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Article

Side-Chain Labeling Strategy for Forming Self-Sorted Columnar Liquid Crystals from Binary Discotic Systems

by
Tsuneaki Sakurai
1,*,
Kenichi Kato
2 and
Masaki Shimizu
1
1
Faculty of Molecular Chemistry and Engineering, Kyoto Institute of Technology, Hashikami-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
2
RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun 679-5148, Japan
*
Author to whom correspondence should be addressed.
Crystals 2023, 13(10), 1473; https://doi.org/10.3390/cryst13101473
Submission received: 27 August 2023 / Revised: 6 October 2023 / Accepted: 7 October 2023 / Published: 10 October 2023
(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in Japan)
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Abstract

:
The spontaneous formation of self-sorted columnar structures of electron-donating and accepting π-conjugated molecules is attractive for photoconducting and photovoltaic properties. However, the simple mixing of donor–acceptor discotic molecules usually results in the formation of mixed-stacked or alternating-stacked columns. As a new strategy for overcoming this problem, here, we report the “side-chain labeling” approach using binary discotic systems and realize the preferential formation of such self-sorted columnar structures in a thermodynamically stable phase. The demonstrated key strategy involves the use of hydrophobic and hydrophilic side chains. The prepared blend is composed of liquid crystalline phthalocyanine with branched alkyl chains (H2Pc) and perylenediimide (PDI) carrying alkyl chains at one side and triethyleneglycol (TEG) chains at the other side (PDIC12/TEG). To avoid the thermodynamically unfavorable contact among hydrophobic and hydrophilic chains, PDIC12/TEG self-assembles to stack up on top of each other and H2Pc as well, forming a homo-stacked pair of columns (self-sort). Importantly, H2Pc and PDIC12/TEG in the blend are macroscopically miscible and uniform, and mesoscopically segregated. The columnar liquid crystalline microdomains of H2Pc and PDIC12/TEG are homeotropically aligned in a glass sandwiched cell. The “labeling” strategy demonstrated here is potentially applicable to any binary discotic system and enables the preferential formation of self-sorted columnar structures.

