2-[Bis(pentafluorophenyl)boryl]-4'-(dimethylamino)azobenzene was synthesized as a hybrid of the intensely fluorescent 2-borylazobenzene and the pH-responsive 4-(dimethylamino)-azobenzene. Quenching and recovery of fluorescence of this azobenzene were reversibly performed by addition of trifluoroacetic acid and triethylamine, respectively. The reason of fluorescence quenching was investigated by theoretical calculations.