Liquid crystalline photoconductors

Closs, F.; Siemensmeyer, K.; Frey, Th.; Funhoff, D.

doi:10.1080/02678299308027741

Cited by 47 publications

(18 citation statements)

References 6 publications

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“…Since columnar discotic liquid crystals (LCs) show many extraordinary properties such as one-dimensional (1D) electrical conductivity, 2-5 fast photoconductivity [6][7][8][9][10][11] and ferroelectricity, 12,13 the structures and dynamics of discotic LCs have been studied extensively. Traditional columnar phases are normally constructed with discogenic (disc-like) molecules as building blocks which possess a rigid core with flexible tails (most of them are alkyl chains), and they usually exhibit three-, four-or six-fold rotational symmetry.…”

Section: Introductionmentioning

confidence: 99%

Phase behaviors and supra-molecular structures of a series of symmetrically tapered bisamides

et al. 2006

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A series of symmetrically tapered 1,4-bis[3,4,5-tris(alkan-1-yloxy)benzamido] benzene bisamides (CnPhBA, where n is the number of carbon atoms in the alkyl chains, n = 10, 12 and 16), was synthesized in order to investigate the effect of alkyl chain length on supra-molecular ordered structures induced by hydrogen (H)-bonding and micro-phase separation. These bisamides consist of a rigid aromatic bisamide core with three flexible alkyl chains at each end of the core. Major phase transitions and their origins in CnPhBA bisamides were studied with differential scanning calorimetry, one-dimensional (1D) wide angle X-ray diffraction (WAXD), infrared spectroscopy, and solid-state carbon-13 nuclear magnetic resonance experiments. The structures of these compounds in different phases were identified using 2D WAXD from oriented samples and were also confirmed by selected area electron diffractions in transmission electron microscopy from stacked single crystals and by computer simulations. All of the CnPhBA bisamides in this series formed a highly ordered oblique columnar (W OK ) phase and a low-ordered oblique columnar (W OB ) phase, similar to a recent report on C14PhBA.1 The two main driving forces in the formation of these two supra-molecular columnar structures were identified: One was the H-bond formation between N-H and CLO groups, and the other was the micro-phase separation between the bisamide cores and the alkyl chains. With increasing the length of alkyl tails, the isotropization temperature decreased, while the disordering temperature of the alkyl tails increased. The 2D lattice structures perpendicular to the columnar axis also increasingly deviated from the pseudohexagonal packing with increasing the alkyl tail length. However, the alkyl tail length did not have a significant influence on the packing along the columnar axis direction. Utilizing polarized optical microscopy, the phase identifications were also supported by the observation of texture changes and molecular arrangements inside of the micro-sized domains.

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Section: Introductionmentioning

confidence: 99%

Phase behaviors and supra-molecular structures of a series of symmetrically tapered bisamides

et al. 2006

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“…[1][2][3] Charge carrier mobilities are typically a few orders of magnitude lower than those for amorphous or crystalline molecular compounds. However, liquid crystals have the advantages that they are easier to process, free from grain boundaries, align spontaneously between electrodes, they are dynamic so that defects self-repair, and their conduction is highly anisotropic.…”

Section: Introductionmentioning

confidence: 98%

Photoconducting discotic liquid crystals

et al. 2003

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Molecular engineering of discotic liquid crystals is discussed with relation to charge carrier mobility and generation efficiency. Steady State DC and Pulsed TOF measurements are reported as viable complementary methods in the determination of charge generation efficiencies. Data for the quantum efficiencies of charge carrier generation in 2,3,6,7,10,11-hexa(hexyloxy)triphenylene and its 1:1 mixture with 2,3,6,7,10,11-hexakis(nonylphenyl)triphenylene (a complementary polytopic interaction (CPI) stabilized compound) are presented. The wavelength, field and temperature dependence of the quantum efficiency of charge carrier generation are discussed in respect of the Onsager theory of geminate recombination.

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“…The thermal behaviors of such monomeric and polymeric liquid crystals are well understood and consequently have been used as active media in display device technology [3]. They are also considered as potential candidates in applications involving information storage [4], nonlinear optics [5] and photoconductivity [6]. It is known that in both monomeric and polymeric liquid crystals (LCs), the shape of the anisometric entity determines the type of mesophase formed.…”

Section: Introductionmentioning

confidence: 99%

Monodispersive Unsymmetrical Tetramers Exhibiting a Columnar Phase

Yelamaggad

Nagamani

Hiremath

et al. 2003

Molecular Crystals and Liquid Crystals

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Oligomeric liquid crystals that are formed by joining two or more mesogenic segments axially through a flexible spacer (or multiple spacers) seem to be interesting materials from the points of view of both basic research and practical applications owing to their multifunctional characteristics and properties similar to those of polymers while retaining fluidity, viscosity etc. associated with those of low molar mass liquid crystals. The synthesis and evaluation of mesomorphic behavior of two novel monodispersive unsymmetrical tetramesogens have been presented here in detail. The molecular design of these tetramesogens incorporates the cholesteryl ester (as a chiral entity), biphenyl (as a supportive entity for mesomorphism), azobenzene (as a photoactive mesogen), and tolan (as a half-disc) segments interconnected through even-even-odd and odd-even-odd alkylene spacers. The target liquid crystalline tetramers have been realized by employing convenient synthetic strategies, which involves the preparation of two important unsymmetrical dimers and finally their condensation. The molecular structures of all the intermediates and unsymmetrical tetramers have been characterized by spectroscopic analyses. The mesomorphic property of both the unsymmetrical tetramers has been evaluated by optical microscopic, calorimetric and X-ray diffraction studies. Our study reveals that both oligomers show an identical mesophase. While X-ray studies suggest that the structure of the mesophase is similar to that of a rectangular columnar (Col r ) mesophase; a pseudoisotropic texture was seen under the microscope.

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Liquid crystalline photoconductors

Cited by 47 publications

References 6 publications

Phase behaviors and supra-molecular structures of a series of symmetrically tapered bisamides

Phase behaviors and supra-molecular structures of a series of symmetrically tapered bisamides

Photoconducting discotic liquid crystals

Monodispersive Unsymmetrical Tetramers Exhibiting a Columnar Phase

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