH (Hole Distribution Volume)/VM (Molecular Volume) Induced Higher Charge Mobility of Group IVA Element-Based Host Materials for Potentially Highly Efficient Blue OLEDs. J. Phys. Chem. C 2018, 122, 22273. [Google Scholar] [CrossRef]
  145. Kim, D.; Coropceanu, V.; Bredas, J.L. Design of Efficient Ambipolar Host Materials for Organic Blue Electrophosphorescence: Theoretical Characterization of Hosts Based on Carbazole Derivatives. J. Am. Chem. Soc. 2011, 133, 17895. [Google Scholar] [CrossRef]
  146. Seo, J.; Park, S.R.; Kim, M.; Suh, M.C.; Lee, J. The role of electron-transporting Benzo[f]quinoline unit as an electron acceptor of new bipolar hosts for green PHOLEDs. Dye Pigment. 2019, 162, 959. [Google Scholar] [CrossRef]
  147. Cui, L.S.; Kim, J.U.; Nomura, H.; Nakanotani, H.; Adachi, C. Benzimidazobenzothiazole-Based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light-Emitting Diodes. Angew.Chem. Int. Ed. 2016, 55, 6864. [Google Scholar] [CrossRef]
  148. Cha, J.R.; Lee, C.W.; Gong, M.S. Bipolar Host Material for Phosphorescent OLEDs Based on 2,7-Diazacarbazole as a New Electron-transporting Unit. Bull. Korean Chem. Soc. 2017, 38, 1016. [Google Scholar] [CrossRef]
  149. Cho, M.J.; Kim, S.J.; Yoon, S.H.; Shin, J.; Hong, T.R.; Kim, H.J.; Son, Y.H.; Kang, J.S.; Um, H.A.; Lee, T.W.; et al. New Bipolar Host Materials for Realizing Blue Phosphorescent Organic Light-Emitting Diodes with High Efficiency at 1000 cd/m2. ACS Appl. Mater. Interfaces 2014, 6, 19808. [Google Scholar] [CrossRef]
  150. Kang, J.K.; Hong, T.R.; Kim, H.J.; Son, Y.H.; Bin, J.K.; Lee, B.S.; Yang, J.H.; Kim, J.W.; Cho, M.J.; Kwon, J.H.; et al. Molecular design of large-bandgap host materials and their application to blue phosphorescent organic light-emitting diodes. Org. Electron. 2015, 26, 218. [Google Scholar] [CrossRef]
  151. Moon, J.S.; Ahn, D.H.; Kim, S.W.; Lee, S.Y.; Lee, J.Y.; Kwon, J.H. δ-Carboline-based bipolar host materials for deep blue thermally activated delayed fluorescence OLEDs with high efficiency and low roll-off characteristic. RSC Adv. 2018, 8, 17025. [Google Scholar] [CrossRef]
  152. Kang, J.S.; Hong, T.R.; Kim, H.J.; Son, Y.H.; Lampande, R.; Kang, B.Y.; Lee, C.; Bin, J.K.; Lee, B.S.; Yang, J.H.; et al. High-performance bipolar host materials for blue TADF devices with excellent external quantum efficiencies. J. Mater. Chem. C 2016, 4, 4512. [Google Scholar] [CrossRef]
  153. Lin, J.-S.; Lee, M.-T.; Chu, M.-T.; Tseng, M.-R. P-221L: Late-News Poster: New Blue Phosphorescent Host for High-efficiency White OLED. SID Int. Symp. Dig. Tech. Pap. 2011, 42, 1787. [Google Scholar] [CrossRef]
  154. Liu, K.; Li, X.L.; Liu, M.; Chen, D.; Cai, X.; Wu, Y.C.; Lo, C.C.; Lien, A.; Caoa, Y.; Su, S.J. 9,9-Diphenyl-thioxanthene derivatives as host materials for highly efficient blue phosphorescent organic light-emitting diodes. J. Mater. Chem. C 2015, 3, 9999. [Google Scholar] [CrossRef]
  155. Choi, K.H.; Kim, J.M.; Chung, W.J.; Lee, J.Y. Effects of Substitution Position of Carbazole-Dibenzofuran Based High Triplet Energy Hosts to Device Stability of Blue Phosphorescent Organic Light-Emitting Diodes. Molecules 2021, 26, 2804. [Google Scholar] [CrossRef] [PubMed]
  156. Kang, Y.J.; Jeon, S.K.; Lee, J.Y. A zig-zag type bidibenzofuran based host material for green phosphorescent organic light-emitting diodes. Dye Pigment. 2015, 114, 278. [Google Scholar] [CrossRef]
  157. Jiang, H.J.; Sun, J.; Yuan, K.; Zhang, Q.W. Synthesis and characterization of novel topology-varied compounds based on fluorene and carbazole: Potential host materials for phosphorescent organic light-emitting diodes. Synth. Met. 2014, 197, 217. [Google Scholar] [CrossRef]
  158. Li, G.; Zheng, J.; Klimes, K.; Zhu, Z.Q.; Wu, J.; Zhu, H.; Li, J. Novel Carbazole/Fluorene-Based Host Material for Stable and Efficient Phosphorescent OLEDs. ACS Appl. Mater. Interfaces 2019, 11, 40320. [Google Scholar] [CrossRef]
  159. Yu, Z.; Zhang, J.; Liu, S.; Zhang, L.; Zhao, Y.; Zhao, H.; Xie, W. High-Efficiency Blue Phosphorescent Organic Light-Emitting Devices with Low Efficiency Roll-Off at Ultrahigh Luminance by the Reduction of Triplet-Polaron Quenching. ACS Appl. Mater. Interfaces 2019, 11, 6292. [Google Scholar] [CrossRef]
  160. Lin, W.C.; Huang, W.C.; Huang, M.H.; Fan, C.C.; Lin, H.W.; Chen, L.Y.; Liu, Y.W.; Lin, J.S.; Chao, T.C.; Tseng, M.R. A bipolar host containing carbazole/dibenzothiophene for efficient solution-processed blue and white phosphorescent OLEDs. J. Mater. Chem. 2013, C 1, 6835. [Google Scholar]
  161. Bucinskas, A.; Bezvikonnyi, O.; Gudeika, D.; Volyniuk, D.; Grazulevicius, J.V. Methoxycarbazolyl-disubstituted dibenzofuranes as holes- and electronstransporting hosts for phosphorescent and TADF-based OLEDs. Dye Pigment. 2020, 172, 107781. [Google Scholar] [CrossRef]
  162. Keruckas, J.; Volyniuk, D.; Simokaitiene, J.; Narbutaitis, E.; Lazauskas, A.; Lee, P.H.; Chiu, T.L.; Lin, C.F.; Arsenyan, P.; Lee, J.H.; et al. Methoxy- and tert-butyl-substituted meta-bis(N-carbazolyl)phenylenes as hosts for organic light-emitting diodes. Org. Electron. 2019, 73, 317. [Google Scholar] [CrossRef]
  163. Tang, C.; Chen, J.; Li, Y.; Liu, X.; Zhang, L.; Wang, F.; Cao, X.; Jiang, T. Alkyl-Substituted Carbazole/Pyridine Hybrid Host Materials for Efficient Solution-Processable Blue- and Green-Emitting Phosphorescent OLEDs. Electron. Mater. Lett. 2021, 17, 148. [Google Scholar]
  164. Song, W.; Lee, H.L.; Lee, J.Y. High triplet energy exciplex hosts for deep blue phosphorescent organic light-emitting diodes. J. Mater. Chem. C 2017, 5, 5923. [Google Scholar] [CrossRef]
  165. Pei, J.; Du, X.; Li, C.; Wang, C.; Fan, C.; Tan, H.; Cao, B.; Huang, F.; Tao, S.; Li, J. Highly twisted organic molecules with ortho linkage as the efficient bipolar hosts for sky-blue thermally activated delayed fluorescence emitter in OLEDs. Org. Electron. 2017, 50, 153. [Google Scholar] [CrossRef]
  166. Hladka, I.; Lytvyn, R.; Volyniuk, D.; Gudeika, D.; Grazulevicius, J.V. W-shaped bipolar derivatives of carbazole and oxadiazole with high triplet energies for electroluminescent devices. Dye Pigment. 2018, 149, 812. [Google Scholar] [CrossRef]
  167. Tang, J.; Chen, Y.; Cong, L.; Lin, B.; Sun, Y. Novel tri-carbazole modified fluorene host material for highly efficient solution-processed blue and green electrophosphorescent devices. Tetrahedron 2014, 70, 3847. [Google Scholar] [CrossRef]
  168. Li, H.; Xu, L.; Tang, Y.; Tao, Y.; Xu, S.; Zheng, C.; Xing, G.; Zhou, X.; Huang, W.; Chen, R. Direct silicon–nitrogen bonded host materials with enhanced σ–π conjugation for blue phosphorescent organic light-emitting diodes. J. Mater. Chem. C 2016, 4, 10047. [Google Scholar] [CrossRef]
  169. Deng, L.; Wang, X.; Zhang, Z.; Li, J. Durene-decorated CBP derivatives as phosphorescent hosts and exciton-blocking materials for efficient blue OLEDs. J. Mater. Chem. 2012, 22, 19700. [Google Scholar] [CrossRef]
