Study of photoisomerization of azo dyes in liquid crystals

The trans-cis isomerization of azo dyes in liquid crystalline hosts is studied. It is shown that the full set of parameters governing the isomerization process can be deduced from polarized pump–probe transmission measurements. The results indicate that the dye order parameter for the trans isomer is relatively high and is strongly related to the liquid-crystalline order. The cis isomer exhibits a much lower dye order parameter and is not strongly dependent on the liquid-crystalline phase. The barrier to the thermal cis-trans relaxation is found to be relatively unaffected by the liquid-crystalline phase, while changes are observed in the pre-exponential factor.