1. Introduction

The control of nanostructures and miscibility of binary blends is important for tuning the physical properties of the blended organic materials. Historically, polymer blend has been a famous notion, where the miscibility and compatibility of blended polymers have been well discussed, especially in view of their effect on thermal and mechanical properties [1,2,3,4]. The bulk heterojunction of conjugated polymers and fullerene derivatives is another famous concept utilized for blend films in organic photovoltaic cells [5,6,7]. More recently, blends of electron donors and acceptors based on conjugated polymers or small molecules have been used for active layers in organic electronic devices, including photovoltaic cells [8,9,10], electrochemical transistors [11], ambipolar transistors [12], and so on. In these blends, not only large interfaces of donor and acceptor molecules (or macromolecules) but also hole/electron-transporting bicontinuous interpenetrating networks are essential for the device operation. The optimization of such nanostructures in the blends is usually performed by a try-and-error approach using spin-coating methods. Meanwhile, hydrogen-bond-assisted organogelator systems have been demonstrated as a more elaborated molecular design [13,14,15,16]. In these systems, self-sorted fibrous one-dimensional assemblies were developed by the simple mixing of electron donor and acceptor molecules. The different distances of two hydrogen bonding sites between the donor and acceptor molecules are critical for the formation of self-sorting fibers. Although methodologies of bulk heterojunctions as well as binary organogelator systems have been established, they have a critical drawback: the obtained nanostructures are kinetically controlled but not thermodynamically stable in the long term. Thus, the construction of thermodynamic bicontinuous structures of electron donor and acceptor materials has been awaited.
Liquid crystal (LC) phases are usually thermodynamically stable and appropriate as a platform for constructing the arrays of π-conjugated systems through self-assembly, resulting in the functional soft materials [17,18,19,20,21,22,23]. However, there has been no example of binary LC blends with bicontinuous structures. In columnar LC phases of discotic π-systems, columnarly stacked π-conjugated molecules enable one-dimensional charge transport pathways. If electron-donating and accepting π-conjugated molecules form a self-sorted columnar structure, we can realize intracolumnar hole/electron transport pathways as well as intercolumnar p/n heterojunctions with large interfaces, which equips a long-term structural stability. However, in relevant previous studies, mixed-stacking columnar structures were reported from LC phthalocyanine (p-type: electron donor) and perylene diimide (PDI) (n-type: electron acceptor) molecules [24,25,26]. This is quite reasonable because they are entropically favored (Figure 1a). Special molecular designs are required to accomplish thermodynamically stable self-sorted columnar structures by the self-assembly of LC electron donor and acceptor molecules. Here, we report a “side-chain labeling” strategy to realize self-sorted columnar structures from LC mixtures composed of free-base phthalocyanine (H2Pc) and PDI derivatives PDIC12/C12, PDIC12/TEG, and PDITEG/TEG (Figure 2). The dissymmetric introduction of both hydrophobic and hydrophilic side chains in PDIC12/TEG gives large enthalpic gain to the homo-stacked PDI columns, and thus the self-sorted structure is stabilized when the PDIC12/TEG is mixed with H2Pc carrying hydrophobic chains (Figure 1b). Furthermore, the resulting self-sorted LC columns of the PDIC12/TEG and H2Pc molecules align homeotropically in a sandwiched glass cell, which is desirable for efficient charge transport in photovoltaic applications.
Entropically favored mixed-stacking structures can be formed because both electron donor and acceptor molecules are decorated with alkyl chains and they are molecularly miscible. We focused on strong enthalpic interactions of immiscible hydrophobic and hydrophilic chains. If donor (acceptor) molecules are substituted with alkyl chains and acceptor (donor) molecules with hydrophilic oxyethylene chains, they are not miscible but macroscopically segregated [27]. How do we access the thermodynamic self-sorted nanostructure? The clue is hidden in the amphiphilic molecular design used in previous works, including ours [28,29,30,31,32]. PDIC12/TEG (Figure 2) is a Janus-type amphiphilic compound forming a columnar LC phase at room temperature. PDIC12/TEG molecules pack into the rectangular columnar phase with p2mg symmetry to minimize the unfavorable contact among immiscible hydrophobic and hydrophilic side chains incorporated in a single PDI core. When H2Pc, a compound carrying hydrophobic chains, is blended with PDIC12/TEG, H2Pc molecules may not intercalate into a column of PDIC12/TEG to avoid the enthalpic penalty of increasing contacts between hydrophobic and hydrophilic segments. Nevertheless, they are macroscopically miscible with one another due to their hydrophobic chains. We expected that H2Pc molecules would form a homo-stacked columnar assembly and laterally contact with the hydrophobic chains of PDIC12/TEG, resulting in the self-sorted columnar assembly (Figure 1b). The preferential formation of a self-sorted nanostructure will be discussed in detail in the section of Results and Discussion.

2. Materials and Methods

2.1. Synthesis and Characterization of H2Pc and PDIs

H2Pc, PDIC12/C12, PDIC12/TEG, and PDITEG/TEG were synthesized according to the previous reports [31,33], and characterized by 1H NMR spectroscopy in CDCl3 on a Varian model Mercury 400 spectrometer, operating at 400 MHz, where chemical shifts were determined with respect to tetramethylsilane as an internal reference. MALDI-TOF mass spectrometry was performed on an Autoflex III spectrometer from Bruker, Japan, using dithranol as a matrix. In addition, 1:1 molar ratio mixtures of H2Pc and PDI derivatives were prepared from their CH2Cl2 solutions in a glass vial. The solvent was evaporated in each solution, allowing for as-prepared waxy LC mixture.

