Spectroscopic monitoring of thermally induced molecular reorganisations within spin-coated and Langmuir–Blodgett films of mesogenic phthalocyanines

Abstract

Examples of mesogenic 1,4,8,11,15,18,22,25-octaalkylphthalocyanines and their zinc analogues, series 1, have been deposited as spin-coated films onto glass slides. Thermally induced molecular reorganisations within the films have been investigated by optical spectroscopy. Temperatures of transitions observed in the films correspond well with those for the liquid-crystal phases of the samples as bulk materials. The response of spin-coated films and LangmuirBlodgett films of a series of mesogenic 1,4,8,11,15, 18-hexaalkyl-22,25-bis(4-hydroxybutyl)phthalocyanines towards heat has also been studied. The spin-coated films generally undergo molecular reorganisation at temperatures corresponding to the phase transitions in the bulk material, though over a slightly wider temperature range than was observed for the films of series 1. The LB films behave rather differently. There is a gradual modification in film structure as the material approaches the melting temperature but there appear to be no intermediate transitions. The melting temperatures are close to those of the bulk material for monotropic liquid crystals but lower for enantiotropic materials.