ELECTRONIC-STRUCTURE OF THE EXCITED-STATES AND PHENOL FLUORESCENCE

The excitation energies of phenol and the deprotonated anion have been determined at geometries relevant to both the absorption and fluoresc ence spectra using first-order configuration interaction methods. Opti mized geometries were calculated for the ground and first excited sing let and triplet state of both neutral and anion molecules. Solvatochro mic shifts are predicted to be very small since the ground and singlet excited state dipole moments are very similar. The fluorescent shift is dominated by the differences in the vertical transition energies at the equilibrium geometries of the ground and excited state. Anion abs orption and fluorescence shifts are substantially to the red of those found for the neutral molecule. Ordering and assignment of the tripler valence states of neutral and deprotonated phenol are determined to b e different. Experimental observation that anion formation strongly de activates fluorescence is related to these differences. Coupling of th e first excited singlet to its cognate triplet state is suggested as t he quenching mechanism in the anion, and the same process occurs more weakly in the neutral species.