Azoanthracene-core structure as Cu-assisted CO sensing probe: Characterization, performance, and bioimaging.

Detection of endogenous CO (carbon monoxide) is an interesting topic in biology because it has been discovered as a messenger for signal transduction and therapeutic effects in vital biological activities. Fluorescence imaging has proven a powerful tool for detecting endogenous CO, which drives the development of low-cost and easy-to-use fluorescent probes. In this study, four azobenzene derivatives (A1, A2, A3, and A4) with various substituents were reported, including their geometric structures, photophysical parameters, and spectral responses to Cu and CO. The relationship between substituent structure and performance was discussed along with Cu quenching and CO sensing mechanisms. The optimal probe (A1), which had no substituent, efficiently quenched fluorescence in the presence of Cu, with its PLQY decreased from 0.33 to 0.02, PLQY = photoluminescence quantum yield. Upon CO deoxidization, A1's fluorescence could be recovered (PLQY recovered to 0.32) within 180 s. Its sensing mechanism was static by forming a non-fluorescent complex with Cu (with a stoichiometric ratio of 1:1). The bioimaging performance of A1 for endogenous CO in HeLa cells was reported.