Novel triphenylenoimidazole discotic liquid crystals

A novel discotic core was constructed by fusing imidazole unit with well-known triphenylene discotic core. Two new imidazole fused unsymmetrically substituted triphenylene derivatives were prepared and characterized. While the molecular structures of the new compounds were verified by ¹H NMR, UV, MS and elemental analysis, their liquid crystalline properties were determined by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction studies. These triphenylenoimidazole derivatives were found to exhibit hexagonal columnar mesomorphism over a wide temperature range.     

Synthesis, structures and optical properties of trisilasumanene and its related compounds

Novel trisilasumanenes that have no substituents on the exo carbon atoms, silicon analogues of sumanene, were prepared via repetitive lithiations of triphenylene followed by introduction of silicon functionalities. The optical properties of these trisilasumanenes and their related compounds were investigated by UV-vis and fluorescence spectroscopy.     

Polysubstituted triphenylenes with active groups. Molecular parameters, synthesis, structure, and mesomorphism

Molecular parameters of hexaalkoxytriphenylenes with different substituents on the periphery of the triphenylene nucleus of known and hypothetical structures are calculated. The probability of a discophase for compounds of this series is estimated from molecular parameters. Several compounds of this series having polar groups (NO₂, NH₂) in the 1 position of the triphenylene nucleus have been synthesized. The compounds synthesized were investigated by thermopolarizing microscopy and X-ray diffraction analysis. The data on the mesomorphism of the new compounds are in good agreement with our prediction that alkoxytriphenylenes with polar groups have a discophase. It is established that introduction of an electron-accepting group at position 1 of the triphenylene nucleus expands the temperature range of existence of the discophase to room temperature. On the contrary, introduction of an electron-donating group narrows this interval. Compounds of this series presumably have a hexagonal columnar structure. Ivanovo State University. Warsaw University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 464–472, May–June, 1998. This work was supported by RFFR grant No. 96-02-19036.     

Synthesis and investigation of triphenylene discotic derivatives with donor and acceptor groups and with predictable type of mesomorphism

Prognosis of columnar mesomorphism is performed, five new hexa-and hepta-substituted triphenylene derivatives with donor and acceptor groups are synthesized and their mesomorphoc properties are stusied. Good agreement is achieved between predictions and experiments. The synthesized triphenylene derivatives are found to display enantiotropic columnar mesomorphism. 1-Amino-2,3,6,7,10,11-hexaheptyl-xytriphenylene anilides of 2,3,5-triiodo-, 3,4,5-trihydroxy-and 4-nitro-benzoic acids reveal enantiotropic dimesomorphism. Also found decrease in thermal stability and extension of the interval of existence of mesophase at introduction to triphenylene frame of substituents with acceptor groups at the amino group.     

Iodo-substituted triphenylene-based discogens: by metal-mediated oxidative cross-coupling

New monoiodopentakis(alkoxy)triphenylene derivatives were synthesized and characterized. The metal-mediated oxidative coupling of 2-iodoalkoxybenzene with 3,3',4,4'-tetraalkoxybiphenyl by MoCl₅ as oxidizing reagent yields 2-iodopentakis(alkoxy)triphenylene. These products were purified by repeated column chromatography; their liquid crystalline properties were studied by polarizing optical microscopy and differential scanning calorimetry. All the derivatives exhibit a columnar mesophase over a wide temperature range.     

Synthesis and the effects of substitution upon photochromic diarylethenes bearing an isoxazole moiety

A new class of unsymmetrical photochromic diarylethenes bearing an isoxazole moiety was synthesized and the effects of substitution on their optical and electrochemical properties were investigated systematically. Each of the compounds exhibited remarkable photochromism and functioned as a fluorescent photoswitch both in solution and in poly(methyl methacrylate) films. The electron-donating substituents effectively shifted the absorption maximum and the emission peak to a longer wavelength direction, while the electron-withdrawing substituents notably enhanced the fluorescent quantum yields and oxidation onsets of these diarylethene derivatives. As compared to the unsubstituted parent diarylethene, introduction of the electron-donating/withdrawing substituents could efficiently modulate the optical and electrochemical properties of the diarylethenes bearing an isoxazole moiety. All results indicated that the isoxazole moiety and the substitution effects played a very important role during the process of photochromic reaction for these diarylethene derivatives.     