  170. Oner, S.; Oner, I.; Akdag, H.; Varlikli, C. Tetraphenylsilane group containing carbazoles as high triplet energy host materials for solution-processable PhOLEDs. Turk. J. Chem. 2015, 39, 917. [Google Scholar] [CrossRef]
  171. Hung, Y.T.; Chen, Z.Y.; Hung, W.Y.; Chen, D.G.; Wong, K.T. Exciplex Cohosts Employing Nonconjugated Linked Dicarbazole Donors for Highly Efficient Thermally Activated Delayed Fluorescence-Based Organic Light-Emitting Diodes. ACS Appl. Mater. Interfaces 2018, 10, 34435. [Google Scholar] [CrossRef] [PubMed]
  172. Yuan, J.; Jiang, H.; Yang, Q.; Xiang, Y.; Zhang, Y.; Dai, Y.; Li, P.; Zheng, C.; Xie, G.; Chen, R. A solution-processable wholly-aromatic bipolar host material for highly efficient blue electroluminescent devices. J. Mater. Chem. C 2021, 9, 687. [Google Scholar] [CrossRef]
  173. Cai, M.; Zhang, D.; Xu, J.; Hong, X.; Zhao, C.; Song, X.; Qiu, Y.; Kaji, H.; Duan, L. Unveiling the Role of Langevin and Trap-Assisted Recombination in Long Lifespan OLEDs Employing Thermally Activated Delayed Fluorophores. ACS Appl. Mater. Interfaces 2019, 11, 1096. [Google Scholar] [CrossRef] [PubMed]
  174. Choi, S.W.; Lee, J.Y.; Hwang, S.H. Synthesis of phenylcarbazole–thiophene-based structural isomers as unipolar host materials for blue PHOLEDs and their device performance. Org. Electron. 2014, 15, 1413. [Google Scholar] [CrossRef]
  175. Jia, B.; Lian, H.; Sun, T.; Wei, J.; Yang, J.; Zhou, H.; Huang, J.; Dong, Q. New bipolar host materials based on methyl substituted pyridazine for high-performance green and red phosphorescent OLEDs. Dye Pigment. 2019, 168, 212. [Google Scholar] [CrossRef]
  176. Macdonald, J.; O’Connell, J.; Weber, K.; Hirai, T.; Groarke, M.; Andresen, S.; Bown, M.; Ueno, K. A New Class of Host Materials for Blue Phosphorescent Organic Electroluminescent Devices; SID Symposium Digest of Technical Papers; Wiley: Hoboken, NJ, USA, 2012; DIGEST 447. [Google Scholar]
  177. Tian, G.; Wei, X.; Xiang, N.; Huang, J.; Cao, J.; Wang, Z.; Zhang, J.; Su, J. Small organic molecules based on oxazole/thiazole with excellent performances in green and red phosphorescent organic light-emitting diodes. RSC Adv. 2016, 6, 51575. [Google Scholar] [CrossRef]
  178. Wang, F.; Zhao, Y.; Xu, H.; Zhang, J.; Miao, Y.; Guo, K.; Shinar, R.; Shinar, J.; Wang, H.; Xu, B. Two novel bipolar hosts based on 1,2,4-triazole derivatives for highly efficient red phosphorescent OLEDs showing a small efficiency roll-off. Org. Electron. 2019, 70, 272. [Google Scholar] [CrossRef]
  179. Sun, J.; Jiang, H.J.; Zhang, J.L.; Tao, Y.; Chen, R.F. Synthesis and characterization of heteroatom substituted carbazole derivatives: Potential host materials for phosphorescent organic light-emitting diodes. J. Chem. 2013, 37, 977. [Google Scholar] [CrossRef]
  180. Vadagaonkar, K.S.; Yang, C.J.; Zeng, W.H.; Chen, J.H.; Patil, B.N.; Chetti, P.; Chen, L.Y.; Chaskar, A.C. Triazolopyridine hybrids as bipolar host materials for green phosphorescent organic light-emitting diodes (OLEDs). Dye Pigment. 2019, 160, 301. [Google Scholar] [CrossRef]
  181. Jang, H.G.; Kim, B.S.; Lee, J.Y.; Hwang, S.H. Synthesis of dimesitylborane-substituted phenylcarbazoles as bipolar host materials and the variation of the green PHOLED performance with the substituent position of the boron atom. Dalton. Trans. 2014, 43, 7712. [Google Scholar] [CrossRef]
  182. Li, W.; Li, J.; Wang, F.; Gao, Z.; Zhang, S. Universal Host Materials for High-Efficiency Phosphorescent and Delayed-Fluorescence OLEDs. ACS Appl. Mater. Interface 2015, 7, 26206. [Google Scholar] [CrossRef]
  183. Sun, M.; Zhu, L.; Kan, W.; Wei, Y.; Ma, D.; Fan, X.; Huang, W.; Xu, H. Ternary donor–acceptor phosphine oxide hosts with peculiar high energy gap for efficient blue electroluminescence. J. Mater. Chem. C 2015, 3, 9469. [Google Scholar] [CrossRef]
  184. Patil, B.N.; Lade, J.J.; Vadagaonkar, K.S.; Chetti, P.; Chaskar, A.C. Pyrrolo[1, 2-a]quinoxaline-Based Bipolar Host Materials for Efficient Red Phosphorescent OLEDs. Chem. Select. 2018, 3, 10010. [Google Scholar] [CrossRef]
  185. Yang, T.; Xu, H.; Wang, K.; Tao, P.; Wang, F.; Zhao, B.; Wang, H.; Xu, B. Bipolar host materials based on diphenylphosphine oxide and carbazole derivatives with high triplet energy: Synthesis, characterization and photoelectronic performance in PhOLEDs. Dye Pigment. 2018, 153, 67. [Google Scholar] [CrossRef]
  186. Huang, H.; Yang, X.; Pan, B.; Wang, L.; Chen, J.; Ma, D.; Yang, C. Benzimidazole–carbazole-based bipolar hosts for high efficiency blue and white electrophosphorescence applications. J. Mater. Chem. 2012, 22, 13223. [Google Scholar] [CrossRef]
  187. Huixia, X.; Fang, W.; Kexiang, W.; Yanqin, M.; Jie, L.; Jing, Z.; Hua, W.; Yuying, H.; Bingshe, X. Three acceptors based bipolar materials with tunable excited state natures and applications as non-doped blue emitters and hosts in OLEDs. Dye Pigment. 2018, 155, 84. [Google Scholar] [CrossRef]
  188. Dong, Q.; Tai, F.; Lian, H.; Chen, Z.; Hu, M.; Huang, J.; Wong, W.Y. Thermally stable bipolar host materials for high efficiency phosphorescent green and blue organic light-emitting diodes. Dye Pigment. 2017, 143, 470. [Google Scholar] [CrossRef]
  189. Park, J.H.; Kim, E.K.; Deeb, I.M.E.; Jung, S.J.; Choi, D.H.; Kim, D.H.; Yoo, K.H.; Kwon, J.H.; Lee, S.H. New Bipolar Green Host Materials Containing Benzimidazole-Carbazole Moiety in Phosphorescent OLEDs. Bull. Korean Chem. Soc. 2011, 32, 3841. [Google Scholar] [CrossRef]
  190. Byeon, S.Y.; Kim, J.H.; Lee, J.Y. CN-Modified Host Materials for Improved Efficiency and Lifetime in Blue Phosphorescent and Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes. ACS Appl. Mater. Interfaces 2017, 9, 13339. [Google Scholar] [CrossRef]
  191. Jia, B.; Lian, H.; Sun, T.; Guo, H.; Cheng, X.; Wu, J.; Chen, Y.; Dong, Q.; Huang, J. Efficient green phosphorescent organic light-emitting diodes enabled with new and thermally stable carbazole/pyridine derivatives as hosts. Dye Pigment. 2018, 159, 298. [Google Scholar] [CrossRef]
  192. Kim, S.M.; Yun, J.H.; Byeon, S.Y.; Jeon, S.K.; Lee, J.Y. Effect of interconnection position of bicarbazole-triazine type bipolar host materials on the photophysical and device performances. J. Ind. Eng. Chem. 2017, 51, 295. [Google Scholar] [CrossRef]
  193. Chatterjee, T.; Hung, W.Y.; Tang, W.F.; Chen, H.F.; Wong, K.T. Carbazole-bridged triphenylamine-bipyridine bipolar hosts for high-efficiency low roll-off multi-color PhOLEDs. Org. Electron. 2017, 50, 204. [Google Scholar] [CrossRef]
  194. Braveenth, R.; Ahn, D.H.; Han, J.H.; Moon, J.S.; Kim, S.W.; Lee, H.; Qiong, W.; Kwon, J.H.; Chai, K.Y. Utilizing triazine/pyrimidine acceptor and carbazole-triphenylamine donor based bipolar novel host materials for highly luminescent green phosphorescent OLEDs with lower efficiency roll-off. Dye Pigment. 2018, 157, 377. [Google Scholar] [CrossRef]
