Discotic Liquid Crystals — A New Class of Fast Photoconductors

Adam, Dieter; Haarer, D.; Closs, F.; Frey, Th.; Funhoff, D.; Siemensmeyer, K.; Schuhmacher, Peter; Ringsdorf, Helmut

doi:10.1002/bbpc.19930971031

Cited by 54 publications

(23 citation statements)

References 33 publications

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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

405

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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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

405

417

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“…It exhibits an ordered hexagonal columnar liquid crystal phase (see Figure 1) between 69°C and 122°C in bulk and in sandwich cells it aligns quite easily with the columns perpendicular to the substrates . 27 Nanostructures of HAT5 were observed on substrates 28 but its strong tendency of forming elongated structures is apparent in the formation of very long wires that may spontaneously and uniformly align along a common direction , 29 although this is not always the case . 30 In this article we analyze the factors influencing the formation of HAT5 nanostructures on substrates, focusing on the effect of different solvents on the final organization and explaining the mechanism of formation of the 5 observed assemblies.…”

Section: Introductionmentioning

confidence: 96%

Ultralong Ordered Nanowires from the Concerted Self-Assembly of Discotic Liquid Crystal and Solvent Molecules

et al. 2015

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The realization of long, aligned molecular wires is a great challenge, and a variety of approaches have been proposed. Interestingly, hexapentyloxytriphenylene (HAT5) discotic liquid crystal molecules, a model system of molecules with flat and aromatic cores, can spontaneously form well-aligned, micrometer long, yet only tens of nanometers thick, nanowires on solid surfaces. We have investigated the formation mechanism of these wires using different solvents with selected characteristics, including chemical structure, boiling point, vapor pressure, and surface tension. When casting from toluene and benzene solutions, atomic force microscopy reveals that the discotics spontaneously form very long and thin wires, self-aligning along a common orientation. If instead dodecane or heptane are used, different and in general thicker structures are obtained. The chemical structure of the solvent appears to have a key role, coupling to the liquid crystal self-assembly by allowing solvent molecules to enter the ordered structure if their design matches the core of HAT5 molecules, thereby guiding the assembly. However, other aspects are also relevant in the assembly, including the nature of the substrate and the rate of solvent evaporation, and these can favor or interfere with the self-assembly into long structures. The use of solvents with aromatic structure is advantageous not only because it affects the geometry of the assembly, promoting long wire formation, but it is also compatible with good quality of the intermolecular order, as suggested by a high anisotropy of the Raman spectra of the nanowires formed from these solvents. Finally, the electrical properties of ordered systems show a clearly higher electrical conductivity compared to the disorganized aggregates.

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“…Single crystals exhibit very high mobility over 10 À1 -10 cm 2 =Vs indeed, but there remains unsolved problem of how to prepare large-area thin films for the device applications. Recently it was discovered that some type of liquid crystals, such as the discotic [5][6][7][8] and the smectic [9][10][11][12] having an aromatic p-conjugate moiety as a core part, exhibit very fast electronic conduction characterized by high mobility over 10 À2 cm 2 =Vs [11] and up to 0.1 cm 2 =Vs [6]. Now, liquid crystals are being recognized as a new class of organic semiconductors, i.e.…”

Section: Introductionmentioning

confidence: 99%

Charge Transport in Liquid Crystalline Semiconductor and Crosslinked Polymer Composite

Yoshimoto¹,

Funahashi²,

Hanna³

2004

Molecular Crystals and Liquid Crystals

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We have fabricated a novel charge carrier transport material composed of a liquid crystalline molecule and a cross-linked polymer. This composite system exhibited high hole mobility comparable with that of the pure liquid crystalline material. The charge carrier transport properties were influenced by the polymerization temperature, i.e., by the mesophase during polymerization. The hole mobility did not depend on temperature and electric field in the case of polymerized samples in the mesophase. We discussed the carrier transport properties in the polymer composites in comparison with those of the pure liquid crystalline material and the conventional polymer composite of the molecularly doped polymers, in addition to the resulting domain structures in the polymer composites with reference to the carrier transport properties in smectic mesophase as well as in the isotropic phase.

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Discotic Liquid Crystals — A New Class of Fast Photoconductors

Cited by 54 publications

References 33 publications

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

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

Ultralong Ordered Nanowires from the Concerted Self-Assembly of Discotic Liquid Crystal and Solvent Molecules

Charge Transport in Liquid Crystalline Semiconductor and Crosslinked Polymer Composite

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