Optical-field-induced Freedericksz transition of a nematic liquid crystal doped with diazophenyl

4[4 '-(phenylazo)phenylazo]phenol was synthesized and characterized. Optica l-induced Freedericksz transition of 5CB liquid crystal doped with trace di azophenyl was studied. It was observed that the doped 5CB dramatically decr eased the optical field threshold, and the Freedericksz transition threshol d occurred at optical intensity level of 0.3 mW/mm(2) for the 12.5 mum thic kness planar alignment doped 5CB, which is three orders of magnitude lower than that for the pure 5CB, This new phenomenon indicated that trans-cis is omerization of diazophenyl plays an important role in the decrease of the F reedericksz transition threshold.