  195. Tomkeviciene, A.; Puckyte, G.; Grazulevicius, J.V.; Kazlauskas, K.; Jursenas, S.; Jankauskas, V. Dimethyldiphenylamino-substituted carbazoles as electronically active molecular materials. Dye Pigment. 2013, 96, 574. [Google Scholar] [CrossRef]
  196. Jiang, W.; Duan, L.; Qiao, J.; Dong, G.; Zhang, D.; Wang, L.; Qiu, Y. High-triplet-energy tri-carbazole derivatives as host materials for efficient solution-processed blue phosphorescent devices. J. Mater. Chem. 2011, 21, 4918. [Google Scholar] [CrossRef]
  197. Zhang, X.; Yang, T.; Wei, Q.; Chen, Y.; Guo, X.; Xie, L.; Lai, W.; Fan, Q.; Qian, Y.; Huang, W. Arylfluorene based universal hosts for solution-processed RGB and white phosphorescent organic light-emitting devices. RSC Adv. 2015, 5, 94077. [Google Scholar] [CrossRef]
  198. Hung, W.Y.; Chi, L.C.; Chen, W.J.; Chen, Y.M.; Chou, S.H.; Wong, K.T. A new benzimidazole/carbazole hybrid bipolar material for highly efficient deep-blue electrofluorescence, yellow–green electrophosphorescence, and two-color-based white OLEDs. J. Mater. Chem. 2010, 20, 10113. [Google Scholar] [CrossRef]
  199. Chou, S.H.; Hung, W.Y.; Chen, C.M.; Liu, Q.Y.; Liu, Y.H.; Wong, K.T. Manipulation of connecting topology in carbazole/benzimidazole universal bipolar host materials for RGB and White PhOLEDs. RSC Adv. 2013, 3, 13891. [Google Scholar] [CrossRef]
  200. Seo, J.H.; Kim, H.M.; Choi, E.Y.; Choi, D.H.; Park, J.H.; Lee, K.H.; Yoon, S.S.; Kim, Y.K. Efficient Phosphorescent Green and Red Organic Light-Emitting Diodes Based on the Novel Carbazole-Type Host Material. J. Nanosci. Nanotechnol. 2011, 11, 1373. [Google Scholar] [CrossRef]
  201. Nagai, Y.; Sasabe, H.; Ohisa, S.; Kido, J. Effect of substituents in a series of carbazole-based host-materials toward high-efficiency carbene-based blue OLEDs. Mater. Chem. C 2016, 4, 9476. [Google Scholar] [CrossRef]
  202. Keruckas, J.; Grazulevicius, J.V.; Volyniuk, D.; Cherpak, V.; Stakhira, P. 3,6-Bis(indol-1-yl)-9-phenylcarbazoles as electroactive materials for electrophosphorescent diodes. Dye Pigment. 2014, 100, 66. [Google Scholar] [CrossRef]
  203. Park, M.S.; Lee, J.Y. 9-(Pyridin-3-yl)-9H-carbazole derivatives as host materials for green phosphorescent organic light-emitting diodes. Org. Electron. 2013, 14, 1291. [Google Scholar] [CrossRef]
  204. Wang, F.; Liu, D.; Li, J.; Ma, M. Modulation of n-Type Units in Bipolar Host Materials toward High-Performance Phosphorescent OLEDs. ACS Appl. Mater. Interfacce 2017, 9, 37888. [Google Scholar] [CrossRef] [PubMed]
  205. Kwak, J.; Lyu, Y.Y.; Lee, H.; Choi, B.; Char, K.; Lee, C. New carbazole-based host material for low-voltage and highly efficient red phosphorescent organic light-emitting diodes. J. Mater. Chem. 2012, 2, 6351. [Google Scholar] [CrossRef]
  206. Bin, J.K.; Cho, N.S.; Hong, J.I. New host material for high-performance blue phosphorescent organic electroluminescent devices. Adv. Mater. 2012, 24, 2911. [Google Scholar] [CrossRef]
  207. Li, H.; Bi, R.; Chen, T.; Yuan, K.; Chen, R.; Tao, Y.; Zhang, H.; Zheng, C.; Huang, W. Selectively Modulating Triplet Exciton Formation in Host Materials for Highly Efficient Blue Electrophosphorescence. ACS Appl. Mater. Interface 2016, 8, 7274. [Google Scholar] [CrossRef]
  208. Shi, H.; Xin, D.; Dong, X.; Dai, J.X.; Wu, X.; Miao, Y.; Fang, L.; Wang, H.; Choi, M.F.F. A star-shaped bipolar host material based on carbazole and dimesitylboron moieties for fabrication of highly efficient red, green and blue electrophosphorescent devices. J. Mater. Chem. C 2014, 2, 2160. [Google Scholar] [CrossRef]
  209. Ye, H.; Zhou, K.; Wu, H.; Chen, K.; Xie, G.; Hu, J.; Ma, S.; Su, S.J.; Cao, Y. Novel molecular host materials based on carbazole/PO hybrids with wide bandgap via unique linkages for solution-processed blue phosphorescent OLEDs. Opt. Mater. 2016, 60, 244. [Google Scholar] [CrossRef]
  210. Volyniuk, D.; Cherpak, V.; Stakhira, P.; Minaev, B.; Baryshnikov, G.; Tomkeviciene, A.; Keruckas, J.; Grazulevicius, J.V. Highly Efficient Blue Organic Light-Emitting Diodes Based on Intermolecular Triplet–Singlet Energy Transfer. J. Phys. Chem. C 2013, 117, 22538. [Google Scholar] [CrossRef]
  211. Xiang, C.; Fu, X.; Wei, W.; Liu, R.; Zhang, Y.; Balema, V.; Nelson, B.; So, F. Efficiency Roll-Off in Blue Emitting Phosphorescent Organic Light Emitting Diodes with Carbazole Host Materials. Adv. Funct. Mater. 2016, 26, 1463. [Google Scholar] [CrossRef]
Coatings 15 00398 g001
Figure 1. Structure of 9H-carbazole with numbering of atoms of the molcule.
Figure 1. Structure of 9H-carbazole with numbering of atoms of the molcule.
Coatings 15 00398 g001
Coatings 15 00398 sch001
Scheme 1. Chemical structures of the bipolar compounds A1–A31.
Scheme 1. Chemical structures of the bipolar compounds A1–A31.
Coatings 15 00398 sch001
Coatings 15 00398 sch002
Scheme 2. Chemical structures of 9-aryl-substituted carbazole-based compounds B1–B24.
Scheme 2. Chemical structures of 9-aryl-substituted carbazole-based compounds B1–B24.
Coatings 15 00398 sch002
Coatings 15 00398 sch003
Scheme 3. Chemical structures of 9-aryl-substituted carbazole-based compounds C1–C33.
Scheme 3. Chemical structures of 9-aryl-substituted carbazole-based compounds C1–C33.
Coatings 15 00398 sch003
Coatings 15 00398 sch004
Scheme 4. Structures of the bipolar twin compounds with two carbazole rings D1–D29.
Scheme 4. Structures of the bipolar twin compounds with two carbazole rings D1–D29.
Coatings 15 00398 sch004
Coatings 15 00398 sch005
Scheme 5. Structures of the bipolar twin derivatives with two carbazole rings E1–E34.
Scheme 5. Structures of the bipolar twin derivatives with two carbazole rings E1–E34.
Coatings 15 00398 sch005
Coatings 15 00398 sch006
Scheme 6. Structures of the bipolar derivatives with two carbazole rings F1–F20.
Scheme 6. Structures of the bipolar derivatives with two carbazole rings F1–F20.
Coatings 15 00398 sch006
Coatings 15 00398 sch007
Scheme 7. Structures of the twin derivatives G1–G15 with two carbazole rings.
Scheme 7. Structures of the twin derivatives G1–G15 with two carbazole rings.
Coatings 15 00398 sch007
Coatings 15 00398 sch008
Scheme 8. Structures of the twin derivatives H1–H12 with two carbazo-3-yl fragments.
Scheme 8. Structures of the twin derivatives H1–H12 with two carbazo-3-yl fragments.
Coatings 15 00398 sch008
Coatings 15 00398 sch009
Scheme 9. Structures 3(2)-aryl(arylamino)-substituted carbazoles I1–I4 as host materials (* is place of connection).
Scheme 9. Structures 3(2)-aryl(arylamino)-substituted carbazoles I1–I4 as host materials (* is place of connection).
Coatings 15 00398 sch009
Coatings 15 00398 sch010
Scheme 10. Structures of 3,6(2,7)-diaryl(arylamino)-substituted carbazoles J1–J27 as host materials.
Scheme 10. Structures of 3,6(2,7)-diaryl(arylamino)-substituted carbazoles J1–J27 as host materials.
Coatings 15 00398 sch010
Table 1. Properties of the host materials A1–A31 and efficiencies of PhOLEDs using the hosts.
Table 1. Properties of the host materials A1–A31 and efficiencies of PhOLEDs using the hosts.
