Infrared circular dichroism and linear dichroism of liquid crystals

In order to test the validity of our recently reported theory of optical activity near absorption bands of cholesteric liquid crystals, we have measured the infrared linear dichroism (LD) of the nematic liquid crystal p-methoxy-p′-n-butylaxoxybenzene and the circular dichroism (CD) of the cholesteric phase of this liquid crystal obtained by doping with 0.75 mole-% cholesteryl-2-(2-ethoxyethoxy)ethyl carbonate. Using the measured LD data to define the optical properties of the individual layers of the cholesteric structure, we calculate the CD of the cholesteric material by means of our macroscopic theory. The calculated signs, amplitudes, positions, and shapes of the CD bands agree closely with observation. This demonstrates that the CD is quantitatively explained by introducing frequency-dependent complex terms into the spiralling dielectric tensor of the Oseen-de Vries model for cholesteric liquid crystals.