ORIENTATIONAL RELAXATION OF AMINOCOUMARINS BY TIME-RESOLVED DICHROISMWITH PICOSECOND PULSES

The orientational relaxation times (tau(r)) of coumarin 102 and coumar in 138 molecules were measured in ethanol and ethylene glycol solution s at room temperature by transient dichroism technique on picosecond t ime scales. The experimental data were compared with the calculated va lues based on Stokes-Einstein-Debye (SED) hydrodynamic model. The resu lts show that the measured values of tau(r) of both the dyes in ethano l reasonally agree with the theoretical ones; but for ethylene glycol solutions, relaxation times are shortened indicating the inadequacy of the SED model for the description of the rotational motions. The resu lts are discussed on the basis of molecular structures of the dyes and intermolecular interactions.