HostTd [°C]/Tg [°C]HOMO/
LUMO/Et [eV]		Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
A1299/-6.14/2.57/-ITO/MoO3/TCTA/Ir(ppy)3:A1/TPBi/LiF/Al13.08/44.88/37.75
A2417/2315.61/2.56/2.64ITO/NPB/TCTA/A2: Ir(piq)2(acac)/TmPyPB/LiF/Al12.7/20.6/22.5
A3404/-5.66/3.22/2.34ITO/TAPC/A3: Ir(piq)2acac/Bebq2/LiF/Al13/7.7/7.6
A4401/905.69/3.20/2.44ITO/TAPC/A4: Ir(piq)2acac/Bebq2/LiF/Al16.4/9.6/9.4
A5390/-5.76/2.72/2.70ITO/MoO3/NPB/A5: Ir(ppy)2(acac)/BCP/Alq3/LiF/Al21.9/80.1/86.1
A6488/-6.10/3.13/2.85ITO/DNTPD/BPBPA/PCzAc/A6/DBFTrz/ZADN/LiF/Al.17.1/-/-
A7287/495.64/2.08/2.67ITO/HAT-CN/TAPC/A7: FIrpic/TmPyPB/Al.17.1/34.5/33.1
A8327/-5.71/2.13/2.74ITO/HAT-CN/TAPC/A8: FIrpic/TmPyPB/Al24.4/88.0/86.1
A9316/-5.62/2.19/2.87ITO/PEDOT:PSS/A9 4TCzBN/TPBi/Cs2CO3/Al11.53/21.91/-
A10383/875.62/2.10/3.03ITO/MoO3/NPB/TCTA/A10: FIrpic/TmPyPB/LiF/Al.24.1/57/45.9
A11271/905.89/2.19/2.64ITO/NPB/TCTA/A11: (tphpy)2Ir(acac)/Bphen//Liq/Al4.41/6.44/4.05
A12292/985.90/2.23/2.62ITO/NPB/TCTA/A12: (tphpy)2Ir(acac)/Bphen//Liq/Al5.08/17.9/11.6
A13287/845.85/2.26/2.89ITO/NPB/TCTA/A13: (tphpy)2Ir(acac)/Bphen//Liq/Al12.3/45/47.1
A14344/1115.56/2.42/2.82ITO/MoO3/TCTA/A14: Ir(ppy)2(acac)/BmPyPb/LiF/Al15.6/58.5/36.5
A15385/1195.56/2.35/2.84ITO/MoO3/TCTA/A15: Ir(ppy)2(acac)/BmPyPb/LiF/Al14.8/56.3/35.4
A16349/865.82/2.25/2.78ITO/MoO3/TAPC/TCTA/A16: FIrpic/TmPyPb/LiF/Al.26.2/54.5/52.2
A17299/635.86/2.3/2.94ITO/PEDOT:PSS/TAPC/mCP/A17: FIrpic/TmPyPb/LiF/Al16.3/31.9/22.3
A18382/975.78/2.24/2.95ITO/PEDOT:PSS/TAPC/mCP/A18: FIrpic/TmPyPb/LiF/Al18.9/37.9/26.5
A19383/1085.86/2.30/2.94ITO/PEDOT:PSS/TAPC/mCP/A19: FIrpic/TmPyPb/LiF/Al21.6/43.3/24.4
A20509/1845.95/2.56/2.55ITO/NPB/TCTA/A20: Ir(ppy)2(acac)/BPhen/LiF/Al7.07/26.21/26.72
A21358/865.69/2.12/3.57ITO/PEDOT:PSS/TCTA/A21: Os(bpftz)2(PPhMe2)2/TPBi/LiF/Al16.5/20.3/18.8
A22331/775.68/2.15/3.53ITO/PEDOT:PSS/TCTA/A22: (Bt)2Ir(acac)/TPBi/LiF/Al17.5/43/38
A23445/-6.06/2.80/3.14ITO/MoO3/m-MTDATA/MoO3/m-MTDATA/Ir (ppz)3/A23:
FIrpic/BPhen/LiF/Al		5.2/10.4/9.3
A24439/-6.04/2.82/3.62ITO/MoO3/m-MTDATA/MoO3/m-MTDATA/Ir (ppz)3/A24:
FIrpic/BPhen/LiF/Al		9.8/20.9/20.0
A25369/-5.99/2.22/3.09ITO/MoO3/m-MTDATA/MoO3/m-MTDATA/Ir (ppz)3/A25:
FIrpic/BPhen/LiF/Al		9/17.4/17.1
A26365/-6.04/2.88/2.61ITO/MoO3/m-MTDATA/MoO3/m-MTDATA/Ir (ppz)3/A26:
FIrpic/BPhen/LiF/Al		9.3/18.3/17.9
A27353./615.57/2.47/2.84ITO/PEDOT:PSS/TAPC/TCTA/A27: Ir(ppy)3/TmPyPB/LiF/Al 28/97.9/102.5
A28362/635.58/2.60/2.54ITO/PEDOT:PSS/TAPC/TCTA/A28: Ir(ppy)3/TmPyPB/LiF/Al23.6/79.7/100.2
A29301/585.61/2.26/2.95ITO/PEDOT:PSS/TAPC/TCTA/A29:Ir(ppy)3/TmPyPB/LiF/Al20.9/71.3/56.5
A30328/605.63/2.34/2.71ITO/PEDOT:PSS/TAPC/TCTA/A30:Ir(ppy)3/TmPyPB/LiF/Al23.3/80.3/72.0
A31336/-5.61/2.35/2.67ITO/PEDOT:PSS/TAPC/TCTA/A31:Ir(ppy)3/TmPyPB/LiF/Al27.3/91.8/65.0
Table 2. Properties of the hosts B1–B23 and efficiencies of PhOLEDs using the derivatives.
Table 2. Properties of the hosts B1–B23 and efficiencies of PhOLEDs using the derivatives.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [eV]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
B1-/1096.15/2.78/2.72ITO/PEDOT: PSS/TAPC/mCP/B1: Firpic/TSPO1/LiF/Al13.7/35.3/26.1
B2-/976.06/2.88/2.76ITO/PEDOT: PSS/TAPC/mCP/B2: Firpic/TSPO1/LiF/Al19.1/-/35.5
B3434/1275.31/2.08/2.59ITO/MoO3 TAPC/TCTA/B3: Ir(ppy)3/TmPyPB/LiF/Ag:Mg13.8/48.4/50.6
B4426/1275.65/2.42/3.06ITO/TAPC/B4: Ir(dbi)3)/BCP/LiF/Al-/41.6/43
B5352/1705.61/2.12/3.03ITO/MoO3/NPB/TCTA/B5: Fir6/Tm/TPBi/LiF/Al19.5/40/36
B6315/1015.68/2.18/3.02ITO/PEDOT:PSS/TAPC/mCP/B5:Ir(cb)3/TSPO1TPBi/LiF/Al17.1/18.3/26.3
B7409/1046/2.35/3.03ITO/HAT-CN/TAPC/4CzIPN: B7/TPBi/Liq/Al20.5/62.1/51.3
B8404/1076/2.35/3.03ITO/HAT-CN/TAPC/4CzIPN: B8/TPBi/Liq/Al21.7/68.7/59.5
B9441/725.71/2.17/2.71ITO/HAT-CN/TAPC/TCTA/B9: Ir(ppy)3/Liq/Al 15.83/55.84/54.55
B10425/1205.55/1.88/2.68ITO/MoO3/NPB/TCTA/B10: FIrpic/TPBi/LiF/Al9.3/22/19.8
B11358/975.41/1.78/2,72ITO/MoO3/NPB/TCTA/B11: Firpic/TPBi/LiF/Al11.4/29.3/19.8
B12513/1476.54/3.51/2.79ITO/BCFA/mCP/B12: CNIr/DBFTrz//LiF/Al13.7/-/-
B13484/1296.46/3.44/2.84ITO/BCFA/mCP/B13: CNIr/DBFTrz//LiF/Al20.9/-/-
B14418/1166.34/3.07/3.09ITO/BCFN:HATCN/BCFN/mCBP/mCBP:B14 DBFTrz/ZADN/LiF/Al21.8/24.8/23.4
B15366/965.88/2.33/3ITO/NPB/mCP/B14: Firpic/TmPyPb/LiF/Al31.8/73.5/64.4
B16403/1125.72/2.67/2.37ITO/PEDOT:PSS/NPB/TCTA/mCP/B15: Ir(piq)2(acac)/TPBi/LiF/Al12.2/21.9/15.4
B17390/1075.81/2.65/2.40ITO/PEDOT:PSS/NPB/TCTA/mCP/B16: Ir(piq)2(acac)/TPBi/LiF/Al9.2/15.7/11.9
B18357/1045.82/2.46/2.65ITO/PEDOT:PSS/NPB/TCTA/mCP/B17: Ir(piq)2(acac)/TPBi/LiF/Al13.4/21.2/13.4
B19475/-5.20/2.22/2.46ITO/HATCN/TAPC/TCTA/B19:PO-01/TPBi/TmPyPB/LiF/Al20.1/60.3/57.7
B20436/1325.72/2.35/2.71ITO/MoO3/NPB/TCTA/B18: Ir(ppy)3/TPBi/LiF/Al17.1/69.2/59.5
B21483/1235.72/2.42/2.7ITO/MoO3/NPB/TCTA/B19: Ir(ppy)3/TPBi/LiF/Al12.3/46.2/40.7
B22446/1175.72/2.44/2.72ITO/MoO3/NPB/TCTA/B20: Ir(ppy)3/TPBi/LiF/Al15.3/53.4/43
B23402/1285.67/2.18/2.81ITO/PEDOT:PSS/B21: OXD-7:FIrpic/TPBI/Cs2CO3/Al9.2/21.7/-
B24454/1605.40/2.30/2.6ITO/α-NPD/TCTA/mCP/B22: Ir(piq)2acac/TmPyPB/LiF/Al16.6/12.4/13.4 l
Table 3. Properties of the materials B1–B23 and efficiencies of PhOLEDs using the host derivatives.
