The first examples of discotic liquid crystalline gemini surfactants

Six novel gemini imidazolium salts tethered with hexaalkoxytriphenylene moieties were prepared by quaternization of imidazole nitrogen with ω-bromo-substituted triphenylene derivatives. Their chemical structures were examined by ¹H NMR, IR, UV, MS, and elemental analyses. The mesomorphic properties of these discotic dimeric salts were investigated by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction studies. These triphenylene-imidazole-based gemini dimers with bromide as counter ion were found to exhibit liquid crystalline behavior over a wide temperature range and display ionic conductivity in the range of 10⁻⁶ to 10⁻⁵ S/m. These materials tend to form monolayer at the air-water interface.     

Vanadium oxytrichloride,a novel reagent for the oxidative trimerization of o-dialkoxybenzenes to hexaalkoxytriphenylenes

Triphenylene derivatives with six peripheral chains can make excellent discotic liquid crystals showing great promise in electronic devices. Vanadium oxytrichloride was found to be a novel reagent for the preparation of various triphenylene derivatives. Symmetrically substituted hexaalkoxytriphenylenes were obtained from o-dialkoxybenzenes by oxidative trimerization with VOCl₃ in high yields. Oxidative coupling of a 3,3',4,4'-tetraalkoxybiphenyl with 1,2-dialkoxybenzenes yielded unsymmetrically substituted derivatives of triphenylene; a direct coupling of a 3,3',4,4'-tetraalkoxybiphenyl with alkoxyphenol produced monofunctionalized triphenylenes.     

Alignment behaviour of the discotic nematic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene on polyimide and cetyltrimethylammonium bromide coated substrates

The orientational behaviour of the nematic discotic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene (C8OBT) on substrates coated with a polyimide or cetyltrimethylammonium bromide (CTAB) was investigated by polarizing optical microscopy. The averaged order parameters and directions of the triphenylene core and the carbonyl groups of C8OBT were evaluated by an infrared dichroic method. The discotic nematic (N_D) phase of C8OBT exhibits a homeotropic alignment on a polyimide film, a typical nematic schlieren texture on a glass substrate, and a tilted or planar homogeneous alignment on a CTAB-coated substrate. The order parameter of the triphenylene core is higher on a polyimide film (S = 0.6) than on a CTAB-coated substrate (S = 0.2), whereas that of the carbonyl groups remains roughly constant at 0.2 to 0.3 independent of the substrate for the N_D phase.     

Vanadium oxytrichloride, a novel reagent for the oxidative trimerization of o-dialkoxybenzenes to hexaalkoxytriphenylenes

Triphenylene derivatives with six peripheral chains can make excellent discotic liquid crystals showing great promise in electronic devices. Vanadium oxytrichloride was found to be a novel reagent for the preparation of various triphenylene derivatives. Symmetrically substituted hexaalkoxytriphenylenes were obtained from o-dialkoxybenzenes by oxidative trimerization with VOCl₃ in high yields. Oxidative coupling of a 3,3',4,4'-tetraalkoxybiphenyl with 1,2-dialkoxybenzenes yielded unsymmetrically substituted derivatives of triphenylene; a direct coupling of a 3,3',4,4'-tetraalkoxybiphenyl with alkoxyphenol produced monofunctionalized triphenylenes.     

Synthesis of functionalized triphenylenes and dibenzopyrenes Precursor molecules for polymeric discotic liquid crystals

Discotic liquid crystals represent a promising class of new materials, for example, with respect to their photoconductivity properties. To tailor the processability and mesophase behaviour of such materials, specifically functionalized cores are required as precursor molecules for discotic oligomers, polymers and networks. The paper presents a simple synthetic strategy leading to unsymmetrically functionalized triphenylene and dibenzopyrene derivatives. Furthermore new symmetrical discotic octa-alkoxy-substituted dibenzopyrenes have been synthesized applying this route.     

