Vibrationally resolved absorption and fluorescence spectra of flavins: A theoretical simulation in the gas phase.

Flavin is involved in a wide range of life processes. Flavin can exist in different forms due to its ability to transfer electron(s) in different physiological conditions. It is difficult to experimentally obtain the absorption and fluorescence spectra at the vibrational level. A systematically theoretical simulation is a necessary way to explore the fine structure of these spectra of all forms of flavin molecules. In this study, the vibrationally resolved absorption spectra and fluorescence spectra of five forms of flavins (fully oxidized form FLox, neutral radical form HFLsq∙, anionic radical form FLsq−∙, neutral reduced form H2FLred, and anionic reduced form HFLred−) are simulated by adiabatic or vertical methods combined with time‐dependent or time‐independent (TD/TI) formalisms, with displace, Duschinsky, and Herzberg−Teller (HT) effects under the framework of the Franck‐Condon approximation. The statistical vibronic transition analysis reveals the unity of the spectrum transition property, the relevant normal modes, and the primary geometrical variations. The correlation between geometry and spectral calculation is explained. [ABSTRACT FROM AUTHOR]