Highly photoconductive discotic liquid crystals Structure–property relations in the homologous series of hexa-alkoxytriphenylenes

Bengs, Holger; Closs, F.; Frey, Th.; Funhoff, D.; Ringsdorf, Helmut; Siemensmeyer, K.

doi:10.1080/02678299308036478

Cited by 67 publications

(30 citation statements)

References 26 publications

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“…cos a, cos a, -sin a, sin a,) (16) where the angles al and a2 are defined in Figure 11; the intercolumnar hopping probability in the xy plane is K (2 cos a, cos a, -sin a, sin a,)2 (17) R 6 p (R,a,,cc2) = By taking the average of p (R,al,a2) over all the angles al and a2, we find:…”

Section: Monte Carlo Simulationsmentioning

confidence: 99%

Triphenylene Columnar Liquid Crystals: Excited States and Energy Transfer

Markovitsi¹,

Germain²,

Millié³

et al. 1995

J. Phys. Chem.

169

200

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The present paper deals with the photophysical properties of columnar liquid crystals formed by hexakis-(alky1oxy)triphenylenes. Absorption and fluorescence spectra of solutions are analyzed on the basis of quantum chemical calculations performed by the CS-INDO-CI (conformations spectra-intermediate neglect of differential overlap-configuration interaction) m e t h d . the absorption maximum is due to the SO -Sq transition while fluorescence originates from the weak SO -S1 transition. In columnar aggregates, the former transition corresponds to delocalized excited states while the latter corresponds to localized ones; calculation of intermolecular interactions shows that, at the temperature domain of the mesophases, all the molecules have the same excitation energy and, therefore, no spectral diffusion of the fluorescence is expected, in agreement with the time-resolved emission spectra. Excitation transfer is investigated by studying the fluorescence decays of mesophases doped with energy traps. Their analysis is made by means of Monte Carlo simulations considering both intracolumnar and intercolumnar jumps and using four different models for the distance dependence of the hopping probability. The best description is obtained with a model based on the extended dipole approximation and taking into account molecular orientation.

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Section: Monte Carlo Simulationsmentioning

confidence: 99%

Triphenylene Columnar Liquid Crystals: Excited States and Energy Transfer

Markovitsi¹,

Germain²,

Millié³

et al. 1995

J. Phys. Chem.

169

200

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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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“…1.͒ Of particular relevance to their possible use in electronic device applications are charge carrier mobility measurements. Experimental mobility values have been obtained from time-of-flight ͑TOF͒ measurements, [5][6][7][8][9][10][11][12][13] pulseradiolysis time-resolved microwave conductivity ͑PR-TRMC͒ measurements 14 -20 and frequency dependent AC conductivity measurements on doped samples. [21][22][23][24] The conductivity in triphenylene derivatives is mainly due to transport of positive charges ͑holes͒ and for the liquid crystalline phase mobility values in the range 10 Ϫ3 -10 Ϫ1 cm 2 V Ϫ1 s…”

Section: Introductionmentioning

confidence: 99%

Charge transport in columnar stacked triphenylenes: Effects of conformational fluctuations on charge transfer integrals and site energies

Senthilkumar

Grozema

Bickelhaupt

et al. 2003

The Journal of Chemical Physics

408

417

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Values of charge transfer integrals, spatial overlap integrals and site energies involved in transport of positive charges along columnar stacked triphenylene derivatives are provided. These parameters were calculated directly as the matrix elements of the Kohn-Sham Hamiltonian, defined in terms of the molecular orbitals on individual triphenylene molecules. This was realized by exploiting the unique feature of the Amsterdam density functional theory program that allows one to use molecular orbitals on individual molecules as a basis set in calculations on a system composed of two or more molecules. The charge transfer integrals obtained in this way differ significantly from values estimated from the energy splitting between the highest occupied molecular orbitals in a dimer. The difference is due to the nonzero spatial overlap between the molecular orbitals on adjacent molecules. Calculations were performed on unsubstituted and methoxy-or methylthio-substituted triphenylenes. Charge transfer integrals and site energies were computed as a function of the twist angle, stacking distance and lateral slide distance between adjacent molecules. The variation of the charge transfer integrals and site energies with these conformational degrees of freedom provide a qualitative explanation of the similarities and differences between the experimental charge carrier mobilities in different phases of alkoxy-and alkylthio-substituted triphenylenes. The data obtained from the present work can be used as input in quantitative studies of charge transport in columnar stacked triphenylene derivatives.

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Highly photoconductive discotic liquid crystals Structure–property relations in the homologous series of hexa-alkoxytriphenylenes

Cited by 67 publications

References 26 publications

Triphenylene Columnar Liquid Crystals: Excited States and Energy Transfer

Triphenylene Columnar Liquid Crystals: Excited States and Energy Transfer

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

Charge transport in columnar stacked triphenylenes: Effects of conformational fluctuations on charge transfer integrals and site energies

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