Solvent dependent ultrafast ground state recovery dynamics of triphenylmethane dyes

We have studied ground state recovery dynamics of triphenylmethane dyes, br illiant green and malachite green, by a single wavelength pump-probe spectr oscopy at 635 nm with a time-resolution of 33 fs. The recovery of the groun d state dependeded on solvent viscosity and also on solute molecular size. We observed a plateau or a rise component in the signal which indicates an intermediate state. The rise time also showed solvent viscosity dependence even in the ultrafast time domain, although no solute dependence was observ ed. It is suggested that the lack of solute dependece indicates that only s mall conformational change is involved in the initial process.