Theoretical study on the charge transport properties of triphenylene discogens with a phenylpropionyloxy or 3-phenylpropenoyloxy side chain

Charge transport is one of the most important properties in organic materials. Charge transport properties of triphenylene discogens with a phenylpropionyloxy or 3-phenylpropenoyloxy side chain have been investigated computationally on the basis of semi-classical Marcus theory. The results show that three triphenylene derivatives have high charge mobility. Title compounds have much better electronic mobility than the triphenylene. The triphenylenes containing 3-phenylpropenoyloxy have better hole mobility, but smaller electronic mobility than the triphenylenes with phenylpropionyloxy. For the triphenylene discogens with a phenylpropionyloxy, the longer the alkloxy chains, the better the positive charge transfer rate, but the smaller the negative charge transfer rate. Supported by the National Natural Science Foundation of China (Grant No. 50673069), the Research Foundation of Education Bureau of Sichuan Province, China (Grant No. 07ZA093), and Scientific Research Foundation of Sichuan Normal University for Innovation Groups ( Grant No. 025156)     

Iodo‐substituted triphenylene‐based discogens: by metal‐mediated oxidative cross‐coupling

New monoiodopentakis(alkoxy)triphenylene derivatives were synthesized and characterized. The metal‐mediated oxidative coupling of 2‐iodoalkoxybenzene with 3,3′,4,4′‐tetraalkoxybiphenyl by MoCl₅ as oxidizing reagent yields 2‐iodopentakis(alkoxy)triphenylene. These products were purified by repeated column chromatography; their liquid crystalline properties were studied by polarizing optical microscopy and differential scanning calorimetry. All the derivatives exhibit a columnar mesophase over a wide temperature range.     

Observation of intercalated smectic phases in symmetric liquid crystal dimers containing hydrazide groups

Dimeric hydrazide derivatives with nitro, phenyl, and methyl terminal subsistents were synthesized. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and wide angle X-ray diffraction. Interestingly, intercalated smectic phases were observed in these symmetric liquid crystal dimers. The effect of the substituents and the length of the spacer on the mesophase is discussed, confirming that intermolecular hydrogen bonding between the hydrazide groups was the driving force for the formation of the intercalated structures.     

Synthesis and characterization of liquid crystalline unsymmetrically substituted phthalocyanines

The synthesis of unsymmetrically substituted phthalocyanines bearing two p-tolyl-sulfonyl (tosyl)amido and six alkylthio moieties was achieved by cyclotetramerisation of two different phthalonitrile derivatives, namely 1,2-di(alkylthio)-4,5-dicyanobenzene and 4,5-dicyano-N,N′-ditosyl-o-phenylenediamine in the presence of an anhydrous metal salt and strong base. The new compounds were characterized by elemental analyses, UV/Vis, IR, NMR and mass spectra. The mesogenic properties of these new materials were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy. The mesogenic properties of these compounds were compared to that of their symmetric analogous, octaalkythia substituted phthalocyanine derivatives.     

Absorption and luminescence spectra of electroluminescent liquid crystals with triphenylene,pyrene and perylene units

New derivatives of triphenylene, perylene, and pyrene are described, some of which form columnar mesophases. The absorption spectra are investigated both experimentally and theoretically. The spectra calculated using the density functional tight binding (DFTB) theory are in good agreement with experimental results. The investigated compounds show photoluminescence of violet-blue (triphenylene), yellow-green (pyrene), and orange-red (perylene) colours. In addition, electroluminescence is observed in thin films of these compounds between a positively charged ITO electrode and a negatively charged aluminium electrode. The brightness of the electroluminescence decreases in the order perylene > pyrene > triphenylene. Threshold voltages below 20 V and a luminance up to 100 cd m^-2 were observed.     