Table 3. Properties of the materials B1–B23 and efficiencies of PhOLEDs using the host derivatives.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [eV]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
C1337/1406.16/2.76/2.95ITO/DNTPD/NPB/mCP/C1: FCNIrpic/TSPO1/LiF/Al13,3/-/-
C2417/73-/-/2.97ITO/TAPC/C2: FIrpic/ETL/LiF/Al11.4/39.9/41.8
C3430/1505.66/2.18/2.25ITO/NPB/HATCN/NPB/C3: Ir(phq)2(acac)/TpPyPB/LiF/Al 10.3/19.5/20.4
C4369/2235.69/2.57/2.96ITO/PEDOT:PSS/PVK/C4/TPBi/LiF/Al 18.8/64.1/40.3
C5401/1535.75/2.61/2.87ITO/HATCN/NPB/TCTA/mCP/C5/DPEPO/Bphen/LiF/Al14.8/-/29.5
C6-/-5.41/1.39/3ITO/DNTPD/NPB/mCP/C6: FCNIrpic/TSPO1/LiF/Al 20/26.4/22.6
C7367/895.55/2.89/2.5ITO/HATCN/TAPC/C7: Ir(MDQ2(acac) Liq/Al15.1/21.4/20
C8388/-5.57 3.00/2.36ITO/HATCN/TAPC/C8: Ir(MDQ2(acac) Liq/Al10.5/12/14.5
C9457/1376.13/2.64/2.67ITO/PEDOT:PSS/TAPC/mCP/C9:Ir(ppy)2(acac)/TSPO1/TPBi/LiF/Al18.9/-/48.7
C10418/1305.54/1.80/2.43ITO/PEDOT: PSS/TAPC/TCTA/Ir(pq)2acac: C10/TmPyPB/LiF/Al. Red PhOLEDs23/39.2/26.4
C11451/-5.52/1.86/2.47ITO/PEDOT: PSS/TAPC/TCTA/Ir(pq)2acac: C11/TmPyPB/LiF/Al. Red PhOLEDs22.1/38.6/38.4
C12458/1426.53/3.31/2.29ITO/DNTPD/NPB/C12: Ir(pq)2acac/BCP/Alq3/LiF/Al9.65/15.4/7.62
C13345/975.49/2.34/2.99ITO/MoO3/m-MTDATA: MoO3/m-MTDATA/Ir(ppy)3/C13:
FIrpic/Bphen/LiF/Al.		8.9/20/17.9
C14311/1275.52/1.97/2.80ITO/CuPc/NPB/TCTA/C14: Ir(ppy)3/TPBi/Al17.5/67.9/45.4
C15348/1505.74/2.20/2.84ITO/HAT-CN/TAPC/C15: FIrpic: PO-01/TmPyPB/Liq/Al.21.5/60.2/43.6
C16414/1165.40/1.93/2.80TO/HAT-CN/TAPC/C16: Ir(MDQ)2(acac)/TmPyPB/Liq/Al23.2/34/33.5
C17332/-5.87/2.48/2.54ITO/NPB/TcTa/C17: (tphpy)2Ir(acac)/Bphen/Liq/Al8.09/29.6/26.6
C18304/-5.97/2.80/2.59ITO/NPB/TcTa/C18: (tphpy)2Ir(acac)/Bphen/Liq/Al5.23/15.1/12.1
C19-/--/-/-ITO/MoO3/NPB/mCP/C19: FIrpic/TmPyPB/LiF/Al3.24/8.58/6.24
C20386/1205.70/2.46/2.94ITO/MoO3/NPB/mCP/C20: FIrpic/TmPyPB/LiF/Al19.7/47.7/29.1
C21368/1055.72/2.39/2.96ITO/MoO3/NPB/mCP/C21: FIrpic/TmPyPB/LiF/Al20.1/42.6/31.7
C22355/1015.73/2.45/2.78ITO/MoO3/NPB/mCP/C22: FIrpic/TmPyPB/LiF/Al16.5/34.9/23
C23-/-6.06/2.55/2.89deep blue PhOLED24.3/-/-
C24-/-6.06/2.62/2.96deep blue PhOLED21.9/-/-
C25-/-6.08/2.49/2.96deep blue PhOLED17/-/-
C26462/985.98/2.57/2.79ITO/MoO3/TAPC/C26: FIrpic/TmPyPB/Liq/Al16.6/36.5/25.6
C27488/1405.99/2.56/2.74ITO/MoO3/TAPC/C27: FIrpic/TmPyPB/Liq/Al13.9/33/25.9
C28350/3005.7/2.35/2.82ITO/PEDOT: PSS/PVK/C28: t4CzIPN/TPBi/LiF/Al24/82.2/46.9
C29314/935.7/2.62/-ITO/PEDOT: PSS/TSPO1/C29: Ir(ppy)2(acac)/TPBi/LiF/Al13.3/39.2/23.4
C30338/1035.78/2.54/-ITO/PEDOT: PSS/TSPO1/C30: Ir(ppy)2(acac)/TPBi/LiF/Al 19.6/67/34.5
C31321/1105.74/2.77/-ITO/PEDOT: PSS/TSPO1/C31: Ir(ppy)2(acac)/TPBi/LiF/Al17.3/53.6/25.2
C32512/1785.67/2.39/2.94ITO/MoO3/TAPC/TCTA/C32: Ir(ppy)3/TmPyPB/LiF/Al7.5/25.7/24.48
C33-/-5.75/2.09/2.8ITO/PEDOT: PSS/TAPC/mCP/C33: Ir(dbi)3/TSPO1/TPBI/LiF/Al26.2/
Table 4. Properties of the hosts D1–D29 and efficiencies of PhOLEDs using the host derivatives.
Table 4. Properties of the hosts D1–D29 and efficiencies of PhOLEDs using the host derivatives.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [Ev]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
D1412/1275.38/2.23/2.78ITO/MoO3/mCP/DPEPO/D1: FIrpic/DPEPO/TPBi/LiF/Al14.0/30.1/32.2
D2366/2095.74/2.34/3.01ITO/PEDOT: PSS/TAPC/D2: FIrpic/TmPyPB/LiF/Al17.3/36.7/37.5
D3366/806.33/2.45/3.03ITO/PEDOT: PSS/TAPC/D3: FIrpic/TmPyPB/LiF/Al15.8/28.6/15.3
D4-/-6.13/2.56/2.99ITO/DNTPD/NPB/mCP/D4: FCNirpic/TSPO/LiF/Al22.4/27.1/-
D5412/1165.86/1.74/-ITO/MoO3/NPB/mCP/D5: FIr6/DPDPOTZ/LiF/Al22.9/36.6/41.8
D6460/1265.67/2.55/2.76ITO/MoO3/TAPC/TCTA/D6: (Ir(pq)2acac/TmPyPB/LiF/Al,26.84/41.14/47.87
D7-/-5.8/3.4/2.71ITO/PEDOT: PSS/TAPC/D7: Ir(ppy)3/TSPO1/LiF/Al25.9/-/-
D8421/6.14/3.51/-ITO/PEDOT: PSS/TAPC/mCP/D8/TSPO1/TPBi/LiF/Al25.2/81.2/57.2
D9278/1506.04/2.83/3.06ITO/ReO3/CzSi/D9: 4CzIPN/PO-T2TLiq/Al24/74.4/81.3
D10281/-5.95/3.03/2.92ITO/ReO3/CzSi/D10: 4CzIPN/PO-T2TLiq/Al22.5/65/53.8
D11-/-6.08/2.38/2.99ITO/PEDOT: PSS/TAPC/C11: FIrpic/mCP/TSPO1/TPBi/LiF/Al11.1/20.8/7.2
D12342/1185.41/2.39/2.68ITO/TAPC/TCTA/D12: Ir(ppy)3/DPEPO/TmPyPB/LiF/Al19.3/69.1/88.1
D13335/875.71/2.17/2.74ITO/PEDOT: PSS/poly-TPD/D13 FIrpic/TSPO1/TPBi/LiF/Al5.2/9.6/-
D14358/1025.67/2.13/2.82ITO/PEDOT: PSS/poly-TPD/D14: FIrpic/TSPO1/TPBi/LiF/Al3.9/7.5/-
D15350/946.11/2.52/2.99ITO/PEDOT: PSS/TAPC/mCP/D15: FIrpic/TPBI/TSPO1/LiF/Al19.8/-/-
D16417/1305.51/1.57/2.93ITO/PEDOT: PSS/TAPC/TCTA/D16: FIrpic/TmPyPB/LiF/Al27.1/52.3/40.5
D17435/-5.71/2.01/2.92ITO/PEDOT: PSS/TAPC/TCTA/D17: FIrpic/TmPyPB/LiF/Al23.9/44.8/27.4
D18381/1175.8/2.3/3.1ITO/TAPC/mCP/D18: FIrpic/DPPS/LiF/Al27/57.5/48.9
D19378/1375.72/2.27/2.49ITO/TAPC/D19: Ir(ppy)3/TPBi/Liq/Al14.7/52.4/49
D20397/1405.76/2.43/2.46ITO/TAPC/D20: Ir(ppy)3/TPBi/Liq/Al24.6/88.5/78.5
D21301/1156.3/3.52/2.46ITO/PEDOT/TAPC/mCP/D21: PO-01/TSPO1/TPBi/LiF/Al24.6/79.3/49.6
D22320/-5.71/2.31/3.02ITO/PEDOT: PSS/TAPC/mCP/FIrpic:D22/LiF/Al16.3/33.0/32.1
D23331/-5.82/2.64/2.98ITO/PEDOT: PSS/TAPC/mCP/FIrpic:D23/LiF/Al11.3/23.7/17.3
D24328/-5.73/2.86/2.66ITO/PEDOT: PSS/TAPC/mCP/FIrpic:D24/LiF/Al6.5/14.6/11.7
D25395/-6.05/2.74/2.62ITO/MoO3/D25: Ir(ppy)2(acac)/Cs2CO3/Al21.5/74.9/56.3
D26403/-6.05/2.88/2.61ITO/MoO3/D26: Ir(ppy)2(acac)//Cs2CO3/Al26.8/92.2/106.1
D27360/-5.53/1.63/2.91ITO/PEDOT: PSS/TAPC/D27: FIrpic/DPEPO/TmPyPB/LiF/Al32.0/66.4/57.9
D28333/-5.50/1.36/3.05ITO/PEDOT: PSS/TAPC/D28: FIrpic/DPEPO/TmPyPB/LiF/Al22.3/48.9/47.9
D29-/-5.38/1.09/3.02ITO/PEDOT: PSS/TAPC/mCP/D29: Ir(dbi)2/TSPO1/TPBi/LiF/Al 22.81/-/31.37
Table 5. Properties of hosts E1–E34 and efficiencies of PhOLEDs using the host materials.