2.2. Characterization of LC Mesophases

The optical textures were recorded by a BX53-P polarizing optical microscope (POM) from Olympus, Japan, equipped with an EOS kiss X7i digital camera from Canon, Japan. The sample was loaded, by use of a capillary action, into an LC cell without any surface treatment. The LC cell was prepared as follows. The glasses with a size of 16 × 22 × 0.5 mm were purchased from Matsunami Glass Ind., Ltd. (Haemacytomer Cover Glasses), Osaka, Japan. Silica beads with 5 μm diameter were dispersed in a drop of fast curing optical adhesive (NOA81) purchased from THORLABS, and the beads-dispersed adhesive was spotted at four places in a rectangle on one glass. Another glass was placed onto the adhesive-spotted glass with a few millimeter offset along with the long axis. The sandwiched glass cell was irradiated with 365 nm light from a SLUV-4 handy UV lamp purchased from AS ONE, Japan, to complete the curing of the adhesive.
The temperature of the sample was controlled by a HS82 hot-stage from Mettler Toledo, Japan. Differential scanning calorimetry (DSC) measurements were performed on a DSC 822e differential scanning calorimeter from Mettler Toledo, Japan. Cooling and heating profiles were recorded and analyzed with the STARe system. Samples were put into an aluminum pan and allowed to be measured under N2 gas flow.
X-ray diffraction measurements were carried out using a synchrotron radiation X-ray beam with a wavelength of 0.108 nm on BL44B2 at the Super Photon Ring (SPring-8, Hyogo, Japan) [34]. A large Debye–Scherrer camera was used in conjunction with an imaging plate as a detector, and all diffraction patterns were recorded with a 0.01° step in 2θ. The samples were loaded by capillary action at the isotropic liquid melts into a 0.5 mm thick soda glass capillary purchased from WJM-Glas/Muller GmbH. During the measurements, samples were continuously rotated along the capillary axis to obtain a homogeneous diffraction pattern. The exposure time to the X-ray beam was 1.5 min each.

2.3. Evaluation of Intracolumnar Molecular Order

Electronic absorption spectra were recorded on a V-730 UV/VIS/NIR spectrophotometer from JASCO, Japan, where the scan rate, response, and band width were set at 1000 nm min−1, 0.06 s, and 1.0 nm. The CHCl3 solution samples were prepared at 2.0 × 10−5 M and measured in a quartz cell equipped with a screw cap. The optical path length of the cell is 1.0 cm. Spin-coated films were prepared from CHCl3 solutions of the single compound or 1:1 molar ratio H2Pc/PDI mixtures onto a quartz substrate with a size of 9 × 40 × 1 mm. The spin-coating was performed at 1500 rpm for 30 s using a Mikasa model MS B-100 spin coater.

3. Results and Discussion

3.1. Homeotropic Alignment Capability of H2Pc and PDIs

The phase transition behaviors of H2Pc, PDIC12/C12, PDIC12/TEG, and PDITEG/TEG were characterized by DSC (Figure S1). They all showed LC mesophases and their clearing points are 180, 223, 189, and 165 °C on cooling, respectively, which is almost identical with the previous reports [31,33]. A spontaneous homeotropic alignment of discotic columnar LCs was often reported for hexagonal columnar mesophases [35,36,37,38]. The homeotropic alignment capability of H2Pc discotic columns was already reported in a previous study [39]. The capability of spontaneous homeotropic alignment for the PDI derivatives was monitored by means of POM using samples.
After being loaded into the glass cell with a capillary action at the isotropic liquid phase (Iso), the sample was slowly cooled at 1.0 K/min. Then, the growth of dendritic textures was observed without a polarizer for all the PDI derivatives at around their clearing points (Figure 3a–c). At the same time, no optical texture appeared under crossed polarizers (Figure 3a–c). A similar behavior was seen for H2Pc with slow cooling at 1.0 K/min (Figure 3d), while defect areas with homogeneous alignment were confirmed upon rapid cooling at 10 K/min (Figure S2). These microscopic observations indicate the strong homeotropic tendency for the hexagonally arranged discotic columns from all four compounds (Figure 3e). Interestingly, after the phase transition from a hexagonal to rectangular columnar mesophase at around 110 °C upon cooling, the micrograph of PDIC12/TEG was almost unchanged, suggesting that the homeotropic orientation was kept upon the hexagonal–rectangular structural transformation.

