SAC-CI theoretical study on the excited states of lumiflavin: Structure, excitation spectrum, and solvation effect

The excited states of a flavin-related compound, lumiflavin, were studied by the symmetry-adapted cluster (SAC)-configuration interaction (CI) method. The absorption peaks observed in the experimental spectrum were theoretically assigned. Transition energy of some low-lying n–π* states were obtained. The energy minimum structures of the first singlet and triplet excited states were calculated by the SAC-CI method. The structural changes upon excitation were at most 0.05 Å. The solvation effect on the absorption energy in aqueous solution was investigated using polarizable continuum model (PCM) and by including water molecules into the computational model. The solvatochromic shift of the second peak (31A′ state) originates from both microscopic (hydrogen bonding) and macroscopic (electronic polarization of solvent) solvation effects.