Triphenylene-based discotic liquid crystal dimers, oligomers and polymers

Discotic liquid crystals are unique nanostructures with remarkable electronic and optoelectronic properties. Triphenylene derivatives play a major role in the research on discotic liquid crystals. Following recent reviews of the chemistry of triphenylene-based monomeric liquid crystals, this article now reviews the chemistry and physical properties of triphenylene-based discotic dimeric, oligomeric and polymeric liquid crystals.     

Orientation control and fixation of discotic liquid crystal

We established hybrid, horizontal, vertical, and vertical-twisted alignment of discotic liquid crystals on web-coating thin film. Newly developed materials are the photopolymerizable discotic liquid crystals, in order to fix desired novel alignment, the alignment promoters that deposit toward air surface during web coating, followed by drying of solvent, and then accomplish desired alignment of liquid crystals, the alignment layers that promote desired alignment of liquid crystals from the substrate side and the chiral agents, which have strong chiral powers in small amounts. Hybrid aligned discotic liquid crystal thin film has proven quite effective in expanding the viewing angle of thin film transistor liquid crystal displays.     

Star-like discotic liquid crystals

The game of molecular engineering of liquid crystalline systems via a combination of molecular architecture and functionalization of mesogens has opened interesting perspectives in the field of liquid crystals. Here we report on the synthesis and characterization of star-like heptameric triphenylenes. The discotic subunits in these molecules have been arranged in a hexagonal fashion around a central discotic core, thus leading to a new type of molecular arrangement for discotic liquid crystals. These oligomers do not crystallize and combine a well-defined structure with a discotic polymer-like processing.     

Liquid crystal parameters through image analysis

A technique which combines image analysis and polarising optical microscope (POM) is a useful tool for the physical investigation of discotic liquid crystals, such as hexabutoxytriphenylene and hexahexyloxytriphenylene. This investigation includes the phase transitions, optical properties and order parameter as a function of temperature. Textures of discotic liquid crystals are captured as a function of temperature using POM. These microscopic textures are analysed using MATLAB software to compute statistical parameters, Legendre moments, optical parameters and order parameters of discotic liquid crystal samples. Compared with other techniques in the literature, the proposed methodology is a reliable and very simple technique for the physical investigation of liquid crystals.     

Inclusion of gold nanoparticles into a discotic liquid crystalline matrix

The thermophysical properties of mixtures of hexanethiolate-capped gold nanoparticles and three types of discotic liquid crystals, investigated using polarizing optical microscopy, differential scanning calorimetry and DC conductivity, indicate inclusion of gold nanoparticles into a matrix of triphenylene-based discotic liquid crystals.     

Recent developments in the chemistry of triphenylene-based discotic liquid crystals

Triphenylene-based discotic liquid crystals, which have already been used commercially in phase compensation films to improve the viewing angle of liquid crystal display devices, also have application potential as one-dimensional charge carrier systems useful in electrical conduction, photoconduction, electroluminescence, photovoltaic solar cells, gas sensing, optical data storage and other devices. Over the past 25 years, more than 500 triphenylene derivatives have been synthesized to explore these possibilities. Cammidge and Bushby reviewed the chemistry and physical properties of about 100 triphenylene-based discotic liquid crystals prepared up to 1995. This review summarizes advances in the chemistry of triphenylene-based discotic liquid crystals since late 1995.     

Self-organization of disc-like molecules: chemical aspects

The hierarchical self-assembly of disc-shaped molecules leads to the formation of discotic liquid crystals. These materials are of fundamental importance not only as models for the study of energy and charge migration in self-organized systems but also as functional materials for device applications such as, one-dimensional conductors, photoconductors, light emitting diodes, photovoltaic solar cells, field-effect transistors and gas sensors. The negative birefringence films formed by polymerized nematic discotic liquid crystals have been commercialized as compensation foils to enlarge the viewing angle of commonly used twisted nematic liquid crystal displays. To date the number of discotic liquid crystals derived from more than 50 different cores comes to about 3000. This critical review describes, after an in-depth introduction, recent advances in basic design principles and synthetic approaches towards the preparation of most frequently encountered discotic liquid crystals.     

