Journal of Physical Chemistry, Vol.100, No.21, 8628-8632, 1996
Picosecond Polarization Grating Study of the Effect of Excess Excitation-Energy on the Rotational-Dynamics of Rhodamine 6G in Different Electronic States
The effect of excess excitation energy on the rotational dynamics of rhodamine 6G in the ground and the first singlet excited state has been investigated in series of n-alcohols and alkanenitriles using the picosecond polarization grating technique. In nitriles. the reorientation times are the same for excitation at the S-1 <-- S-0 and S-2 <-- S-0 transitions, and no state dependence could be detected. in alcohols, the rotational dynamics of rhodamine 6G in the excited state is about 25% faster when formed with 1.15 eV excess excitation energy. This effect is ascribed to a decrease of the hydrodynamic volume due to dissociation of solute/solvent hydrogen bond following intramolecular vibrational redistribution. An accompanying perturbation of the solvent shell structure caused by thr fast local temperature jump is not excluded.