Table 5. Properties of hosts E1–E34 and efficiencies of PhOLEDs using the host materials.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [eV]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
E1480/2606.3/3/3ITO/NPB/TCTA/E1: Firpic:Ir(piq)2acac/TmPyPB/LiF/Al11.3/16.8/15.1
E2377/1105.71/2.30/3.12ITO/PEDOT: PSS/PVK/E2: OXD-7/Firpic/Ca/Al6.9/15.2/3.8
E3-/1455.67/2.15/2.85ITO/HATCN/TAPC/DCDPA/TCzTrz: E3/TSPO1/TPBi/LiF/Al18.7/32.7/
E4526/1536.40/3.32/2.98ITO/BPBPA:HATCN/BPBPA/mCBP/E4:Ir(cb)3/DBFTrz/ZADN/LiF/Al20.7/-/-
E5575/2525.75/2.32/2.98ITO/PEDOT: PSS/PVK/E5: t4CzIPN/TPBi/LiF/Al19.1/65.45/41.13
E6485/1595.56/2.21/3.04ITO/PEDOT:PSS/E6: Firpic/TmPyPb/TPBi/CsF/Al10.4/20.17/7.37
E7-/1375.76/2.19/2.56ITO/NPB/mCP/E7: Firpic/TAZ/LiF/Al23.5/45.1/40.6
E8467/1535.41/1.81/2.93ITO/TAPC/mPC/E8: 4CzIPN/DPPS/LiF/Al23.38/67.74/60.94
E9492/1505.58/2.23/2.81ITO/NPB/TCTA/E9: Ir(ppy)3/TPBi/LiF/Al 21.95/74.01/67.92
E10486/1505.65/1.82/2.95ITO/NPB/TCTA/E10: Ir(ppy)3/TPBi/LiF/Al 22.28/76.86/89.15
E11350/945.74/2.16/3.01ITO/PEDOT:PSS/TAPC/TCTA/E11: Firpic/TmPyPB/LiF/Al19.08/40.93/21.42
E12390/1215.62/2.14/2.81ITO/PEDOT:PSS/TAPC/TCTA/E12: Firpic/TmPyPB/LiF/Al23.14/46.81/24.50
E13440/1405.59/2.16/2.77ITO/PEDOT:PSS/TAPC/TCTA/E13:Firpic/TmPyPB/LiF/Al7.03/18.52/13.40
E14455/1026.05/2.65/2.71ITO/TPDPES:TBPAH/3DTAPBP/E14: Firpic/TmPyPBP/LiF/Al19.1/-/34.6
E15461/1076.15/2.77/2.78ITO/TPDPES:TBPAH/3DTAPBP/E15: Firpic/TmPyPBP/LiF/Al24.3/-/46.1
E16-/1676.14/3.17/2.71ITO/PEDOT:PSS/TAPC/PczAc/Mcp/E16:Ir(ppy)3/TSPO1/TPBi/LiF/Al15.5/-/-
E17415/-5.63/2.57/2.86ITO/PEDOT:PSS/TAPC/TCTA/E17:Ir(ppy)3/TmPyPB/LiF/Al17.5/60.4/44
E18418/1225.88/2.5/2.68ITO/NPB/TCTA/E18: Ir(ppy)3/TmPyPB/LiF/Al18.9/63.4/56.7
E19375/1695.90 2.52/2.54ITO/NPB/TCTA/E19: Ir(ppy)3/TmPyPB/LiF/Al17.5/59.8/55.7
E20437/1286.01/2.88/2.4ITO/PEDOT:PSS/TAPC/mCP)/E20: PO-01/TSPO1/TPBi/LiF/Al22.3/68.3/47.5
E21440/1196.08/2.54/2.5ITO/PEDOT:PSS/TAPC/mCP)/E21: PO-01/TSPO1/TPBi/LiF/Al19.7/47.5/-
E22453/-5.61/2.32/2.58ITO/NPB/E22: Ip(ppy)3/TPBI/LiF/Al -/11.7/11.1
E23454/1565.62/2.19/2.56ITO/NPB/E23: Ip(ppy)3/TPBI/LiF/Al-/13/11.2
E24478/1445.28/1.66/2.60ITO/PEDOT:PSS/TAPC/TCTA/E24: Ir(ppy)3/TmPyPB/LiF/Al22.4/77/43.2
E25502/1415.20/1.38/2.60ITO/PEDOT:PSS/TAPC/TCTA/E25: Ir(ppy)3/TmPyPB/LiF/Al25.6/90.3/69.6
E26544/635.59/2.35/2.43ITO/MoO3/NPB/E26: Ir(ppy)3/TPBI/LiF/Al12.7/39.7/40.8
E27-/1105.98/2.72/2.71ITO/HAT-CN/TAPC/E27: FIrpic/TmPyPB/Liq/Al5.6/13/10,7
E28-/1005.99/2.47/2.81ITO/HAT-CN/TAPC/E28: FIrpic/TmPyPB/Liq/Al6.8/16/16.8
E29464/1335.79/2.28/2.60ITO/MoO3/NPB/E29: Ir(ppy)3/BCP/Alq3/LiF/Al-/21.2/17.0
E30443/1125.80/2.32/2.72ITO/MoO3/NPB/E30: Ir(ppy)3/BCP/Alq3/LiF/Al-/45.9/46.8
E31450/1085.79/2.31/2.64ITO/MoO3/NPB/E31: Ir(ppy)3/BCP/Alq3/LiF/Al-/31.3 20.8
E32401/1285.50/2.02/2.92ITO/MoO3/NPB/TCTA/E32: Ir(MDQ)2(acac)/TPBI/LiF/Al12.8/17.2/12.8
E33415/-5.55/2.02/2.91ITO/MoO3/NPB/TCTA/E33: Ir(MDQ)2(acac) TPBI/LiF/Al12.7/20.1/13.1
E34423/135-/-/2.54ITO/HAT-CN/NPB/TCTA/mCBP/E34: AcDbp/nBPhen/Liq/Al13.7/14.9/10.2
Table 6. Characteristics of the derivatives F1–F20 and efficiencies of PhOLEDs using the host materials.
