Lightening flavin by amination for fluorescent sensing†

Abstract

Monitoring of reactive oxygen species (ROS), such as O₂˙⁻, etc., in organisms is of great significance, not only for their essential role in biological processes, but their excessive production may also result in many diseases. Flavin (FL) is a fluorophore that naturally exists in flavoenzymes, and its fluorescent emission (FE) becomes negligible when reduced. This enables the application of FL derivatives as fluorescent sensors for ROS. We presented a theoretical investigation to address the impact of amino substitution on the photophysical properties of aminoflavins (AmFLs). Resulting from the interplay of electronic and positional effects, amination at C8 enhances the electronic coupling between the ground state and the first singlet excited state by enlarging the adiabatic energy change of the electronic transitions and the emission transition dipole moments, weakens the vibronic coupling by decreasing the contribution of isoalloxazine to the frontier molecular orbitals, redshifts the absorption band, and enhances the fluorescent emission drastically in 8AmFL. The theoretically estimated fluorescent emission intensity of 8AmFL is ∼40 times that of FL, suggesting its potential application as a fluorescent sensor.