External electric field effects on absorption, fluorescence and phosphorescence spectra of 4-(dimethylamino)benzonitrile in a polymer film

Electric-field-induced changes in the absorption, fluorescence, and phosphorescence spectra of 4-(dimethyl-amino)benzonitrile (DMABN) doped in a polymer film were measured, and the electric dipole moment and molecular polarizability in the locally excited (LE) and charge transfer (CT) singlet states as well as in the phosphorescent triplet state were evaluated. Time-resolved fluorescence measurements both in the absence and in the presence of electric fields were also carried out. A field-induced change in the quantum yield of the LE and CT fluorescence as well as of the phosphorescence is found and the charge transfer from the LE to the CT state is shown to be accelerated by an electric field, resulting in the field-induced decrease in the population ratio of the LE relative to the CT state. The dipole moment of the phosphorescent triplet state is found to be smaller than that of the LE state, with a value similar to that of the ground state.