Table 6. Characteristics of the derivatives F1–F20 and efficiencies of PhOLEDs using the host materials.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [Ev]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
F1402/1325.92/2.68/2.56ITO/AQ1200/NPB/TCTA/F1: Ir(ppy)2(acac)/Bphen/LiF/Al12.1/44/13.1
F2395/1395.97/2.79/2.60ITO/AQ1200/NPB/TCTA/F2: Ir(ppy)2(acac)/Bphen/LiF/Al9.8/35.5/12.3
F3427/1395.99/2.84/2.62ITO/AQ1200/NPB/TCTA/F3: Ir(ppy)2(acac)/Bphen/LiF/Al14.3/48.5/20.6
F4-/-6.01/2.55/3.02ITO/HAT-CN/TAPC/F4: DPAC-TRZ/TSPO1/TPBi/LiF/Al20.8/-/
F5-/-6.07/2.62/3.04ITO/HAT-CN/TAPC/F5: DPAC-TRZ/TSPO1/TPBi/LiF/Al20.4/-/-
F6487/1486.12/2.98/2.88ITO/PEDOT: PSS/TAPC/Mcp/F6: Ir(ppy)3/TSPO1/LiF/Al21.1/67.7/39.7
F7451/1445.60/2.11/2.92ITO/TAPC/F7:Firpic/TmPyPB/LiF/Al 22.6/40.5/32.6
F8418/1285.73/2.21/2.92ITO/TAPC/F8:Firpic/TmPyPB/LiF/Al23.7/44.8/31.3
F9578/-5.61/2.11/2.92ITO/TAPC/F9:Firpic/TmPyPB/LiF/Al19.2/39.1/27.2
F10585/-5.60/2.09/2.93ITO/TAPC/F10:Firpic/TmPyPB/LiF/Al25.8/53.1/41.1
F11412/1386.06/2.68/2.97ITO/HATCN/TAPC/DCDPA/F11: DMAC-DPS/TSPO1/TPBi/LiF/Al18.8/31.2/-
F12-/-5.71/2.19/2.94ITO/HATCN/TAPC/2CzIPN: F12/TmPyPB/LiF/Al18.5/31.89/-
F13380/1336.06/2.68/2.75ITO/PEDOT: PSS/F13: Firpic/TmPyPB/CsF/Al 13.9/29.0/18.6
F14385/1255.24/1.72/3.03ITO/HATCN/NPB/TAPC/F14: Firpic/TmPyPB/LiF/Al13.4/23.1/21.0
F15420/1675.32/1.81/3.02ITO/HATCN/NPB/TAPC/F15: Firpic/TmPyPB/LiF/Al29/50.1/47.1
F16457/133 6.05/2.66/2.96ITO/PEDOT:PSS/F16: mSiTrz/Al 23/-/27.9
F17467/126 6.09/2.55/2.98ITO/PEDOT:PSS/F17: mSiTrz/Al22.4/-/26.3
F18419/1816.02/2.79/2.75ITO/TAPC/mCP/F18: Ir(ppy)3/TSPO1/LiF/Al20.6/71.1/43.4
F19370/1705.62/1.81/2.56ITO/MoO3/TAPC/F19: Ir(ppy)3/TmPyPb/LiF/Al -/21/11.9
F20480/-5.32/1.82/2.88ITO/HATCN/NPD/PtN3N-ptb:F20/BAlq/BPyTP/LiF/Al9.5/-/-
Table 7. Properties of the hosts G1–G15 and efficiencies of PhOLEDs using the materials.
Table 7. Properties of the hosts G1–G15 and efficiencies of PhOLEDs using the materials.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [Ev]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
G1424/1215.22/2.91/2.89ITO/MoO3/NPB/G1: DACT-II/TSPO1/TmPyPb/LiF/Al12.2/41.6/15.1
G2420/1235.29/2.97/3.01ITO/HAT-CN/NPB/G2: Ir(ppy)3/TSPO1/TPBi/LiF/Al12.6/44.1/36.8
G3379/795.4/2.4/2.86ITO/TAPC/mCP/G3: Firpic/DPPS/LiF/Al15.3/33.8/-
G4354/1455.8/2.2/2.97ITO/TAPC/mCP/G4: Firpic/DPPS/LiF/Al22/51.3/-
G5342/595.54/2.01/2.9ITO/PEDOT:PSS/G5: FIrpic/TmPyPB/LiF/Al-/13.8/7
G6344/1075.49/2.07/2.71ITO/PEDOT:PSS/G6: FIrpic/TmPyPB/LiF/Al-/2.9/1
G7366/1475.47/2.03/2.84ITO/PEDOT:PSS/G7: FIrpic/TmPyPB/LiF/Al-/8/2.3
G8-/-5.8/2.3/3.08ITO/PEDOT:PSS/TAPC/Mcp/G8: DBFTrz/TSPO1/TPBI/LiF/Al 16.4/25.2/-
G9300/1495.4/1.98/2.64ITO/MoO3/TAPC/TCTA/G9: 2CzPN/DPEPO/TmPyPB/LiF/Al11.7/28.9/23.3
G10375/1475.2/1.8//2.97ITO/MoO3/TCTA/mCP/G10: FIrpic/TSPO1/TPBi/LiF/Al3.6/-/-
G11383/1435.1/2/2.97ITO/MoO3/TCTA/mCP/G11: FIrpic/TSPO1/TPBi/LiF/Al4.2/-/-
G12495/3045.25/1.96/2.61ITO/PEDOT:PSS/G12:Ir(mppy)3/TPBi/Cs2CO3/Al 9.8/34.8/-
G13350/-5.71/2.08/3ITO/PEDOT: PSS/TAPC/mCP/G13: FIrpic/TmPyPB/LiF/Al7.6/13.7/4.7
G14450/-5.48/2.01/3ITO/PEDOT:PSS/NPB/TCTA/G14:FIrpic/TPBi/LiF/Al 7.5/18/8
G15-/2045.31/1.40/2.98ITO/PEDOT:PSS/G15: Ir(ppy)3/TPBi/Cs2CO3/Al2.26/7.6/3
Table 8. Properties of the hosts H1–H12 and efficiencies of PhOLEDs using the materials.
Table 8. Properties of the hosts H1–H12 and efficiencies of PhOLEDs using the materials.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [Ev]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
H1366/1095.90/2.40/3.03ITO/ReO3/H1: PO-T2T: 4CzIPN/PO-T2T/CN-T2T/Liq/Al21.1/56.4/59.1
H2331/855.72/2.27/3.04ITO/ReO3/H2: PO-T2T: 4CzIPN/PO-T2T/CN-T2T/Liq/Al17.6/56.6/68.5
H3464/1385.53/2.34/3.05ITO/PEDOT:PSS/H3: FIrpic/DPEPO/TmPyPBLiq/Al9.6/21/8.5
H4242/-4.93/0.66/3.04ITO/m-MTDATA/H4: FIrpic/DPEPO/Bphen/Ca:Al1.2/4.2/12.5
H5420/1275.64/2.33/2.71ITO/HAT-CN/NPB/TCTA/mCBP/DACT-II: H5/TPBi/LiF/Al19.5/-/41.1
H6403/1285.69/2.44/2.64ITO/HAT-CN/NPB/TCTA/mCBP/DACT-II: H6/TPBi/LiF/Al22.7/-/53.4
H7390/1336.06/2.53/3.0ITO/DNTPD/NPB/TAPC/H7: FIrpic/TSPO1/LiF/Al18.9/-/-
H8425/1025.58/2.11/2.62ITO/PEDOT:PSS/TAPC/TCTA/H8:Ir(ppy)3/TmPyPB/LiF/Al22.2/72.5/52.5
H9-/-5.6/2.2/2.8ITO/TcTa/H9: FIrpic/TmPyPB/LiF/Al-/21.0/12.0
H10371/1205.46/2.16/2.66ITO/MoO3/NPB/TCTA/H10: Ir(ppy)2(acac)/TPBi/LiF/Al-/44.7/42.8
H11442/1455.48/2.22/2.54ITO/MoO3/NPB/TCTA/H11: Ir(ppy)2(acac)/TPBi/LiF/Al-/50.7/50.7
H12432/1095.40/2.12/2.65ITO/MoO3/TCTA/H12: Ir(piq)2acac/TPBi/LiF/Al14.1/9.7/8.9
Table 9. Properties of hosts I1–I32 and the efficiencies of PhOLEDs using the materials.