Recent developments in the chemistry of triphenylene-based discotic liquid crystals

Triphenylene-based discotic liquid crystals, which have already been used commercially in phase compensation films to improve the viewing angle of liquid crystal display devices, also have application potential as one-dimensional charge carrier systems useful in electrical conduction, photoconduction, electroluminescence, photovoltaic solar cells, gas sensing, optical data storage and other devices. Over the past 25 years, more than 500 triphenylene derivatives have been synthesized to explore these possibilities. Cammidge and Bushby reviewed the chemistry and physical properties of about 100 triphenylene-based discotic liquid crystals prepared up to 1995. This review summarizes advances in the chemistry of triphenylene-based discotic liquid crystals since late 1995.     

盘状液晶材料（1）聚集态结构及分子工程

介绍了盘状液晶材料的相分类和不同聚集态结构的特点，并对盘状液晶体系的分子工程和其它扩展性研究进展了综述。     

Experimental studies on the phase diagram and physical properties of mixture of calamitic and discotic nematic liquid crystals

Physical studies on mixture of calamitic and discotic nematic liquid crystals are meagre although they are potential for optimising physical properties. Here, we report experimental studies on the phase diagram and physical properties of mixtures of ambient temperature discotic and calamitic nematic liquid crystals. A substantial decrease in several physical properties such as birefringence, dielectric anisotropy and elastic constants are observed with increasing wt% of discotic compound. On the other hand a large increase in the rotational viscosity is observed. Based on the experimental results a simple model of mutual orientation of the rod-like and disc-like molecules is proposed.     

Discotic liquid crystals. A brief review

Progress in the field of discotic liquid crystals is summarized, with emphasis on experimental results rather than theoretical developments. Examples are given of discotic mesogens (including metallo-mesogens) and discotic polymers, and the structures of the mesophases identified to date are described.     

Alpha-helical-within-discotic columnar structures of a complex between poly(ethylene oxide)-block-poly(l-lysine) and a hexa-peri-hexabenzocoronene

Poly(ethylene oxide)-block-poly(l-lysine) (PEO-PLL) was complexed with an amphiphilic hexa-peri-hexabenzocoronene (HBC). This produced a thermotropic liquid crystalline material (PEO-PLL-HBC), which was investigated by FTIR spectroscopy and differential scanning calorimetry as well as by wide- and small-angle X-ray scattering. It was found that the poly(l-lysine) blocks form an alpha-helical secondary structure. Each helix is surrounded symmetrically by six discotic columns of HBC, which gives an alpha-helical-within-discotic column structural entity. The dense packing of these entities produces hexagonal sublattices (formed by the columns) in the frame of a two-dimensional hexagonal lattice (formed by the helices). An order-order transition from a columnar structure Col1 to Col2 was found at 54 degrees C. The unit cell constants are 5.75 nm (Col1) and 6.60 nm (Col2). The larger unit cell size of Col2 was explained by a higher intracolumnar order of the latter in which the packing distance of the disklike HBC cores is well-defined (0.353 nm). PEO-PLL-HBC combines essential features of liquid crystals with a basic structural element of proteins into a single material.     

Selective Synthesis Substituted Derivatives of Hexa-peri-hexabenzocoronenes

Polycyclic aromatic hydrocarbons have been intensively studied in recent years. [1,2] They consist of flat disctype cores surrounded by flexible chains, which enable them to self-assemble into columnar mesophases. The packing behavior of these discotic liquid crystals renders them well suited materials for the study of one-dimensional transport processes such as electrical conductivity and photoconductivity along the columnar axis. These compounds also have good fluorescent property. We would like to report the design and synthesis of mono- or multi-substituted hexa-peri-hexabenzocoronenes and study the fluorescent property and structure relationship.     

Structure and dynamics of liquid-crystalline polymers with different molecular architectures

The structure and dynamics of liquid-crystalline polymers with different molecular architectures as revealed by multidimensional NMR Is described. Specific examples discussed Include semiflexible, rigid-rod, calamitic, and discotic systems. Structural aspects addressed are the determination of high rank order parameters, the micro-order in frozen liquid crystals and the packing of flexible side chains. Local dynamics In the glassy state, conformational dynamics and collective phenomena such as the development of convective director structures are discussed. It is demonstrated that advanced NMR spectroscopy yields highly specific information not available from conventional scattering, microscopic and relaxation techniques.     

Preliminary Communications Functionalization of discotic liquid crystals by direct substitution into the discogen ring α-Nitration of triphenylene-based discogens

Abstract

It is demonstrated for the first time that discotic liquid crystals can be functionalized by direct substitution into the central ring (core) of the discogen. It is shown that hexahexyloxy-triphenylene (HAT6) can be easily nitrated to give the mono-α-nitrated product exclusively. This material, which has a discotic mesophase range between room temperature and 136°C, can be modified to give α-amino-, α-acetylamino- and α,α'-diazo-HAT6. These new materials all show enantiotropic mesophases, have permanent dipole moments and some of them are coloured. This generally applicable approach opens up a route to an enormous range of new discotic liquid crystals.     

