COMPLEXES OF METHYL 4-(N,N-DIMETHYLAMINO)BENZOATE - SPECTROSCOPY AND DYNAMICS OF THE CHARGE-TRANSFER STATE

The excited states of methyl 4-(N,N-dimethylamino)benzoate isolated in a free jet expansion and complexed with polar, aprotic solvents were studied using mass-resolved, two-color resonance-enhanced multiphoton ionization and picosecond fluorescence emission spectroscopy. In the isolated molecule, the excited electronic state observed is the (1)L(b) State rather than the energetically more stable (1)L(a), state. The large influence of solvent-induced nonadiabatic interactions on the twisted intramolecular charge transfer process is manifested in the study of methyl 4-(N,N-dimethylamino)benzoate complexes with polar, aprotic solvents. Large red shifts are observed in REMPI spectra of the methyl 4-(N,N-dimethylamino)benzoate complexes, with the extent of the shift proportional to the dipole moment of the solvent. Besides normal Stokes-shifted emission in the fluorescence spectra of the complexes, a second emission band is observed at much lower energies than the excited energy. This band is assigned to the charge transfer state, which is observed because of solvent-induced nonadiabatic interactions.