Table 9. Properties of hosts I1–I32 and the efficiencies of PhOLEDs using the materials.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [Ev]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
I1180/-5,58/2.34/3.47--
I2334/-5.44/1.89/3.39--
I3304/-5.45/1.99/3.02ITO/MoO3/NPB/TCTA/I3: Ir(ppy)3/TPBI/LiF/Al26/34.8/117
I4318/-5.46/1.84/3.40--
I5344/-5.37/1.86/3.41--
I6145/-5.38/2.03/3.43--
I7360/-5.4/2.0/2.51ITO/TAPC/I7: Ir(ppy)3/B3PYMPM/LiF/Al16.7/62.5/69.7
I8290/1056.21/2.86/2.88ITO/I7: Ir(ppy)3/LiF/Al6.5/-/-
I9378/895.61/2.21/2.78ITO/PEDOT:PSS/TAPC/I9: Firpic or Ir(ppy)3/TmPyPB/LiF/Al19.5/40.8/28.9 or 29/91.2/57.6
I10423/2085.24/1.16/3.02ITO/MoO3/TAPC/I10: FIrpic/TmPyPB/LiF/Al17.5/26.4/38.1
I11240/1565.34/0.92/3.01ITO/MoO3/TAPC/I11: FIrpic/TmPyPB/LiF/Al22.5/46.9/49.1
I12431/-5.29/1.02/3.01ITO/MoO3/TAPC/I12: FIrpic/TmPyPB/LiF/Al-
I13207.3/-5.22/1.35/2.77ITO/Tris-PCz: ReO3/Tris-PCz/I13: (bt)2Ir(acac)/3NT2T/LiF/Al5/5.5/6.16
I14320/1016.01/2.61/3.40ITO/MoO3/TCTA/(Ir(piq)2acac:I14/TPBi/LiF/Al.18.7/65.2/74.3
I15444/976.1/2.82/3.28ITO/MoO3/TCTA/(Ir(piq)2acac:I15/TPBi/LiF/Al.17.8/62.2/69.3
I16395/1035.6/2.4/2.7/2.63ITO/MoO3/NPB/mCP/I16: FIrpic/TmPyPB/LiF/Al17/33.5/30.3
I17438/1155.63/2.42/2.59ITO/MoO3/TCTA/I17: Ir(piq)2acac/TPBi/LiF/Al18.4/64.2/63.3
I18432/1165.73/2.44/2.52ITO/MoO3/TCTA/I18: Ir(piq)2acac/TPBi/LiF/Al16.9/59.5/59.6
I19384/956.09/2.87/2.70ITO/MoO3/NPB/TCTA/I19: Ir(ppy)3/TPBi/LiF/Al15/51.7/37.8
I20-/-6.10/2.86/2.6ITO/2-TNATA/NPB/I20: Ir(ppy)3/Alq3/LiF/Al-/37.5/46.7
I21-/-5.93/2.77/2.5ITO/2-TNATA/NPB/I21: Ir(ppy)3/Alq3/LiF/Al-/2.5/3.2
I22-/-6.1/2.57/2.8ITO/PEDOT:PSS/DNTPD/BPBPA/PCZAC/I22:5CzCN/DBFTrz/ZADN17.1/-/-
I23-/-6.07/2.57/2.78ITO/PEDOT:PSS/DNTPD/BPBPA/PCZAC/I23:5CzCN/DBFTrz/ZADN16/-/-
I24324/2456.56/3.07/2.66ITO/MoO3/TCTA/I24: Ir(ppy)3/TPBi/LiF/Al13.5/48.2/50.4
I25326/1965.45/2.01/2.51ITO/MoO3/TCTA/I25: Ir(ppy)3/TPBi/LiF/Al12.2/42.6/38.2
I26-/-6.06/3.24/-ITO/PEDOT:PSS/TAPC/mCP/I26:Ir(ppy)3/TSPO1/TPBi/LiF/Al18.8/-/-
I27-/-6.06/3.25/-ITO/PEDOT:PSS/TAPC/mCP/I27:Ir(ppy)3/TSPO1/TPBi/LiF/Al18.4/-/-
I28425/1105.47/2.38/2.60ITO/Tris-PCz:ReO3/Tris-PCz/I28: (ppy)2Ir(acac)/CN-T2T/Liq/Al14.9/53.5/76.5
I29324/-5.49/2.41/2.59ITO/Tris-PCz:ReO3/Tris-PCz/I29: (bt)2Ir(acac)/CN-T2T/Liq/Al22.4/57.3/72.5
I30420/1085.48/2.45/2.57ITO/Tris-PCz:ReO3/Tris-PCz/I30: (ppy)2Ir(acac)/CN-T2T/Liq/Al22/79.8/102.5
I31425/-5.59/2.70/2.44ITO/HATCN/TAPC/I31: Ir(ppy)3/TmPyPB/LiF/Al15.4/45.6/-
I32400/-5.63/2.57/2.63ITO/HATCN/TAPC/I32: Ir(ppy)3/TmPyPB/LiF/Al16.4/48.7/-
Table 10. Properties of the hosts J1–J27 and efficiencies of PhOLEDs with the host materials.
Table 10. Properties of the hosts J1–J27 and efficiencies of PhOLEDs with the host materials.
HostTd [°C]/Tg [°C]HOMO/LUMO/Et [Ev]Device StructureEQE [%]/CE [cdA−1]/PE [lmW−1]
J1373/994.83/1.94/2.56ITO/CuI/BIPC3/J1/TCz1/Ca/Al17/13.5/-
J2411/1004.81/1.75/2.66ITO/CuI/BIPC3/J2/TCz1/Ca/Al5/15/-
J3417/2105.30/1.78/-ITO/PEDOT:PSS/TAPC/J3: FIrpic/TmPyPB/LiF/Al-/124/-
J4433/2285.54/1.82/2.86ITO/PEDOT:PSS/J4: Ir(mppy)3/TmPyPb/LiF/Al7.8/26/-
J5366/1255.61/1.87/2.87ITO/PEDOT:PSS/J5: Ir(mppy)3/TmPyPb/LiF/Al6.3/21.4/-
J6459/2445.58/1.77/2.86ITO/PEDOT:PSS/J6: Ir(mppy)3/TmPyPb/LiF/Al7.2/23.8/-
J7480/1705.49/2.37/2.48ITO/PEDOT:PSS/DTAF/J7: (pbi)2Ir(acac)/TPBI/LiF/Al19.2/62/62
J8359/-5.52/2.02/2.63ITO/PEDOT:PSS/DTAF/J8: Os(bpftz)2(PPhMe2)2/DPPS/LiF/Al 19.4/18.4/19.3
J9427/1535.60/2.14/2.63ITO/PEDOT:PSS/DTAF/J9: (PBi)2Ir(acac)/DPPS/LiF/Al 21.4/72.9/64.1
J10428/-5.54/1.27/2.99ITO/TAPC/Ir(dbfmi):J10/B3PyPB/LiF/Al9.42/19.9/10.4
J11428/-5.74/1.26/2.99ITO/TAPC/Ir(dbfmi):J11/B3PyPB/LiF/Al12.21/15.91/9.89
J12440/1156.04/1.50/2.99ITO/TAPC/Ir(dbfmi):J12/B3PyPB/LiF/Al20.8/29.9/33.4
J13393/89-/-/-ITO/CuI/J13: Ir(Fppy)3/TCz1/Ca/Al-/12.2/-
J14441/77-/-/-ITO/CuI/J14: Ir(Fppy)3/TCz1/Ca/Al-/-/-
J15459/92-/-/-ITO/CuI/J15: Ir(Fppy)3/TCz1/Ca/Al-/-/-
J16446/1255.50/2.19/2.87ITO/PEDOT: PSS/TAPC/J16: FIrpic/TmPyPB/LiF/Al21.6/41.4/31.2
J17480/1335.51/2.59/2.94ITO/PEDOT: PSS/TAPC/J17: FIrpic/TmPyPB/LiF/Al25.8/45.6/44.2
J18471/1255.50/2.50/2.68ITO/PEDOT: PSS/TAPC/J18: FIrpic/TmPyPB/LiF/Al21.6/45/40.4
J19498/1565.61/2.55/2.96ITO/PEDOT: PSS/TAPC/J19: FIrpic/TmPyPB/LiF/Al23.5/54.4/42.5
J20480/1455.63/2.54/2.94ITO/PEDOT: PSS/TAPC/J20: FIrpic/TmPyPB/LiF/Al27/51.9/46.5
J21-/-5.52/2.57/2.92ITO/PEDOT: PSS/TAPC/J21: (Ir(ppy)3/BmPyPb/LiF/Al7.8/23.8/19.5
J22482/1485.68/3.35/5.21ITO/MoO3/NPD/J22:(piq)2Ir(acac)/BCP/Bebq2/LiF/Al19.3/16.4/13
J23346/1685.54/2.30/2.62ITO/HATCN/NPB/TAPC/J23: Firpic/TmPyPB/LiF/Al27.2/46.3/36.5
J24402/1685.11/1.04/2.94ITO/MoOx/NPB/TCTA/J24: FIrpic/TmPyPB/Cs2CO3/Al20.7/43.7/32.7
J25234/1105.55/1.90/2.83ITO/TAPC/J25: Ir(ppy)2(acac)/BPhen/BPhen/Cs2CO3/Ag-/38.6/-
J26384/1306.48/2.83/2.77ITO/PEDOT: PSS/PVK/J26: FIrpic/Ba/Al-/1.14/-
J27364/1016.39/2.80/2.76ITO/PEDOT: PSS/PVK/J27: FIrpic/Ba/Al-/4.16/-
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Krucaite, G.; Grigalevicius, S. Low Molar Mass Carbazole-Based Host Materials for Phosphorescent Organic Light-Emitting Diodes: A Review. Coatings 2025, 15, 398. https://doi.org/10.3390/coatings15040398

AMA Style

Krucaite G, Grigalevicius S. Low Molar Mass Carbazole-Based Host Materials for Phosphorescent Organic Light-Emitting Diodes: A Review. Coatings. 2025; 15(4):398. https://doi.org/10.3390/coatings15040398

Chicago/Turabian Style

Krucaite, Gintare, and Saulius Grigalevicius. 2025. "Low Molar Mass Carbazole-Based Host Materials for Phosphorescent Organic Light-Emitting Diodes: A Review" Coatings 15, no. 4: 398. https://doi.org/10.3390/coatings15040398

APA Style

Krucaite, G., & Grigalevicius, S. (2025). Low Molar Mass Carbazole-Based Host Materials for Phosphorescent Organic Light-Emitting Diodes: A Review. Coatings, 15(4), 398. https://doi.org/10.3390/coatings15040398

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop