Experimental Study of the Photoisomerization of Azo Dye in Nematic Liquid Crystal Host

摘要

The photoisomerization of azo dye molecules in two different nematic liquid crystal host is investigated. The absorption coefficients of trans and cis isomers are determined using a pump-probe technique. The absorption coefficients of trans isomers were measured in the absence of the pump beam. Although, the absorption coefficients of the cis isomers were calculated in the presence of the pump beam using the rate equation of cis isomers in the steady state and under saturation condition. The investigation of beams polarization effects indicates dichroism of trans and cis forms of azo dye molecules. Using the experimentally obtained results, the ratio of quantum efficiency of the trans-cis transition to that of the cis-trans transition was calculated. Then results were used to obtain the value of the fraction of cis isomers and also the order parameters of the dye molecules in the host liquid crystal medium.