The appearance of reorganization of intramolecular low-frequency modes in the kinetics of electron transfer from the second excited state in zinc-porphyrin derivatives

An analysis of theoretical modeling results of ultrafast kinetics of photoinduced intramolecular charge separation from the second excited singlet state in the dyad Zn-tetraphenylporphyrin-aminonaphthalenediimide (Zn-TPP-ANDI) in a solution of toluene is presented. The calculations are performed within the framework of the stochastic multi-channel model, which includes four electron states (the ground, first and second excited singlet states, the state with charge separation), as well as their vibration sublevels corresponding to the excitation of highfrequency intramolecular vibration modes. A bimodal kinetic curve of population of the state with charge separation observed in experiments is quantitatively reproduced. The absolute yield values of the state with charge separation are determined. The results of the modeling show that intramolecular modes make a significant contribution to the reorganization of low-frequency modes. Quantum chemical calculations were performed, determining the degrees of freedom related to the intramolecular slow motion of nuclei of high amplitude in the dyad Zn-TPPANDI on going from the ground state to the state with charge separation.