Ultrafast refractive index change induced by photoisomerization of an azobenzene derivative: contribution of solvation dynamics of solvent molecules

The refractive index change induced by the photoisomerization of trans-4-aminoazobenzene in alcohol solutions was investigated by using the ultrafast transient lens (UTL) method. We observed a decrease of the refractive index of the solution, which consisted of three decay components with time constants of 0.3, 0.7 and 2 ps. The amplitude of the 0.3 ps-decay component of the UTL signal was rather larger in ethanol than in heptanol, while such solvent-dependence was not detected in the transient absorption measurements. We considered that the difference of the UTL signal in two solutions originated from solvation dynamics of solvent molecules.