Journal of Physical Chemistry, Vol.98, No.40, 9955-9959, 1994
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 fluorescence spectra using first-order configuration interaction methods. Optimized geometries were calculated for the ground and first excited singlet and triplet state of both neutral and anion molecules. Solvatochromic 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 absorption 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 be different. Experimental observation that anion formation strongly deactivates fluorescence is related to these differences. Coupling of the first excited singlet to its cognate triplet state is suggested as the quenching mechanism in the anion, and the same process occurs more weakly in the neutral species.