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.     

2H NMR studies of phase behaviour and molecular motions of doped discotic liquid-crystalline systems

A discotic triphenylene monomer as well as a dimer and a main chain polymer, all substituted with heptyloxy side groups, were doped with an electron acceptor (2,4,7-trinitrofluorenone (TNF)) to give charge transfer complexes. These doped systems were aligned in a magnetic field, thus proving their liquid crystallinity. ²H NMR measurements show that the electron acceptor molecules are incorporated into the columns built of triphenylene cores. In the charge transfer complex with the triphenylene monomer almost all the electron acceptor molecules stack in the columns even close to the clearing temperature T₁, while for the dimer and especially for the polymer a significant fraction of the TNF molecules exhibits isotropic motion, which is attributed to their location in the region between the columns, already way below T₁. This isotropically distributed part increases on approaching T₁. Fast rotation of the discs around their column axes takes place in the monomer and is quenched in the dimer and the polymer, due to the interlinking of the columns by the spacer. The electron acceptor molecules, on the other hand, exhibit free rotation in all samples, even in the charge transfer complexes with the triphenylene dimer and polymer. In the side group labelled triphenylenes increased ²H NMR spectral narrowing is detected in the charge transfer complex samples compared with the corresponding pure triphenylenes. This indicates higher side group mobility in the doped systems, since the incorporation of TNF molecules increases the spacing between the discotic units.     

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.     

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.     

密度泛函理论研究边链对苯并菲电荷传输的影响

采用密度泛函理论在B3LYP/6-31G**水平上,根据电子转移的半经典模型对含有炔基的不同软链的苯并菲化合物分子的电荷传输性质进行研究。研究表明,所有目标化合物均有利于苯并菲的电荷传输。其中,直接在苯并菲刚性环上引入酰胺基（-CO-NH-）有利于提高正电荷的传输,而间隔基为酯基的单取代化合物的正负电荷传输性质均比较良好。在苯并菲上单取代的分子明显比其双取代、三取代的分子正电荷传输性质好。     

Discotic liquid crystalline poly(propylene imine) dendrimers based on triphenylene

The design, synthesis, and mesomorphic properties of a new series of homodendrimers consisting of the commercially available poly(propylene imine) (PPI) dendrimers (G = 1-5), PPI-(NH(2))(n)() (n = 4, 8, 16, 32, 64), functionalized with a discotic triphenylene moiety are reported. The liquid crystalline behavior was investigated by means of differential scanning calorimetry (DSC), polarizing-light optical microscopy (POM), and X-ray diffractometry (XRD). All of the homodendrimers showed mesomorphic properties, with the second to fifth generations giving a hexagonal columnar mesophase (Col(h)) and the first generation a rectangular columnar mesophase (Col(r)). The X-ray study reveals that these mesophases show a highly ordered structure with segregation of triphenylenes and dendrimers into separate columns and a regular stacking distance inside the triphenylene columns. GPC analysis showed that the dendrimers had good monodispersity and MALDI-TOF studies of the first three generations gave good evidence that all of the terminal amino groups of the dendrimers were functionalized with a discotic unit.     

Eutectic mixtures with plastic columnar discotics: molecular structure,phase morphology and kinetics of phase separation

We report the properties of eutectic mixtures of triphenylenes displaying a highly ordered columnar phase with a low molar mass non‐discotic compound. Such highly ordered triphenylenes display large charge carrier mobilities which are strongly controlled by the state of order in the discotic phase. The motivation was to establish how the state of order—molecular order, phase morphology, temperature ranges of phase stabilities and macroscopic orientational order—can be influenced by mixing. The studies reveal that the molecular order, in particular the mutual arrangement of the columns and the intracolumnar order, are unaffected by dilution of the discotic compound, whereas the phase morphology and the kinetics of phase separation change significantly with dilution. Rod‐shaped discotic domains with a hexagonal cross‐sectional area are formed via a nucleation process and the rods grow linearly as a function of time. Both the pure discotic phase as well as the discotic domains forming during phase separation can be macroscopically ordered by orientation layers.     

