The optical reorientation of nematic liquid crystals doped with azo dyes is studied. It is shown that in the presence of absorption both the trans and cis isomers enhance significantly the optical torque; they contribute, however, with opposite signs to the net enhancement and tend to cancel each other’s effect. The anomalous angular dependence of optical reorientation reported by Zolotko et al. is explained by considering the photoinduced trans-cis equilibrium.

• Received 21 April 1998

DOI:https://doi.org/10.1103/PhysRevE.58.4598