Resonance Raman spectroscopy and density functional theory calculation study of photodecay dynamics of tetra(4-carboxyphenyl) porphyrin

Abstract

The 397.9 nm, 416.0 nm and 435.7 nm resonance Raman spectra were acquired for meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP) in tetrahydrofuran solution, and the Raman effect of relaxation dynamics was analyzed according to Herzberg–Teller (vibronic coupling) contributions. Density functional calculations were done to help the elucidation of the Soret (B_x and B_y-band) electronic transitions and the corresponding photo relaxation dynamics of TCPP. The spectra indicate that the Franck–Condon region photo relaxation dynamics upon S₀ → S₄ electronic transition are predominantly along the totally symmetric C_m–ph stretch and Porphin ring breath stretch, and simultaneously along the asymmetric ν(C_m–Phenyl) + δ(N–H) and ν(C_α–C_m–C_α)_as + def (pyr) vibrational relaxation processes. The excited state structural dynamics of TCPP determined from the resonance Raman spectra show that the internal conversion between the B_y and B_x electronic states occurs in tens of femtoseconds, and the electronic relaxation dynamics were firstly interpreted taking into account the time-dependent wave packet theory and Herzberg–Teller (vibronic coupling) contributions.