3.2. Orientation, Phase Transition Behavior, and Phase Structure of H2Pc/PDI Mixtures

In order to confirm our hypothesis of the side-chain labeling strategy, 1:1 molar ratio mixtures of H2Pc/PDIC12/C12, H2Pc/PDIC12/TEG, and H2Pc/PDITEG/TEG were prepared and their phase behaviors were characterized. The three blend samples were loaded into a sandwich glass cell over 210 °C, and their optical textures were recorded upon cooling. Figure 4 shows optical micrographs with and without crossed polarizers and the dependence of the optical textures on the cooling rate. The mixture of H2Pc/PDITEG/TEG gave the most distinctive picture (Figure 4c,f). Independent of the cooling rate, the mixture clearly gave green and red color areas, which most likely correspond to the domains of H2Pc and PDITEG/TEG, respectively. The hydrophobic H2Pc and hydrophilic PDITEG/TEG are immiscible with each other and segregated macroscopically [27]. In contrast, H2Pc/PDIC12/C12 and H2Pc/PDIC12/TEG appear to have a homogeneous phase in the field of microscope view. Upon rapid cooling from their isotropic phases, fan-shaped textures appeared in POM upon Iso-to-LC phase transitions for both H2Pc/PDIC12/C12 and H2Pc/PDIC12/TEG (Figure 4a,b). The presence of textures indicates a non-homeotropic alignment of columnar structures. In contrast, the cooling rate was set at 1.0 K/min, and the growth of dendritic textures was seen in optical microscopy without polarizers, but almost dark field images were obtained under crossed polarizers (Figure 4d,e). Although the dark area ratio in these blends was a bit smaller than their constituent compounds, the homeotropic alignment capability was confirmed by POM observations.
The phase transition behaviors of the 1:1 molar ratio mixture of H2Pc/PDIC12/C12, H2Pc/PDIC12/TEG, and H2Pc/PDITEG/TEG were characterized by DSC. The DSC traces of H2Pc/PDIC12/C12 and H2Pc/PDIC12/TEG implied phase transitions from a mesoscopically uniform material (Figure 5). In the blend of H2Pc/PDIC12/C12, the clearing point (202 °C on cooling) is between H2Pc (180 °C) and PDIC12/C12 (223 °C) (Figure 5a and Figure S1), which is reasonable for molecularly miscible binary mixtures. In contrast, the clearing point of H2Pc/PDIC12/TEG (205 °C on heating) is higher than those of H2Pc (181 °C) and PDIC12/TEG (191 °C) (Figure 5b and Figure S1). This pattern is quite rare and interesting to note—the LC phase of the blend is thermodynamically more stable than the parent columnar phases. We will discuss this phenomenon in more depth with the powder X-ray diffraction (PXRD) patterns (vide infra). In the blend of H2Pc/PDITEG/TEG, the melting and clearing points of both the compounds are detected, though the clearing point at 192 °C is higher than that of H2Pc (181 °C) (Figure 5 and Figure S1). In other words, H2Pc/PDITEG/TEG affords the superimposed DSC chart of those of the constituent compounds. This is solely a sign of the macroscopic phase separation of H2Pc and PDITEG/TEG, which is consistent with the POM images.
Although the clearing points for H2Pc/PDIC12/C12 and H2Pc/PDIC12/TEG are almost identical, the values of phase transition enthalpy inform that the LC phase structure and degree of miscibility are completely different between these mixtures. The LC-to-Iso phase transition enthalpy changes (ΔH) were evaluated from the second heating trace in DSC (Figure S1) and are 4.8, 17.3, and 8.1 kJ mol−1 for H2Pc, PDIC12/C12, and PDIC12/TEG, respectively. The entropy changes upon these phase transitions (ΔS) can be estimated from the principle that Gibbs free energy is constant upon phase transition, i.e., ΔG = ΔH – TΔS = 0, where ΔG and T are Gibbs free energy change and absolute temperature. By substituting the evaluated ΔH and observed T into the above equation, the values of ΔS were estimated as 10.6, 34.8, and 17.4 J mol−1 K−1 for H2Pc, PDIC12/C12, and PDIC12/TEG, respectively. These values well explain the relatively larger entropic gain of linear dodecyloxy chains upon phase transition from columnar mesophase to isotropic liquid. The values of ΔH and ΔS