The carrier transport properties of a molecularly diluted smectic liquid crystalline photoconductor, 2-(4′-octylphenyl)-6-dodecyloxynaphthalene (8-PNP-O12) and 2-(4′-hexyoxy)-6-octypbiphenyl (6O-BP-8) system, were investigated by time-of-flight technique, in order to clarify the nature of electronic conduction in the liquid crystalline mesophases. The mobility in the diluted liquid crystals was ambipolar, independent of both electric field and temperature in SmA and SmB phase as in the pure 8-PNP-O12, and continuously reduced with an increase in the diluent concentration. The reduction, however, remained within a small range of one third of that of pure material even in 60 mol%. The carrier transport in the diluted liquid crystals was described by the relation of a μ/2 ∝ exp(-2 ρ/ρ0), where μ is the mobility, ρ the average hopping distance, and ρ0 a wavefunction decay constant of molecular orbital, indicating the 2-dimentional random hopping mechanism. The fairly large ρ0 of 2.3 ∼ 2.4 A characterizes a fast mobility gently decreasing with an increase in the diluent concentration. The molecular ordering within a smectic layer did not affect the carrier transport properties at all except the initial difference of the mobility, as far as comparison of those in SmA and SmB phases were concerned. In addition, the effect of self-organization of hopping site is discussed in terms of carrier transport in disorded materials system.
K. Kurotaki, J.-I. Hanna, "Carrier Transport in Molecularly Diluted Liquid Crystalline Photoconductor" in Journal of Imaging Science and Technology, 1999, pp 237 - 241, https://doi.org/10.2352/J.ImagingSci.Technol.1999.43.3.art00008