Synthesis and characterization of star polymers initiated by hexafunctional discotic initiator through atom transfer radical polymerization

A novel hexafunctional discotic initiator, 2,3,6,7,11,12‐hexakis(2‐bromobutyryloxy)triphenylene (HBTP), was synthesized by the esterification of 2,3,6,7,11,12‐hexahydroxytriphenylene with 2‐bromobutyryl chloride. Atom transfer radical polymerizations of styrene, methyl acrylate, and n‐butyl acrylate were carried out in 50 vol % tetrahydrofuran with HBTP/copper(I) bromide/2,2′‐bipyridyl as an initiation system. The polymers produced had well‐controlled molecular weights and narrow molecular weight distributions (<1.2). On the basis of ¹H NMR spectra of the star polymer and its hydrolyzed products, we can conclude that the initiator quantitatively initiated the polymerization of vinyl monomers and that a star polymer with a discotic core was obtained. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2233–2243, 2001     

Charge transport properties in discotic liquid crystals: a quantum-chemical insight into structure-property relationships

We describe at the quantum-chemical level the main parameters that control charge transport at the molecular scale in discotic liquid crystals. The focus is on stacks made of triphenylene, hexaazatriphenylene, hexaazatrinaphthylene, and hexabenzocoronene molecules and derivatives thereof. It is found that a subtle interplay between the chemical structure of the molecules and their relative positions within the stacks determines the charge transport properties; the molecular features required to promote high charge mobilities in discotic materials are established on the basis of the calculated structure-property relationships. We predict a significant increase in the charge mobility when going from triphenylene to hexaazatrinaphthylene; this finding has been confirmed by measurements carried out with the pulse-radiolysis time-resolved microwave conductivity technique.     

氮杂苯并菲类n-型有机半导体材料研究进展

苯并菲盘状液晶是一类新型的有机电子学材料.该类材料多数以空穴传输功能为主,能传输电子的n-型材料较少.氮杂苯并菲是与苯并菲衍生物非常相似的一种杂环化合物,材料结构中引入了氮原子,吸电子能力得到增强,是潜在的n-型有机半导体材料,具有重要的应用价值.本文系统回顾了氮杂苯并菲类盘状液晶材料的研究进展,分类讨论了材料的分子结构,其中包括二、四、六氮杂苯并菲,以及它们的合成方法和物理化学性能,论述了材料在光电子领域的最新使用进展,并在此基础上,对该类液晶材料作为n-型有机半导体在光电子器件领域的应用前景进行了展望.     

Alignment behaviour of the discotic nematic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene on polyimide and cetyltrimethylammonium bromide coated substrates

The orientational behaviour of the nematic discotic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene (C8OBT) on substrates coated with a polyimide or cetyltrimethylammonium bromide (CTAB) was investigated by polarizing optical microscopy. The averaged order parameters and directions of the triphenylene core and the carbonyl groups of C8OBT were evaluated by an infrared dichroic method. The discotic nematic (N_D) phase of C8OBT exhibits a homeotropic alignment on a polyimide film, a typical nematic schlieren texture on a glass substrate, and a tilted or planar homogeneous alignment on a CTAB-coated substrate. The order parameter of the triphenylene core is higher on a polyimide film (S = 0.6) than on a CTAB-coated substrate (S = 0.2), whereas that of the carbonyl groups remains roughly constant at 0.2 to 0.3 independent of the substrate for the N_D phase.     

Effect of functionalization on glass formation by columnar mesophases of substituted triphenylene mesogens

Abstract

A new kind of discotic liquid crystal has been investigated where one out of the six ether side chains of a triphenylene core was replaced by an ester side chain. We have found greatly increased clearing temperatures and suppressed crystallization thus leading to glass forming discotics. Here we report the synthesis, X-ray and dielectric studies concerning the nature of the glass transition. Furthermore we give arguments as to why a ‘mixed’ substitution can lead to such drastic effects.     

The optical and charge transport properties of discotic materials with large aromatic hydrocarbon cores

The optical absorption and charge transport properties of a series of discotic molecules consisting of peripherally alkyl-substituted polycyclic aromatic cores have been investigated for core sizes, n, of 24, 42, 60, 78, 96, and 132 carbon atoms. In dilute solution, the wavelength maximum of the first absorption band increases linearly with n according to lambda(max) = 280 + 2n and the spectral features become increasingly broadened. The two smallest core compounds display a slight red-shift and increased spectral broadening in spin-coated films. For derivatives with n = 24, 42, 60, and 96, the one-dimensional, intracolumnar charge mobility, Sigma mu(1D), was determined using the pulse-radiolysis time-resolved microwave conductivity technique. For the compounds which were crystalline solids at room temperature, Sigma mu(1D) lay within the range 0.4-1.0 cm(2)/Vs. In the discotic mesophases at ca. 100 degrees C, Sigma mu(1D) was somewhat lower and varied from 0.08 to 0.38 cm(2)/Vs. The mobility values in both phases are considerably larger than the maximum values found previously for discotic triphenylene derivatives. However, the recently proposed trend toward increasing mobility with increasing core size is not substantiated by the results on the present series of increasingly large aromatic core compounds.     

