Optical Properties of Lyotropic Poly(γ-benzyl L-glutamate) Liquid Crystals

Abstract

To establish methodologies for determining the cholesteric sense of lyotropic poly(y-benzyl L-glutamate) (PBLG) liquid crystals, we have examined various optical activities associated with the cholesteric twist. A colored PBLG film retaining the cholesteric structure is prepared and its pitch-band circular dichroism (CD) and optical rotatory dispersion (ORD) spectra are measured. The established relationship between cholesteric sense and ORD sign is then applied to large-pitch cholesterics in solutions where the sign of liquid crystal induced circular dichroism (LCICD) is determined. The observed LCICD signs are negative for a sidechain phenyl chromophor and positive for a guest achiral dye, acridine orange, in a left-handed PBLG liquid crystal exhibiting a negative optical rotation. We demonstrate that the ORD and LCICD signs in PBLG liquid crystals depend only on the cholesteric sense hence they can be used as simple diagnostics for the sense determination.