Acta Phys. -Chim. Sin. ›› 2006, Vol. 22 ›› Issue (06): 764-767.doi: 10.3866/PKU.WHXB20060624

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Charge Trasport Properties in Discotic Liquid Crystals Made of the Extended-core m-phenylene Ethynylene Cycles

DING Fu-Jiang;ZHAO Ke-Qing   

  1. Department of Chemistry, Sichuan Normal University, Chengdu 610066, P. R. China
  • Received:2005-11-28 Revised:2006-02-13 Published:2006-05-31
  • Contact: DING Fu-Jiang

Abstract: Based on the semiclassical model of the charge transfer, kinetic parameters of the charge transfer reaction at the molecular scale in discotic liquid crystals made of the acetylene bridged macrocycle with benzene, acetylene bridged macrocycle with pyridine, butadiyne bridged macrocycle with benzene, butadiyne bridged macrocycle with pyridine have been studied at the level of B3LYP/6-31G(d) and B3LYP/STO-3G. Marcus theory indicates that the rate of charge hopping depends on two main parameters: the reorganization energy λ and the intermolecular transfer integral t. High transfer rates, and hence high charge mobilities, require small values for former and large values for the latter. The transfer integral t between cation and neutral molecule can be approximated by one half of the MO energy-splitting factor between the highest occupied molecular orbital and the next highest occupied molecular orbital at the transition state, where the two molecules adopt the same geometry. Our results prodict that the reorganization energies of the macrocycle molecules are much smaller than that of the triphenylene. The relative hole mobilities at room temperature (T=300 K) in the various macrocycle molecules and triphenylene have been calculated from the ratio of the corresponding transfer rates. Our results prodict that the hole mobility can be increased by up to 3 orders of magnitude when going from triphenylene to these macrocycle molecules. The significant improvement of the hole mobility in macrocycle molecules is mainly attributable to the smaller recoganization energy. The calculated charge mobility can hardly be predicted at the simple sight of a molecular structure, a theoretical approach has proved useful to design, prior to any chemical synthesis, discotic molecules with potentially high charge carrier mobilities.

Key words: Charge transfer, Discotic liquid crystal, Acetylene bridged macrocycle with benzene, Acetylene bridged macrocycle with pyridine, Quantum chemistry