A stark spectroscopic study of N(3)-methyl, N(10)-isobutyl-7,8-dimethylisoalloxazine in nonpolar low-temperature glasses:: Experiment and comparison with calculations

Flavins have unique electronic properties that have led to their utilization in biological redox chemistry. Despite this there is relatively little experimental information about such basic electronic properties as dipole moments and polarizabilities for these molecules. We have explored the electronic structure of the ground and first two excited electronic states of an oxidized flavin in nonpolar organic glasses using Stark spectroscopy. The dipole moment change for the S-0 --> S-1 transition is about 3 times smaller than the dipole moment change for the S-0 --> S-2 transition. Dipole moment directions for these excited states have been calculated using the experimental results along with predictions from calculations. The experimental results are consistent with computational predictions of intramolecular charge transfer for the S-0 --> S-2 transition. In addition, we have verified that there is a large change in polarizability for the S-2 state vs the S-0 and S-1 states. Both excited-state polarizability changes show a slight dependence on the polarity of the solvent. The physical origin behind this trend is explored.