are calculated for the 1:1 molar mixtures of H2Pc/PDIC12/C12 and H2Pc/PDIC12/TEG in a similar way, except that the average molecular weight of the two components is used for transforming the observed heat change into enthalpy values. The values of ΔS were estimated as 18.9 and 15.9 J mol−1 K−1 for H2Pc/PDIC12/C12 and H2Pc/PDIC12/TEG, respectively. The value of 18.9 J mol−1 K−1 for H2Pc/PDIC12/C12 is smaller than the averaged ΔS values calculated from those of the parent compound (22.7 J mol−1 K−1), implying that the molecules are disordered in the observed columnar mesophase. For example, one column is composed of H2Pc and PDIC12/C12 molecules. In contrast, the value of 15.9 J mol−1 K−1 for H2Pc/PDIC12/TEG is a bit larger than and even close to the averaged ΔS values of the parent compound (14.0 J mol−1 K−1). This similarity in the entropy values indicates the possibility that H2Pc and PDIC12/TEG form their respective microdomains. The molecular motion in the microdomains upon the phase transition would be consistent with that in the bulk of the corresponding compounds, while that at the interfaces of the microdomains is relatively limited. In this case, the ΔS value is expected to be smaller than the average values speculated from those for the parent compounds. Considering that the phase transition temperatures for these blends and parent compounds are close and in the range of 181–224 °C, the above speculations would have a certain level of significance. As below, we will directly discuss the molecular packing structures in the mesophase for LC blends based on the PXRD measurements.
The molecular packing structures in the mesophases were studied by means of PXRD measurements. In the mesophase at 80 °C, the 1:1 molar ratio mixture of H2Pc/PDIC12/C12 gave a diffraction pattern that is assignable to a hexagonal columnar phase with the lattice parameter of a = 32.1 Å (Figure 6a). Variable-temperature PXRD measurements elucidated that the hexagonal columnar mesophase was present at 30–200 °C (Figure S4). The parent hexagonal columnar mesophases of H2Pc and PDIC12/C12 have a lattice parameter of a = ~32 Å and ~31 Å, respectively (Figures S3 and S7). The size matching of these two molecules may be one of the critical reasons for stabilizing a uniform hexagonal packing of mixed-stacked columns. With the clearing temperature information discussed in the DSC section, we conclude that the H2Pc/PDIC12/C12 self-organized into molecularly miscible, entropically favored columns with hexagonal packing, as illustrated in Figure 7a. Interestingly, the mixture of H2Pc/PDIC12/TEG showed different behavior. Over 80 °C, the mixture formed a hexagonal columnar phase with a = ~32 Å (Figure S5). When being cooled down to 80 °C, the mixture changed its PXRD pattern to the superposition of those of H2Pc and PDIC12/TEG (Figure 6b), and similar superimposed patterns were also recorded at 50 and 30 °C (Figure S5). Namely, H2Pc and PDIC12/TEG are mesoscopically segregated but macroscopically miscible, as disclosed by PXRD and DSC measurements. The schematic illustration of H2Pc/PDIC12/TEG is shown in Figure 7b. Then, we tried to interpret the hexagonal columnar mesophase of H2Pc/PDIC12/TEG over 80 °C. Although a set of observed diffractions was assigned to a single hexagonal lattice, the (001) peak at d = ~3.4 Å, corresponding to the π-distance periodicity of PDIC12/TEG, obviously appeared as similar to those at 30–80 °C. In addition, as mentioned in the DSC analysis earlier, the clearing temperature of the mixture at 205 °C is higher than those of the parent compounds. Having these results in mind, we consider that H2Pc and PDIC12/TEG mainly form self-sorted columns even over 80 °C but the average domain size may be decreased. The blend H2Pc/PDITEG/TEG exhibited superimposed pattens of those of H2Pc and PDITEG/TEG below 240 °C (Figure 6 and Figure S6). These results are consistent with the macroscopic phase separation derived from the POM and DSC results. The illustration of macroscopically phase-separated columnar phases is shown in Figure 7c.

