Excited state dynamics of a julolidino analogue of crystal violet: A relaxation path through a conical intersection?

Transient absorption spectroscopy with subpicosecond time resolution was ap plied to the study of the excited-state dynamics of an analogue of crystal violet with julolidino-substituted phenyl rings in ethanol, propanol, and b utanol at room temperature. Experiments were also carried out with crystal violet for comparison. The time-resolved spectra are interpreted by a barri erless adiabatic photoreaction, leading to the formation of a dark transien t excited state involving the torsion of one of the substituted phenyl ring s connected with the charge shift from the nitrogen of the amino substituen t to the central carbon of the triphenylmethane structure. The effects of s olvent viscosity, size, and electron donor-acceptor character of the substi tuted phenyl rings on the transient kinetics are examined. The relaxation o f the transient excited state back to the equilibrium ground state is shown to be sensitive to the solvent viscosity but less than its formation react ion. A relaxation model via a conical intersection between the S-1 and S-0 potential surfaces, involving torsional motion of two of the phenyl rings, is postulated for the back charge-shift reaction.