Theory of Rotatory Dispersion of Cholesteric Liquid Crystals

Abstract

A theory is developed of the circular dichroism and rotatory power of thin films of cholesteric liquid crystals. It is an extension of the treatment for infinitely thick specimens discussed in a previous paper. The therory predicts that the circular dichroism of a thin film plotted as a function of wave-length should exhibit a principal maximum accompanied by subsidiary maxima, and that the rotatory dispersin should be anomalous. Experimental circular dichroism and rotatory dispersion curves are presented for cholesteric cinnamate, cholesteryl-2-propyn-1-yl carbonate and spectratherm. The results are in qualitative agreement with the theory both inside and outside the region of reflexion. The rotatory dispersion curves are also in accord with the de Vries equation outside the region of reflexion.