3.3. Intracolumnar Molecular Order in H2Pc/PDI Mixtures

The intracolumnar molecular order in the mesophases at room temperature was investigated by absorption spectroscopy of the thin film of the 1:1 molecular blends. In diluted CHCl3 solutions, both H2Pc and PDIC12/C12 are molecularly dispersed and show characteristic absorption at 600–750 nm and 400–550 nm, respectively, with strong vibronic coupling features (Figure 8a). In spin-coated LC films, these absorption bands become broad and blue-shifted due to the columnar assembly of molecules with π–π interactions (H-like aggregation). The spectra of PDIC12/TEG and PDITEG/TEG in the films are essentially the same as that of PDIC12/C12. Then, the spectra of the blend films were analyzed similarly. As expected, in the macroscopically phase-separated H2Pc/PDITEG/TEG blend film, the shape of the absorption spectra is almost the superposition of those of the parent LC films (Figure 8b and Figure S8). The heterotropic interactions hardly work due to the limited area of the interfaces between H2Pc and PDITEG/TEG. In the LC phase of H2Pc/PDIC12/C12, proposed as a molecularly miscible columnar phase, the absorption spectrum of the film is completely different from that of H2Pc/PDITEG/TEG. The characteristic two intense absorption bands from H2Pc and PDIC12/C12 both show vibronic structures in the blend film, while these bands are broadened compared to their solution states (Figure 8b). This feature strongly indicates that homotropic molecular interactions in their columnar assembly are broken, supporting the proposed molecularly miscible columnar phase (Figure 7a). The film of the H2Pc/PDIC12/TEG mixture afforded basically the superimposed spectrum of those of H2Pc and PDIC12/TEG. However, shoulder vibronic peaks at around 670–730 nm suggest that a small part of H2Pc columnar assemblies is dissociated by the intercalation of PDIC12/TEG. Thus, the picture of mesoscopically segregated self-sorted assembly as illustrated in Figure 7b may almost be correct, but the structural purity is less than perfect.

4. Conclusions

Although nanosegregated, bicontinuous structures of electron-donating and accepting π-conjugated molecules have been recognized as important for photoconducting and photovoltaic properties, only the kinetic control of such nanostructures has been reported so far. We conceived the side-chain labeling strategy using hydrophobic/hydrophilic chains to induce the homotropic self-assembly of donor and acceptor molecules and demonstrated the preferential formation of donor/acceptor self-sorted columnar structures in thermodynamically stable LC binary mixtures. In this LC blend, the columnar mesophases of H2Pc and PDI molecules are macroscopically miscible and uniform but mesoscopically segregated as evidenced by DSC and PXRD results. In addition, the intercalation of PDI (H2Pc) to the H2Pc (PDI) columns is minimally inhibited as supported by absorption spectroscopy. In a more comprehensive view, self-sorted nanostructures of binary mixtures are entropically unfavored in general, but the present work clarified that they can be accessed thermodynamically by self-assembly processes with the help of enthalpic interactions of immiscible side-chain pairs. Amphiphilic molecules—PDIC12/TEG in this work—induce mesoscopic phase separation and avoid macroscopic phase separation. This role is referred to as a compatibilizer in the research field of macromolecules [40]. While a small molecular compatibilizer has recently been reported [41], our work further extends the concept to the strategy of accessing self-sorted nanostructures. In future, the important subjects include the analysis and control of the size of donor and acceptor nano(micro)-domains, which will lead to the manipulation of photo and electronic functions originating from nanosegregated donor/acceptor blends.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst13101473/s1, Figure S1: DSC traces of H2Pc, PDIC12/C12, PDIC12/TEG, and PDITEG/TEG; Figure S2: Crossed polarized microscopy images of H2Pc in glass sandwich cell; Figure S3: Variable-temperature XRD patterns of H2Pc; Figure S4: Variable-temperature XRD patterns of 1:1 molar ratio mixture of H2Pc/PDIC12/C12; Figure S5: Variable-temperature XRD patterns of 1:1 molar ratio mixture of H2Pc/PDIC12/TEG; Figure S6: Variable-temperature XRD patterns of 1:1 molar ratio mixture of H2Pc/PDITEG/TEG; Figure S7: Schematic illustrations of columnar hexagonal and rectangular phases with corresponding lattice parameters and primary diffractions.

