Molecular structure, spectroscopic and photophysical data for the singlet state of 3-benzyl-lumiflavin in different solvents are presented. Theoretical studies concerning singlet-singlet and triplet-triplet excitation energies were carried out using time-dependent density functional theory (TD-DFT) calculations. These predictions are in good agreement with the experimental results, which reflect the solvent interactions. All the observable singlet-singlet transitions have π-π* character. The title compound appears to be an efficient sensitizer of the production of singlet oxygen (φΔ = 0.53). The crystal structure of 3-benzyl-lumiflavin is also presented, along with its solid-state photophysical data. © The Royal Society of Chemistry and Owner Societies 2005.