Synthesis and characterization of naphthalene-substituted triphenylene discotic liquid crystals

A series of naphthalene-substituted triphenylene liquid crystals (LCs), viz. triphenylene-2,3,6,7,10,11-hexayl hexakis(6-alkenyloxy-2-naphthoate)s (HTPnN compounds) were synthesized and characterized. Alkenyloxy groups containing three to eleven carbon atoms were used as peripheral spacers in these liquid crystals. The discotic liquid crystals synthesized trap one to three water molecules depending on the length of their peripheral spacers. Differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction measurements confirm both nematic (N_d) and rectangular disordered columnar (Col_rd) phases for most of the synthesized discotic LCs. The clearing temperatures of these discotic LCs increase with increasing peripheral spacer length. A hybrid aligned HTP9N sample was investigated to evaluate its optical performance. Retardation values of this hybrid sample decrease with increasing wavelength and increase with increasing measuring angle.     

Playing with discs

The hierarchical self-assembly of disc-shaped molecules leads to the formation of discotic liquid crystals. These intriguing materials are of fundamental importance not only as models for the study of energy and charge migration in self-organised systems, but also as functional materials for various device applications. This has fostered numerous developments in this field. In this article, we have summarised the author's and the collaborators' research work on discotic liquid crystals.     

Liquid crystalline properties in a series of disc-like compounds with two long alkyloxy chains attached to the core

We report the synthesis and characterization of a novel series of anthraquinone-based discotic liquid crystals, viz. 1,5-dialkyloxy-2,3,6,7-tetrakis(benzyloxy)anthra-9,10-quinones. To our knowledge, these are the first examples of discotic liquid crystals wherein only two, long flexible aliphatic chains are attached to the core. The rest of the four positions are substituted with bulky benzyloxy groups. Most of the compounds synthesized in this series are found to be liquid crystalline. They exhibit the typical texture of a columnar mesophase. Further, these compounds can serve as useful precursors for obtaining various unsymmetrical derivatives of 9,10-anthraquinones.     

Liquid crystalline properties in a series of disc-like compounds with two long alkyloxy chains attached to the core

We report the synthesis and characterization of a novel series of anthraquinone-based discotic liquid crystals, viz. 1,5-dialkyloxy-2,3,6,7-tetrakis(benzyloxy)anthra-9,10-quinones. To our knowledge, these are the first examples of discotic liquid crystals wherein only two, long flexible aliphatic chains are attached to the core. The rest of the four positions are substituted with bulky benzyloxy groups. Most of the compounds synthesized in this series are found to be liquid crystalline. They exhibit the typical texture of a columnar mesophase. Further, these compounds can serve as useful precursors for obtaining various unsymmetrical derivatives of 9,10-anthraquinones.     

Self-assembled discotic nematic liquid crystals formed by simple hydrogen bonding between phenol and pyridine moieties

New discotic nematic liquid crystals have been prepared through intermolecular hydrogen bonding between the core of 1,3,5-trihydroxybenzene (phloroglucinol, PG) or 1,3,5-tris(4-hydroxyphenyl)benzene (THPB) and the peripheral molecules of stilbazole derivatives. The various nematic phases formed by new hydrogen bonding building blocks were investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The first discotic complexes of PG and trans-4-alkoxy-4′-stilbazoles exhibited nematic columnar (N_C) and hexagonal columnar phases depending on the length of alkyl chains, which were considered as the basic discotic structure. Several structural variations on the building blocks were attempted to examine their effects on the liquid crystalline properties of discotic complexes. The nematic lateral phase (N_L) with enhanced intercolumnar order was observed for the complexes of PG and trans-4-cyanoalkoxy-4′ stilbazoles due probably to the strong dipole interactions between cyano groups at the end of alkoxy chains. By introducing the nonlinear structure in three arms of supramolecular discotic mesogen, a discotic nematic phase (N_D) was observed for the complex of THPB and trans-4-octyloxy-4 -stilbazole. The single hydrogen bonding between phenol and pyridine moieties in this study provides a simple and effective method for preparing the rarely found discotic nematic liquid crystals.