Photo-uncaging of reactive species and fluorescence with visible and NIR light

Abstract

In recent years, diazo compounds has emerged as one of the most versatile functional groups in the field of chemical biology. 4-Diazomethyl-coumarin was previously reported to exhibit excellent stability and utility. Here we report that a diazomethyl coumarin can be photo-uncaged to generate a reactive carbene, which subsequently undergoes bond insertion. Unlike ordinary diazo compounds that require UV irradiation, the coumarin-fused diazo group utilizes 400 nm light for uncaging. Trifluoromethylation considerably improves the yield by stabilization of the carbene intermediate. While the fluorescence emission is efficiently quenched by the diazo group, significant fluorescence enhancement is observed after photo-activation. Two-photon photolysis with 800 nm laser can also be accomplished. We envision that this diazo compound can be applied as a new UV-free fluorogenic photoaffinity labeling reagent that are compatible with in situ (live cells) studies to capture endogenous bio-molecular interactions.