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 (S1 state) of
duroquinone owing to ET from the vitamin E moiety to the duroquinone
moiety. Since the S1 state [(n,π*)
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.