Unexpected influences of solvents on excited state properties of solute molecules

Abstract New results are provided which reveal that the anomalous fluorescence of 4,N,N-dimethylaminobenzonitrile and related compounds is emitted by solute-solvent exciplexes. The formation of these exciplexes is not restricted to polar solvent molecules and there is no restriction imposed by the orientation of the amino group relative to the phenyl ring. The triplet state yield is enhanced in all cases by the formation of exciplexes primarily due to a reduction in the radiative rate constant of the singlet state exciplex relative to that of the S 1 state of the unperturbed solute. Exciplexes with H 2 O or D 2 O show a marked isotope effect on their rates for radiationless decay.