Investigation of photoinduced electron transfer of the model vitamin E-duroquinone system by means of femtosecond spectroscopy

Photoinduced electron transfer (ET) of the model vitamin E-duroquinone system (MVE-D) has been investigated by means of femtosecond spectroscopy. The interaction between the vitamin E and duroquinone moieties is not extensive in the ground state, and the charge-transfer band is not clearly seen in the absorption spectrum. The bonding of vitamin E to duroquinone largely reduces the lifetime of the lowest excited singlet state (SI state) of duroquinone owing to ET from the vitamin E moiety to the duroquinone moiety. Since the S-1 state [(n,pi*) state] of duroquinone is regarded as a model for the peroxyl radical, the reduction of the lifetime is direct microscopic observation of the initial stage in the corresponding part of the antioxidant process of vitamin E. It is considered that the photoinduced ET of MVE-D corresponds to the inverted regime. The vibrational modes of the product reduce the lifetime by opening ET vibronic channels which have small barriers.