Photoinduced disordering dynamics of a cyanobiphenyl liquid crystal containing quinizarin

Photoinduced changes in a liquid crystal (LC) alignment were measured for 4 -octyloxy-4'-cyanobiphenyl containing quinizarin. Kinetic analyses were car ried out for both photoinduced response and thermal relaxation of the LC al ignment in the temperature range from 50 degrees C to 78 degrees C. Thermal relaxation curves of birefringence after termination of Ar+ laser in irrad iation show only one component in the smectic A phase, and two components i n the nematic phase, revealing the microscopic environment of dye molecules in LC solvents. This change does not exactly correspond to the macroscopic phase transition from smectic to nematic, which suggests interaction betwe en LC mesogens and dye molecules due to photoexcitation. An unrecoverable p ortion of birefringence for thermal ordering/relaxation processes after ter mination of photoirradiation was observed in the smectic phase measured in the course of heating process.