Transient resonance Raman spectrum of meso-tetraphenylporphine: an analysis of chemical factors that influence the dynamics of the excited triplet states of metalloporphyrins

We report the resonance Raman spectrum of the first excited singlet (S1) and triplet (T1) states of meso-tetraphenylporphine. The structure of the T1 state is characterized by a weakening of the C(beta)C(beta) bonds and a strengthening of the C(alpha)N bonds relative to the ground electronic state. These changes are of considerably lower amplitude than those observed for zinc(II) tetraphenylporphyrin, where Jahn-Teller instability of the T1 state was observed (Walters, V. A.; de Paula, J. C.; Babcock, G. T.; Leroi, G. E. J. Am. Chem. Soc. 1989,111, 8300). By comparing data on a number of compounds, we provide a preliminary analysis of the chemical factors that modulate the dynamics of the excited states of porphyrins.