苯丙炔酸和苯丙烯酸酯苯并菲盘状液晶电荷传输的理论研究

电荷传输是有机材料的重要性质之一．根据电子转移的半经典模型对含苯丙炔酸和苯丙烯酸酯支链的苯并菲盘状液晶化合物分子的电荷传输性质进行理论研究．研究结果表明,所计算的三个苯并菲衍生物分子均具有高的电荷传输性能．标题化合物分子的负电荷传输速率均比苯并菲大,含苯丙烯酸酯链的苯并菲分子比含苯丙炔酸酯链的苯并菲分子具有较大的空穴传输速率及较小的负电荷传输速率．对于含苯丙烯酸酯链的苯并菲分子,链烷氧基越长,正电荷传输速率越大,负电荷传输速率越小．     

Synthesis and liquid crystal properties of triphenylene liquid crystals bearing polymerisable acrylate and methacrylate groups

The synthesis and liquid crystalline properties of some new triphenylene discotics bearing pendant acrylate groups are described. Mesophase behaviour is found to be sensitive to the number and position of substituents, the linking chain length, and to change between acrylate and methacrylate termini. Investigation of the isomerically pure triphenylene acrylate and methacrylate derivatives showed that the molecular symmetry also has a modest effect on mesophase behaviour. Unsurprisingly columnar phases are formed only when all substituent chains are of comparable length and methacrylates are far superior to simple acrylate termini, probably due to favourable space filling in the mesophase.     

Synthesis of dehydrobenzo[18]annulene derivatives and formation of self-assembled monolayers: implications of core size on alkyl chain interdigitation

The synthesis of a series of dodecadehydrotribenzo[18]annulene ([18]DBA) derivatives is reported, together with their steady-state absorption and fluorescence properties. The main focus, though, is on the self-assembly of these compounds at the liquid-solid interface as investigated with scanning tunneling microscopy (STM), highlighting the effect of alkyl chain orientation and alkyl chain length on the molecular ordering. Owing to the large triangular pi-electron system of the [18]DBAs, two different types of alkyl chain orientation are observed. The observed changes in the monolayer networks upon elongation of the alkyl chains are attributed to the increased van der Waals interactions between molecules and substrate. The effect of the core size on the alkyl chain orientation and, as a result, the monolayer structure is discussed in relation to the results obtained previously for triangularly-shaped dehydrobenzo [12]annulene ([12]DBA) derivatives and triphenylene derivatives. A guideline for substituent spacing allowing control of molecular alignment for large planar pi-electron systems utilizing directional alkyl chain interdigitation is also discussed.     

2-(4-Biphenylyl)-1,3,4-oxadiazoles: synthesis and mesogenic studies

A series of 2-(4-biphenylyl)-1,3,4-oxadiazoles bearing alkyl or alkoxy substituents at the 4? position, and a hydrogen, or alkyl substituent (linear, branched, fluorinated or functionalised) at the 5 position were synthesised and characterised (51 compounds). Their mesogenic properties were evaluated using differential scanning calorimetry and polarising optical microscopy. Results show that substitution of the 1,3,4-oxadiazole ring for a terminal benzene ring in a conventional p-terphenyl enriched the mesogenic properties. Most of the new oxadiazole compounds exhibit either monotropic or enantiotropic smectic A mesophases with widths ranging from 3 to 50°C. A few compounds (short tailed) exhibit nematic phases and some compounds with branched or fluorinated alkyl substituents at the 5 position are also mesogenic.     

Synthesis and characterisation of benzoxazole-based liquid crystals possessing 3,5-difluorophenyl unit

Series of fluorinated compounds, 2-(3′,5′-difluoro-4′-alkoxybiphenyl-4-yl)-benzoxazole derivatives (nFBx), were prepared and characterised. Their phase transition behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. In the case of carbon atoms in the alkoxy chain between 4 and 10, they exhibited enantiotropic mesophases with the mesophase ranges of 12–119°C and 23–152°C on heating and cooling for compounds bearing different substituents (H, CH₃, Cl, and NO₂). With the exception of nitro-substituted compounds, the nFBx series displayed intense photoluminescence emission at 380–385 nm in methylene chloride solution when they were excited at their absorption maxima. Compared to non-fluorinated analogues, fluorinated compounds nFBx (apart from nitro-substituted compounds) exhibited much lower melting points, but comparable or slightly narrower mesophase ranges during both heating and cooling, which were attributed to the disruption of the side-to-side intermolecular packing caused by the two lateral fluoro substituents.     

