Optical investigation of thin films of liquid-crystalline lutetium bisphthalocyanine

Thin films of bis[4,5,4',5',4",5",4"',5"']-octakis(hexylthiophthalocyanine) of lutetium(III) were prepared by spin coating at different speeds in the range of 2000-6000 rpm. The films undergo phase transition on heat treatment at temperatures above 120 degreesC and the formation of a mesophase. The Q-bands in the visible absorption spectra of the films are broader and become red shifted compared to ones obtained for molecules in chloroform solution. Heat treatment produces molecular ordering, which is believed to be due to the edge-to-edge interaction between neighboring Pc moieties. Reduced film thickness and changes in optical constants are also attributed to thermally induced molecular reorganization corresponding to the liquid crystalline phase. AFM and polarized microscopy images are consistent with the phase transformations. (C) 2004 Kluwer Academic Publishers.