Molecular properties and stacking of 1-substituted hexaalkoxy triphenylenes

In this work we consider the stability of columnar liquid crystals formed by discotic molecules differing only in one core substituent. In particular we concentrate on the 1-substituted 2, 3, 6, 7, 10, 11 hexaalkyloxy triphenylene family, and more specifically on the methoxy derivatives, studying the effects of seven α-substituents (H, Br, CH₃, Cl, F, NH₂, NO₂) on the shape and electronic properties, calculated at density functional level, and relating them with the phase behaviour of the corresponding hexyloxy derivatives. In a second step, we use the optimized structures and the atomic charges in a simplified Monte Carlo simulation of systems of molecules arranged in a columnar fashion, to try to shed light on the consequences of functionalization on the stacking behaviour.     

Electrophilic aromatic substitution in triphenylene discotics: Synthesis of alkoxynitrotriphenylenes

Functionalization of triphenylene-based discotic liquid crystals by direct nitration of hexaalkoxytriphenylene has very recently been reported to produce exclusively the mononitrohexaalkoxytriphenylene. W e have found that nitration of such discotics is not restricted to only one ring of triphenylene, but all the three rings can be nitrated successively to produce mononitro-, dinitro- and trinitro-hexaalkoxytriphenylenes. All the mononitro derivatives show a very broad mesophase range. While the dinitrohexabutyloxytriphenylene is non-liquid crystalline, its higher homologues are room temperature liquid crystals. Photomicroscopic pictures of these liquid crystalline materials show classical textures of an ordered hexagonal columnar phase. X-ray diffraction studies of two representative compounds, 4a and 4b, confirmed the above conclusions. None of the trinitro derivatives are liquid crystalline. Nitrotriphenylenes are valuable precursors to several other triphenylene derivatives like amino, acyl, alkylamino, diazo, etc. Mononitration of 2-hydroxy-3,6,7,10,11-pentaalkoxytriphenylenes gives the 1-nitro-2-hydroxy-3,6,7,10,11-pentaalkoxytriphenylenes. These double functionalized triphenylene derivatives are extremely important precursors as the functional group such as nitro, amino, azo, etc. can be utilized to modify the electronic nature of the core and at the same time the hydroxy functional group may be converted to a polymerizable group. Thus, processable oligomers and polymers can be synthesized.     

盘状液晶中间体单羟基苯并菲简便合成

羟基苯并菲[TP(OH)(OR)5]是一类重要的盘状液晶中间体. 根据苯并菲衍生物间极性差异, 设计了一条简便的合成与分离羟基苯并菲的方法: 在70%硫酸中用FeCl3氧化邻苯二醚与2-甲氧基苯酚三聚成环, 分离获得2,3,6,7,10,11-六烷氧基苯并菲[TP(OR)6]和2-羟基-3-甲氧基-6,7,10,11-四烷氧基苯并菲[TP(OH)(OMe)(OR)4]. 后者再经醚化, Ph2PLi脱甲基得2-羟基-3,6,7,10,11-五烷氧基苯并菲[TP(OH)(OR)5]. 三步反应总收率14%～19%.     

Oligomeric 1,3,5-triazines containing disc-shaped penta-alkyne and triphenylene side groups

A new type of discotic oligomer systems has been realized with either penta-alkyne or triphenylene side groups attached to amino substituted 1,3,5-triazine units in the main chain. The synthesis was carried out by reaction of 2,4-dichloro-1,3,5-triazine modified penta-alkynes and triphenylenes, respectively, with hexamethylene diamine. The discotic oligomers form stable edge-on oriented monolayers at the air/water interface. The mesophase structure of the novel discotic oligomers is characterized by an unusual lamellar layer arrangement. The mesogenic layer structure of the oligomeric triphenylenes changes to a rectangular columnar arrangement by charge transfer interaction with 2,4,7-trinitrofluorenone (TNF). Dielectric investigations were performed on the oligomeric triphenylene systems to analyse the influence of flexible segments on the internal mobility within the condensed state.     

Mesomorphic phase transition behaviour of photopolymerisable liquid crystalline triphenylene ether compounds

This report discusses the preparation and the unusual mesomorphism of three homologues of photopolymerisable triphenylene ether compounds. These homologues showed ‘a cold crystallisation’ on heating differential scanning calorimetry curves, and this phenomenon is attenuated with increase methylene units, spacers between the triphenylene core and the terminal photopolymerisable acrylate group. Classical textures of hexagonal columnar (Col_h) mesophase were observed by polarising optical microscopy for all three photopolymerisable mesophase compounds described here. Also described is the mesomorphism of their intermediates, hydroxylalkoxytriphenylenes. In some cases, the discotic columnar hexagonal mesophases were confirmed by wide angle X-ray scattering techniques.     