含胆固醇和 4-(反式-正烷基环己基)苯甲酸结构单元的双液晶基元液晶化合物的合成及其性质

本文合成了一系列含有胆固醇和4-（反式-正烷基环己基）苯甲酸结构单元的新型双液晶基元液晶化合物。这些化合物中两个介晶基元是利用不同长度的氧烷酰基连接在一起。利用FT-IR、MS、1H NMR、POM、DSC 表证了所得化合物的结构和介晶性,并选择几种双液晶基元液晶测定了它们的机械黏度和在主体液晶中的螺旋扭曲力（HTP)。结果表明,绝大多数化合物显示较低相变温度的胆甾相（N*）,并且被选择的化合物的平均机械黏度和螺旋扭曲力类似于或优于胆甾醇任酸酯。     

Photochromism of new 3,5-position hybrid diarylethene derivatives bearing both thiophene and thiazole moieties

Five new diarylethenes based on a hybrid structure of bis(5-thiazolyl)ethene and bis(3-thienyl)ethene were synthesized, and the structures of the four compounds were determined by single-crystal X-ray diffraction analysis. The properties of these diarylethenes, such as photochromism, fluorescence, and electrochemical properties were investigated in detail. All of these compounds showed good photochromism and fluorescence both in solution and in PMMA films. The electron-donating substituents could effectively increase the cyclization and cycloreversion quantum yields, and the fluorescence emission peaks, whereas the electron-withdrawing groups functionalized an inverse action for these diarylethene derivatives. Cyclic voltammetry revealed that great differences existed amongst the electrochemical behaviors of these compounds. The oxidation potentials and the band gaps of these diarylethenes increased remarkably with the increase in electron-withdrawing ability. All results suggested that the effects of substitution have a significant effect on the photochemical and electrochemical behaviors of these diarylethene derivatives.     

The influence of structural changes of the N‐substituent on liquid crystalline behaviour of ester imides

Several new ester imide derivatives with different N‐substituents in the imide ring were synthesized and their mesogenic properties investigated by thermal analysis, optical microscopy and X‐ray diffraction. All the esters of N‐4‐[(4′‐decyloxybiphenyl‐4‐yl)oxycarbonyl]phthalimideacetic acid and aliphatic alcohols exhibited monolayer SmA and SmC phases. In addition, for the ethyl and propyl esters a monotropic hexatic (F or I) phase was observed. The introduction of additional substituents at the carbon atom in the methylenemethoxycarbonyl group (in the vicinity of the nitrogen atom) substantially influenced liquid crystalline properties: the compounds with a flexible chain exhibited monotropic SmA–SmB dimorphism, but liquid crystalline properties vanished for the substituent containing the more rigid phenyl ring.     

Core-halogenated,helical-chiral triphenylene-based columnar liquid crystals

It is shown that chlorination and even bromination of the mesogenic hexahexyloxytriphenylene 1 can take place at the sterically congested tetracyclic core delivering the respective monohalogenated, sevenfold substituted enantiotropic mesogens 3 and 4 in 32 and 17% yields, respectively, giving mesophases over greater temperature ranges. Miscibility tests among all mesogenic compounds of this study prove formation of the columnar hexagonal type of phase. The steric and electronic effects of those substituents, different from the six equal alkoxy groups, on the mesophase are discussed in detail. In our hands and to our surprise, the sterically hindered acceptor (nitro or halogeno) substituents of 2, 3, or 4 could not be replaced by an alkylthio group in nucleophilic aromatic substitution reactions using the aprotic polar solvent DMEU. Semi-empirical calculations on numerous hexaethers with one or two substituents, e.g. halogens or others, in one of the three bay regions of the triphenylene core reveal that these molecules are helically deformed due to the crowding in the molecule. In this new case of atropisomerism, the 1,12-disubstituted derivatives should offer the possibility of resolution into enantiomers and, therefore, of studying disc-like mesomorphic compounds possessing for the first time the origin of chirality within their molecular centre.