BODIPY blocked anthroxyl radicals: the substituent effect on reactivity and fluorescence turn-on detection of a hydroxyl radical

Two BODIPY-substituted anthroxyl radicals were investigated. The one with two ethyl substituents (2Et-BO-An-O) is sensitive to air and silica gel due to the lack of sufficient kinetic blocking, while another one with four methyl substituents (4Me-BO-An-O) shows high stability. The structure of the latter was fully characterized by X-ray crystallographic analysis and electron-spin resonance spectra. 4Me-BO-An-O was subjected to react with various reactive oxygen/nitrogen species (ROS/RNS) and selective fluorescence turn-on detection of a hydroxyl radical was achieved, validating the concept of "using stable radicals to detect ROS/RNS".