Special Issue "Synthesis and Properties of Light-emitting Liquid Crystals"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Liquid Crystals".

Deadline for manuscript submissions: closed (1 April 2019)

Special Issue Editor

Guest Editor
Prof. Shigeyuki YAMADA

Kyoto Institute of Technology, Faculty of Molecular Chemistry and Engineering, Kyoto, Japan
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Special Issue Information

Dear Colleagues,

Light-emitting molecules are utilized in daily life, for example, in lighting and optoelectronic devices, as well as sensing materials. To date, most of the developed organic light-emitting molecules only show intense luminescence in dilute solutions. This feature is useful in applications such as fluorescent brightening agents, diagnostic fluorescent markers, and fluorescent indicators. In contrast, because of concentration quenching or aggregation-caused quenching effect, luminescence from organic luminophores is often quenched in the condensed phase, such as the solid state. Since the early 2000s, however, extensive efforts have been devoted to overcome this problem, and various solid-state organic light-emitting molecules that are suitable for use in optoelectronic devices, have been developed.

As one of the condensed phases, liquid-crystalline (LC) phases have attracted enormous attention because a mesophase exists between the crystalline and isotropic liquid phases, and the aggregated structures can be reversibly switched by external stimuli. Currently, applications utilising this switchable LC property are limited to LC display devices, which control the transmittance of the backlight by electric-field stimulation. Owing to the intriguing phase-switching properties of LCs, the discovery of novel liquid-crystalline functional molecules has attracted significant interest in various fields.
Light-emitting liquid crystals possessing both light-emitting and LC properties are promising functional molecules that can switch light-emitting properties by changing their molecular aggregated structures via phase transition, e.g., crystal ⇄ LC ⇄ liquid. This Special Issue, titled “Synthesis and Properties of Light-Emitting Liquid Crystals”, is intended to provide an innovative and broad perspective on light-emitting molecules with liquid-crystalline properties, particularly focusing on molecular design, synthesis, and the light-emitting, as well as liquid-crystalline, properties.

The potential topics include, but are not limited to:

  • molecular design of molecules with both light-emitting and liquid-crystalline properties;
  • development of efficient synthetic protocols for light-emitting liquid crystals;
  • characterisation of the structure, photophysical properties excited by photons or electronic-fields, and liquid-crystalline behavior;
  • photoluminescent or electroluminescent properties in liquid-crystalline phases; and
  • applications using light-emitting liquid crystals.

Dr. Shigeyuki YAMADA
Guest Editor

Manuscript Submission Information

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Keywords

  • light-emitting molecules
  • liquid crystal
  • photoluminescence
  • electroluminescence
  • phase transition
  • switching property
  • stimuli-responsive property

Published Papers (4 papers)

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Research

Open AccessArticle
Thermochemically Stable Liquid-Crystalline Gold(I) Complexes Showing Enhanced Room Temperature Phosphorescence
Crystals 2019, 9(5), 227; https://doi.org/10.3390/cryst9050227
Received: 29 March 2019 / Revised: 25 April 2019 / Accepted: 26 April 2019 / Published: 27 April 2019
PDF Full-text (2429 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Gold(I) complexes are some of the most attractive materials for generating aggregation-induced emission (AIE), enabling the realization of novel light-emitting applications such as chemo-sensors, bio-sensors, cell imaging, and organic light-emitting diodes (OLEDs). In this study, we propose a rational design of luminescent gold [...] Read more.
Gold(I) complexes are some of the most attractive materials for generating aggregation-induced emission (AIE), enabling the realization of novel light-emitting applications such as chemo-sensors, bio-sensors, cell imaging, and organic light-emitting diodes (OLEDs). In this study, we propose a rational design of luminescent gold complexes to achieve both high thermochemical stability and intense room temperature phosphorescence, which are desirable features in practical luminescent applications. Here, a series of gold(I) complexes with ligands of N-heterocyclic carbene (NHC) derivatives and/or acetylide were synthesized. Detailed characterization revealed that the incorporation of NHC ligands could increase the molecular thermochemical stability, as the decomposition temperature was increased to ~300 °C. We demonstrate that incorporation of both NHC and acetylide ligands enables us to generate gold(I) complexes exhibiting both high thermochemical stability and high room-temperature phosphorescence quantum yield (>40%) under ambient conditions. Furthermore, we modified the length of alkoxy chains at ligands, and succeeded in synthesizing a liquid crystalline gold(I) complex while maintaining the relatively high thermochemical stability and quantum yield. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-emitting Liquid Crystals)
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Figure 1

