Optical spectroscopy of isolated flavins: photodissociation of protonated lumichrome

This research paper investigates the optical properties of flavins, which are influenced by e.g. charge, oxidation states, and environmental conditions. The study specifically examines the electronic spectrum of cold protonated lumichrome, a small flavin molecule, using photodissociation in a cryogenic ion trap tandem mass spectrometer. The observed vibronic spectrum is attributed to the S₁ → S₀ transition of the most stable N5-protonated isomer. Quantum chemical calculations and multidimensional Franck–Condon simulations were employed to interpret the results. The findings reveal a significant red shift in the band origin upon protonation, indicating a change in the electronic structure. The study underscores the importance of understanding the optical properties of flavins in various states, such as oxidation, protonation, and metalation, to gain insights into their roles in biological processes.