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 applied to the study of the excited-state dynamics of an analogue of crystal violet with julolidino-substituted phenyl rings in ethanol, propanol, and butanol at room temperature. Experiments were also carried out with crystal violet for comparison. The time-resolved spectra are interpreted by a barrierless adiabatic photoreaction, leading to the formation of a dark transient excited state involving the torsion of one of the substituted phenyl rings connected with the charge shift from the nitrogen of the amino substituent to the central carbon of the triphenylmethane structure. The effects of solvent viscosity, size, and electron donor-acceptor character of the substituted phenyl rings on the transient kinetics are examined. The relaxation of the transient excited state back to the equilibrium ground state is shown to be sensitive to the solvent viscosity but less than its formation reaction. 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.