Time-resolved excited state dynamics of a cyanine dye

The photophysics and isomerization dynamics in the excited state of a cyanine dye, 3,3′-di(3-sulfopropyl)-thiacyanine triethylaminium salt was investigated. Using the femotosecond time-resolved fluorescence up-conversion technique, wavelength-dependent fluorescence dynamics was observed and the theoretical prediction of the dual fluorescence behavior was vindicated. The results were explained using a barrierless isomerization reaction model. The origins of two decay components were assigned to the relaxation within the excited state and the S1→S0 transition, respectively, and the time constants were obtained.