Author Contributions

T.S. conceived and designed the experiments; T.S. performed the experiments; T.S. and K.K. analyzed the data; T.S. and M.S. wrote the manuscript draft; K.K. revised the manuscript draft. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by JSPS KAKENHI numbers 20H02710 from the Japan Society for the Promotion of Science and a research grant from TEPCO Memorial Foundation.

Data Availability Statement

Not applicable.

Acknowledgments

The synchrotron radiation XRD experiments were performed at BL44B2 in SPring-8 with the approval of RIKEN. T.S. thanks the Leading Initiative for Excellent Young Researchers program by Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic illustrations of side-chain-directed molecular assembly of electron donors (orange) and acceptor (red) π-systems (a) substituted with hydrophobic side chains (green) alone and (b) site-specifically substituted with hydrophobic (green) and hydrophilic (blue) side chains.
Figure 1. Schematic illustrations of side-chain-directed molecular assembly of electron donors (orange) and acceptor (red) π-systems (a) substituted with hydrophobic side chains (green) alone and (b) site-specifically substituted with hydrophobic (green) and hydrophilic (blue) side chains.
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Figure 2. Chemical structures of liquid crystalline phthalocyanine H2Pc and perylenediimides PDIC12/C12, PDIC12/TEG, and PDITEG/TEG.
Figure 2. Chemical structures of liquid crystalline phthalocyanine H2Pc and perylenediimides PDIC12/C12, PDIC12/TEG, and PDITEG/TEG.
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Figure 3. Crossed polarized (left) and optical (right) microscopy images of (a) PDIC12/C12, (b) PDIC12/TEG, (c) PDITEG/TEG, and (d) H2Pc in glass sandwich cell without any treatment. (a–d) were taken at 222, 193, 168, and 181 °C, respectively, after cooling from their isotropic liquid phases at 1.0 K/min. Scale bars represent 200 µm. (e) Schematic illustration of LC samples in 5 µm thick sandwiched glass cell and homeotropic alignment of discotic columns formed in LC.
Figure 3. Crossed polarized (left) and optical (right) microscopy images of (a) PDIC12/C12, (b) PDIC12/TEG, (c) PDITEG/TEG, and (d) H2Pc in glass sandwich cell without any treatment. (a–d) were taken at 222, 193, 168, and 181 °C, respectively, after cooling from their isotropic liquid phases at 1.0 K/min. Scale bars represent 200 µm. (e) Schematic illustration of LC samples in 5 µm thick sandwiched glass cell and homeotropic alignment of discotic columns formed in LC.
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Figure 4. Crossed polarized (left) and optical (right) microscopy images of 1:1 molar ratio mixtures of (a,d) H2Pc/PDIC12/C12, (b,e) H2Pc/PDIC12/TEG, and (c,f) H2Pc/PDITEG/TEG in glass sandwich cell without any treatment. Images (a–c) were taken at 25 °C after rapid cooling from their isotropic melt. (d–f) were taken at 198, 200, and 161 °C, respectively, after cooling from their isotropic liquid phases at 1.0 K/min. Scale bars represent 200 µm.
