Fourier Transform Infrared Absorption Study of Hexa(hexylthio)triphenylene: A Discotic Liquid Crystal

Abstract

Abstract We have used Fourier transform infrared absorption spectroscopy to study the molecular motions of hexa(hexylthio)triphenylene as a function of temperature. Our measurements show pronounced changes in the CH3 stretching mode frequencies at the K → H transition. (The H phase displays long range incommensurate helical order). However, the CH2 stretching mode frequencies show much less variation with temperature, suggesting that only the ends of the alkyl tails undergo much change in the different phases. The CH bending and benzene stretching vibrations show a change in the frequency-temperature dependence at both the K → H and the H → Dhd transitions. There is no observable change in the spectrum in going from the Dnd to the 1 phase. We also present detailed syntheses for hexa(hexyl-thio)triphenylene and its C5 and C7 homologs. Physics Abstracts Classification: 64.70.M, 61.30.E, 33.20.E, 78.30.