A BODIPY-based 'turn-on' fluorescent probe for hypoxic cell imaging

A boron-dipyrromethene (BODIPY) dye containing a styryl substituent with a hydroxyl and nitro group, 1a, exhibits a 'turn-on' fluorescence response for hypoxic cells. The presence of the electron-withdrawing nitro group results in a highly efficient nonradiative decay of the S1 state, and hence a recovery of fluorescence intensity when nitro reduction occurs under hypoxic conditions.