Figure 4. Crossed polarized (left) and optical (right) microscopy images of 1:1 molar ratio mixtures of (a,d) H2Pc/PDIC12/C12, (b,e) H2Pc/PDIC12/TEG, and (c,f) H2Pc/PDITEG/TEG in glass sandwich cell without any treatment. Images (a–c) were taken at 25 °C after rapid cooling from their isotropic melt. (d–f) were taken at 198, 200, and 161 °C, respectively, after cooling from their isotropic liquid phases at 1.0 K/min. Scale bars represent 200 µm.
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Figure 5. DSC traces of 1:1 molar ratio mixtures of (a) H2Pc/PDIC12/C12, (b) H2Pc/PDIC12/TEG, and (c) H2Pc/PDITEG/TEG on 2nd heating/cooling cycle at 10 K/min.
Figure 5. DSC traces of 1:1 molar ratio mixtures of (a) H2Pc/PDIC12/C12, (b) H2Pc/PDIC12/TEG, and (c) H2Pc/PDITEG/TEG on 2nd heating/cooling cycle at 10 K/min.
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Figure 6. XRD patterns of 1:1 molar ratio mixtures of (a) H2Pc/PDIC12/C12 at 80 °C, (b) H2Pc/PDIC12/TEG at 80 °C, and (c) H2Pc/PDITEG/TEG at 160 °C. For comparison, the XRD patterns of the components for the blends are represented in (b,c).
Figure 6. XRD patterns of 1:1 molar ratio mixtures of (a) H2Pc/PDIC12/C12 at 80 °C, (b) H2Pc/PDIC12/TEG at 80 °C, and (c) H2Pc/PDITEG/TEG at 160 °C. For comparison, the XRD patterns of the components for the blends are represented in (b,c).
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Figure 7. Schematic illustrations of proposed molecular assembly in columnar LC phases for (a) H2Pc/PDIC12/C12, (b) H2Pc/PDIC12/TEG, and (c) H2Pc/PDITEG/TEG. Red and green disks represent corresponding H2Pc and PDI molecules.
Figure 7. Schematic illustrations of proposed molecular assembly in columnar LC phases for (a) H2Pc/PDIC12/C12, (b) H2Pc/PDIC12/TEG, and (c) H2Pc/PDITEG/TEG. Red and green disks represent corresponding H2Pc and PDI molecules.
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Figure 8. (a) Absorption spectra of H2Pc (green) and PDIC12/C12 (red) in spin-coated film (solid line) and in CHCl3 (dotted line). (b) Absorption spectra of spin-coated film of H2Pc/PDIC12/C12 (red), H2Pc/PDIC12/TEG (green), and H2Pc/PDITEG/TEG (blue).
Figure 8. (a) Absorption spectra of H2Pc (green) and PDIC12/C12 (red) in spin-coated film (solid line) and in CHCl3 (dotted line). (b) Absorption spectra of spin-coated film of H2Pc/PDIC12/C12 (red), H2Pc/PDIC12/TEG (green), and H2Pc/PDITEG/TEG (blue).
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Sakurai, T.; Kato, K.; Shimizu, M. Side-Chain Labeling Strategy for Forming Self-Sorted Columnar Liquid Crystals from Binary Discotic Systems. Crystals 2023, 13, 1473. https://doi.org/10.3390/cryst13101473

AMA Style

Sakurai T, Kato K, Shimizu M. Side-Chain Labeling Strategy for Forming Self-Sorted Columnar Liquid Crystals from Binary Discotic Systems. Crystals. 2023; 13(10):1473. https://doi.org/10.3390/cryst13101473

Chicago/Turabian Style

Sakurai, Tsuneaki, Kenichi Kato, and Masaki Shimizu. 2023. "Side-Chain Labeling Strategy for Forming Self-Sorted Columnar Liquid Crystals from Binary Discotic Systems" Crystals 13, no. 10: 1473. https://doi.org/10.3390/cryst13101473

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