Synthesis of mono-(p-dimethylamino)styryl-containing BOPHY dye for a turn-on pH sensor

Mono-substitutional bis(difluoroboron)1,2-bis((1H-pyrrol-2-yl)methylene)hydrazine (BOPHY) 3a with a (p-dimethylamino) styryl group in the a-position was confirmed to be synthesized by the Knoevenageltype condensation. Dimethylamino-containing BOPHY dye 3a is almost non-fluorescent by the ICT effect. Upon the protonation of the tertiary amine function of 3a, the strong fluorescence (Phi(f) = 0.98) was released and the fluorescence intensity was dramatically increased by one thousand fold. BOPHY 3a can be used as a pH probe.