Photoconductivity of Discotic Liquid Crystals Derived from A Long-Chain Tetraphenylporphyrin

Abstract

ABSTRACTPhotoconductivity of a mesogenic tetraphenylporphyrin (TPP) is shown in relation to the mesomorphic phase transition behavior. The TPP mesogen shows two types of mesophases having smectic-like order (lamellar mesophases : DL and DLC phases named in this work) and the photocurrent changes stepwise at the phase transitions with non-Arrhenius dependence whilst the darkcurrent tends to be Arrhenius. The hole mobility was measured for the random domain cell and was found to be faster than 10−4 cm2v−1sec−1 in the mesophases. The cell used for the photocurrent measurements was a sandwich-type one using two ITO glass slides as electrtodes and show rectification behavior for the crystal and the low-temperature mesophase (DLC) in contrast to non-rectification of photocurrent in the high-temperature mesophase (DL). These properties of charge carrier migration as an electronic process are profoundly related to molecular order as well as molecular motions in mesophase.