Excited state structural dynamics of tetra(4-aminophenyl)porphine in the condensed phase: resonance Raman spectroscopy and density functional theory calculation study.

Resonance Raman spectra (RRs) of tetra(4-aminophenyl) porphine (TAPP) were obtained, and density functional calculations were done to help the elucidation of the photorelaxation dynamics of Soret (B(x) and B(y) band) and Q(y) electronic transitions. The RRs indicate that the photorelaxation dynamics for the S(0) --> S(3) excited electronic state is predominantly along the totally symmetric porphin ring C(beta)=C(beta) + C(m)C(alpha) stretch, C(m)-ph stretch, and simultaneously along the asymmetric nu(C(m)C(alpha))(as) and nu(C(alpha)C(beta))(as) relaxation processes leading to Q(y) while that for S(0) --> S(2) is predominantly along the porphin ring C(beta)=C(beta) + C(m)C(alpha) stretch and simultaneously along the asymmetric nu(C(m)C(alpha))(as) + nu(C(alpha)C(beta))(as) relaxation processes leading to thermal equilibrium in Q(x). The excited state structural dynamics of TAPP determined from RRs shows that internal conversion B(x) --> Q(y) electronic relaxation occurs in tens of femtoseconds and the short-time dynamics were first interpreted with account of the time-dependent wave packet theory and Herzberg-Teller contributions.