Investigation of photoinduced electron transfer in model system of vitamin E-duroquinone by time-dependent density functional theory

摘要

Photoinduced electron transfer of the model system composed of vitamin E and duroquinone has been investigated using time-dependent density functional theory.Calculations for the excited states tell that the photoexcitation of the model system can directly yield the charge transfer states in which the vitamin E moiety is positively charged but the duroquinone moiety is negatively charged.Our theoretical investigations indicate that the second charge transfer state of the model system can also be produced through the decay of higher locally excited state S_4.Since S_4 state in the model system corresponds to S_1 state of the isolated duroquinone used as a model for peroxyl radical,and S_2 state has the character of electron transfer from the tertiary amine group of the vitamin E moiety to the duroquinone moiety,the decay from S_4 to S_2 corresponds to the dynamic process following the photoexcitation of the duroquinone moiety of the model system,i.e.,the initial stage of antioxidant reaction of vitamin E.Calculations of the kinetic parameters for the electron transfer have been carried out in the framework of the Marcus-Jortner-Levich formalism.Our calculations confirm that the electron transfer from S_4 to S_2 possesses the character of the inverted regime and the barrier is negligibly small.