Novel discotic liquid crystal oligomers: 1,3,5-triazine-based triphenylene dimer and trimer with wide mesophase

Series of novel 1,3,5-triazine-based triphenylene oligomers 7, 10 and 12 with large bridging polyaromatic core were designed and synthesised by simple procedures in high yields. Their structures were confirmed by FTIR, ¹H NMR, ESI-MS and elemental analyses. Their mesomorphic behaviours were studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. 1,3,5-triazine-based triphenylene monomer 7 has no mesomorphic property, but 1,3,5-triazine-based triphenylene dimer 10 and 1,3,5-triazine-based triphenylene trimer 12 possess excellent mesomorphic properties. The mesomorphic temperature range of compound 12 was as wide as 180°C. These studies indicated that the mesomorphic properties were determined by the numbers of triphenylene units. More units of triphenylene in the oligomers resulted in better mesomorphic properties.     

Eutectic mixtures with plastic columnar discotics: molecular structure, phase morphology and kinetics of phase separation

We report the properties of eutectic mixtures of triphenylenes displaying a highly ordered columnar phase with a low molar mass non-discotic compound. Such highly ordered triphenylenes display large charge carrier mobilities which are strongly controlled by the state of order in the discotic phase. The motivation was to establish how the state of order—molecular order, phase morphology, temperature ranges of phase stabilities and macroscopic orientational order—can be influenced by mixing. The studies reveal that the molecular order, in particular the mutual arrangement of the columns and the intracolumnar order, are unaffected by dilution of the discotic compound, whereas the phase morphology and the kinetics of phase separation change significantly with dilution. Rod-shaped discotic domains with a hexagonal cross-sectional area are formed via a nucleation process and the rods grow linearly as a function of time. Both the pure discotic phase as well as the discotic domains forming during phase separation can be macroscopically ordered by orientation layers.     

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．     

Discotic liquid crystalline tris(hexahexyloxytriphenylene)triazines with separate columns of triphenylene and triazine cores

A series of novel discotic liquid crystal compounds containing three pendent triphenylenes connected to a triazine core via spacers of different length that were linked via a triazole group as obtained from an azide–alkyne click reaction was investigated. All compounds of the series exhibit wide-range columnar phases from room temperature to more than 100°C. X-ray reflection measurements indicate an ordering with separate columns of the triazine and triphenylene cores. Quantum chemical calculations confirmed the significant contributions of the triazine and triazole groups to the π–π stacking in the columns. This type of organisation reveals an additional feature of triazole-forming click chemistry and indicates interesting properties for optoelectronic applications.     

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.     

含氟链不对称苯并菲盘状液晶的合成及疏氟效应对介晶性的影响

盘状液晶分子中引入氟代烃链并利用疏氟效应（fluorophobic effect）能有效稳定分子的柱状堆积;低对称性的盘状分子有较低的熔点和宽的介晶相温度范围．基于此,本文设计并合成了一系列半氟酯链的不对称苯并菲化合物C18H6（OCnH2n＋1）4（OCH3）（O2CC2H4C6F13）（1）,及相对应的不含氟化合物C18H6（OCnH2n＋1）4（OCH3）（O2CC8H17）（2）,n=4—8．化合物结构通过核磁和质谱表征．介晶性通过差示扫描量热法和偏光显微镜进行了研究．结果显示：化合物均为柱状互变热致液晶．含氟链化合物1a—1e与相对应的化合物2a-2e比较,有更高的熔点和清亮点．合成的多数化合物为室温液晶．     

Discotic triphenylene twins linked through thiophene bridges: controlling nematic behavior in an intriguing class of functional organic materials