Open AccessArticle
2-Chloroalkoxy-Substituted Pentafluorinated Bistolanes as Novel Light-Emitting Liquid Crystals
Crystals 2019, 9(4), 195; https://doi.org/10.3390/cryst9040195
Received: 19 March 2019 / Revised: 2 April 2019 / Accepted: 3 April 2019 / Published: 6 April 2019
Cited by 1 | PDF Full-text (4684 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this study, we designed and synthesized novel pentafluorinated bistolane derivatives with 2-chloropentyl or 2-chlorohexyl flexible units as novel light-emitting liquid crystals (LELCs). By measuring the phase-transition behaviors, all derivatives were found to display liquid-crystalline (LC) phases during both heating and cooling processes. [...] Read more.
In this study, we designed and synthesized novel pentafluorinated bistolane derivatives with 2-chloropentyl or 2-chlorohexyl flexible units as novel light-emitting liquid crystals (LELCs). By measuring the phase-transition behaviors, all derivatives were found to display liquid-crystalline (LC) phases during both heating and cooling processes. Among the novel bistolanes, the S- and R-configured derivatives exhibited a chiral nematic (N*) phase with a typical Grandjean optical texture. Interestingly, the chiral derivatives also exhibited a blue phase with a typical platelet texture in a narrow temperature range (2–4 °C). Photophysical measurements revealed that the 2-chloroalkoxy-substituted pentafluorinated bistolanes exhibited intense photoluminescence (PL) both in solution and in crystalline phases. The PL characteristics, especially the maximum PL wavelength, were found to switch sensitively during the heating and cooling cycles depending on the molecular aggregates through the crystal (Cr) ⇄ N* phase transition. The 2-chloroalkoxy flexible units induced dynamic changes in the LC and PL properties, providing valuable insight into the potential of various LELCs as PL sensing materials. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-emitting Liquid Crystals)
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Graphical abstract

Open AccessArticle
A 1,6-Diphenylpyrene-Based, Photoluminescent Cyclophane Showing a Nematic Liquid-Crystalline Phase at Room Temperature
Crystals 2019, 9(2), 92; https://doi.org/10.3390/cryst9020092
Received: 21 January 2019 / Revised: 9 February 2019 / Accepted: 9 February 2019 / Published: 11 February 2019
PDF Full-text (2324 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Photoluminescent nematic liquid crystals have been an attractive research target for decades, because of their potential applications in optoelectrical devices. Integration of luminescent motifs into cyclic structures is a promising approach to induce low-ordered liquid-crystalline phases, even though relatively large and rigid luminophores [...] Read more.
Photoluminescent nematic liquid crystals have been an attractive research target for decades, because of their potential applications in optoelectrical devices. Integration of luminescent motifs into cyclic structures is a promising approach to induce low-ordered liquid-crystalline phases, even though relatively large and rigid luminophores are used as emitters. Here, we demonstrate a 1,6-diphenylpyrene-based, unsymmetric cyclophane showing a stable nematic phase at room temperature and exhibiting strong photoluminescence from the condensed state. The observed sky-blue photoluminescence was dominated by the emission species ascribed to assembled luminophores rather than monomers. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-emitting Liquid Crystals)
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Graphical abstract

Open AccessArticle
Synthesis of Furan-Substituted N-Heteroacene-Based Liquid Material and Its Acid-Recognizing Behavior
Crystals 2019, 9(1), 51; https://doi.org/10.3390/cryst9010051
Received: 25 December 2018 / Revised: 10 January 2019 / Accepted: 15 January 2019 / Published: 17 January 2019
Cited by 2 | PDF Full-text (2851 KB) | HTML Full-text | XML Full-text
Abstract
In this study, we synthesized a novel N-heteroacene-based liquid material 6,7-bis(3,7,11-trimethyl-1-dodecyloxy)-2,3-difurylquinoxaline (RPNL 1), containing two furan rings. We revealed that RPNL 1 adopted a disordered liquid at 25 °C, determined by polarized optical microscopic observation, differential scanning calorimetry, [...] Read more.
In this study, we synthesized a novel N-heteroacene-based liquid material 6,7-bis(3,7,11-trimethyl-1-dodecyloxy)-2,3-difurylquinoxaline (RPNL 1), containing two furan rings. We revealed that RPNL 1 adopted a disordered liquid at 25 °C, determined by polarized optical microscopic observation, differential scanning calorimetry, and X-ray diffraction measurements. The fluorescent spectrum measurement revealed that RPNL 1 showed a blue emission at 25 °C. Dissolving benzene sulfonic acid (BSA) in RPNL 1 brought about dramatic changes in its physical properties, such as emission colors, as well as sample states. Upon recognizing BSA, photoluminescent color was changed into orange, as well as phase transition occurred from liquid to a liquid-crystalline phase. RPNL 1 can function as an acid-recognizing material, accompanied with the color changes in emission. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-emitting Liquid Crystals)
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Graphical abstract

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