Molecular Luminescence Studies of Flavins. I. the Excited States of Flavins

The lowest excited singlet and triplet states of flavins have been investigated by means of luminescence polarization (photoselection) and P–P–P SCF–MO Cl methods. The fluorescent and phosphorescent states of flavins of varying structures such as isoalloxazines (e.g., riboflavin), alloxazines (e.g., lumichrome), and lumazines (e.g., 6,7,8-trimethyllumazine) have been assigned (π,π∗) symmetry. However, the (n,π∗) states have been found to play a significant role in the luminescence processes of flavins, particularly of alloxazines. Attempts have been made to characterize various electronic transitions of flavins in the visible and near-uv regions of the absorption spectra, and to reconcile diverse spectroscopic data reported in the literature.