Substituted triphenylenes and similar discotic molecules have a strong tendency toward columnar organization. Nematic mesophases are much less commonly observed in discotic systems. We have demonstrated a general strategy whereby discotic triphenylenes can be twinned to form stable, boardlike materials that display only nematic mesophases. The dominant structural feature that leads to nematic behavior is an enforced void region in the center of the macrocycle that results from bridging through the triphenylene 3,6-positions. This precludes simple columnar assembly because it would lead to free space through the center of each stack. Selection of appropriate bridging units allows materials to be designed which combine molecular features, such as the optoelectronic properties of electron-rich triphenylenes and conjugated thiophene units, with the processability, self-healing, and alignment features inherent in nematic mesophases. In addition, communication across twinned structures can lead to additional enhancement of optoelectronic behavior. This is particularly apparent in fully conjugated, planar twin 12 which is formally expected to have some antiaromatic character. This character is manifested in its spectral properties, and particularly noteworthy is its strong, Stokes shifted emission at around 500 nm.     

Novel fluorescent liquid crystals: synthesis,mesomorphism and fluorescence of triphenylene-Bodipy derivatives based on 1,3,5-triazine core

The novel triphenylene-Bodipy derivatives 6 and 7 based on 1,3,5-triazine core were designed and synthesised by introducing BODIPY unit and triphenylene units sequentially onto cyanuric chloride. The Bodipy derivative 6 with one triphenylene unit was a nematic liquid crystal but the derivative 7 with two triphenylene units was a hexagonal columnar liquid crystal. The investigation on photophysical properties suggested that both of them exhibited excellent fluorescence with high fluorescence quantum yields and the Stokes shifts were larger than their Bodipy precursors. This research presented a good example of design and synthesis of columnar Bodipy liquid crystal with high fluorescence and large Stokes shift.     

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)     

Preliminary communication First example of a functionalized triphenylene discotic trimer: molecular engineering of advanced materials

A new type of functionalized discotic oligomer system has been realized whose molecular architecture consists of a trisubstituted benzene as central core and three nitro-functionalized triphenylenes as regional cores. These regional cores are linked to the central core via ether linkages through an alkyl chain spacer. Polarizing microscopy and calorimetric measurements reveal the existence of a monotropic columnar mesophase in this novel functionalized oligomer. The product does not crystallize at room temperature over a long period ( c. five months) or on cooling to 50 C. The corresponding unfunctionalized trimer is not liquid crystalline. The dipolar interaction of nitro groups is probably responsible for the induction of mesogenicity. The introduction of functionality into liquid crystal oligomers permits the variation of their properties on a wide scale and opens the route to new synthetic supramolecular systems for various device applications.     

Preliminary communication First example of a functionalized triphenylene discotic trimer: molecular engineering of advanced materials

A new type of functionalized discotic oligomer system has been realized whose molecular architecture consists of a trisubstituted benzene as central core and three nitro-functionalized triphenylenes as regional cores. These regional cores are linked to the central core via ether linkages through an alkyl chain spacer. Polarizing microscopy and calorimetric measurements reveal the existence of a monotropic columnar mesophase in this novel functionalized oligomer. The product does not crystallize at room temperature over a long period (c. five months) or on cooling to 50 C. The corresponding unfunctionalized trimer is not liquid crystalline. The dipolar interaction of nitro groups is probably responsible for the induction of mesogenicity. The introduction of functionality into liquid crystal oligomers permits the variation of their properties on a wide scale and opens the route to new synthetic supramolecular systems for various device applications.     

Synthesis of monohydroxy-functionalized triphenylene discotics: green chemistry approach

This paper presents an environmentally benign procedure for the preparation of monohydroxy-functionalized triphenylenes using simple ionic reagents. Pyridinium hydrochloride, pyridinium hydrobromide, N-methyl pyridinium iodide, N-ethyl pyridinium bromide, and 1-n-butyl-3-methyl imidazolium bromide have been employed to prepare various monohydroxypentaalkoxytriphenylenes, which are valuable precursors for the synthesis of a variety of discotic monomers, dimers, oligomers, and polymers.     

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%.