Ultrafast Excited State Deactivation of Triphenylmethane Dyes

We have carried out ultrafast pump−probe measurement of four TPM dyes, malachite green (MG), brilliant green (BG), crystal violet (CV), and ethyl violet (EV), with a time resolution of 30 fs. The pump−probe signal showed that solvent dependence arose first in the femtosecond time regime, e.g., the decay of n-butanol solution was clearly slower than the methanol solution just 50 fs after the initial photoexcitation. The signal decays in a multiexponential manner and the slower components showed stronger linear dependence on the solvent viscosity than did the faster components. We have also carried out temperature-dependent measurement of ethanol solution and calculated the activation energies from the Arrhenius plots of each components. The activation energies and effective volumes were larger for slower decays. The activation energy of the viscosity of ethanol was larger than that of the decay components of TPM dyes. These observations are explained with a combined effect of microviscosity and intramolecu...