不对称苯并菲盘状液晶的合成及取代基对介晶性的影响

合成了一系列新型含间位二硝基苯甲酸酯不对称苯并菲盘状液晶化合物2-(3,5-二硝基苯甲酰氧基)-3,6,7,10,11-五烷氧基苯并菲(3a～3f). 通过偏光显微镜(POM)和差示扫描量热计(DSC)对其介晶性进行了研究. 结果显示: 此类化合物有高的清亮点, 稳定的六方柱状相以及较宽的介晶相范围, 且随着软链碳原子数的增加, 化合物的熔点和清亮点均出现下降趋势, 但六方柱状相的有序性却没有发生很明显的变化. 同时通过与其它三类苯并菲盘状液晶2-苯甲酰氧基-3,6,7,10,11-五烷氧基苯并菲(4a～4f), 2-二茂铁甲酰氧基-3,6,7,10,11-五烷氧基苯并菲(5a～5f), 2,3,6,7,10,11-六烷氧基苯并菲(6a～6f)的对比研究, 探讨了酯基, 强吸电子基团, 以及取代官能团体积对介晶性的影响. 证实了苯并菲化合物中分子结构小的变化将引起介晶性大的改变.     

Incorporation of liquid crystalline triphenylene derivative in bulk heterojunction solar cell with molybdenum oxide as buffer layer for improved efficiency

We report efficient bulk heterojunction solar cells fabricated by inserting a discotic triphenylene derivative into poly (3-hexylthiophene): [6, 6]- phenyl-C61-butyric acid methyl ester. A layer of molybdenum oxide was inserted between anode and active layer. Power conversion efficiency of 2.0% was achieved for these photovoltaic solar cells containing self-organised discotic liquid crystals in the active layer under one sun condition. The influence of varying the thickness of liquid crystal layer and annealing on these solar cells was also studied. Post annealing the bulk heterojunction devices with discotic liquid crystal layer of thickness 20 nm in them yielded an open circuit voltage of 0.41 V, short circuit current density of 17.0 mA cm^?2, a Fill factor of 0.35 and power conversion efficiency of 2.5%.     

Prediction, synthesis and investigation of mesomorphism of new octa(benzo-15-crown-5)-substituted derivatives of phthalocyanine and its metallo complexes [Zn(II), Ni(II)]

First calculation of molecular parameters (MP) of new octa-(benzo-15-crown-5)-substituted phthalocyanine derivatives and of its metallo complexes Zn(II), Ni(II) (Ib, Ic) is carried out. A prediction was made of the possible formation therefrom of metaphases, and for that purpose the synthesis of these compounds and investigation of their mesomorphic properties was performed. For compounds Ia-Ic the formation of high-temperature enantiotropic mesophases was established typical for discotic mesogenes, in good agreement with the prediction. Proceeding from the data on miscibility of 2,3,9,10,16,17,23,24-octa-[(4′-benzo-15-crown-5)-oxy]-phthalocyanine Ia with discotic mesogene 2,3,6,7,10,11-hexa(cyclohexanebenzoyloxy)triphenylene (II) displaying nematic mesomorphism the compound Ia was assigned to the group of nematic mesogenes and by the texture of the mixture to discotic mesogenes forming columnar type nematic phase (N _Col). Convergence of the results of prediction and experimental data is about 83%.     

First examples of functionalized triphenylene discotic dimers: molecular engineering of advanced materials

A series of novel functionalized triphenylene discotic dimers was synthesized starting from 2-hydroxy-3,6,7,10,11-pentaalkoxytriphenylene. Nitration of monohydroxypentaalkoxytriphenylene gave the mononitromonohydroxypentaalkoxytriphenylene which was alkylated with 2-bromoethanol. The resulting alcohol was coupled with various diacids. These compounds are unique in that they possess an electron withdrawing group (and consequently a large dipole moment) connected directly to the aromatic core. It is well known that connecting two discotic molecules together via a spacer (discotic dimers) stabilizes the columnar mesophase significantly and often leads to the formation of glassy materials. The introduction of functionality into LCs allows the variation of their properties on a wide scale and opens the route to new synthetic supramolecular systems for various device applications.