Selective Fluorescence Turn-On Sensing of Phosphate Anion in Water by Tetraphenylethylene Dimethylformamidine

A tetraphenylethylene (TPE) derivative bearing two dimethylformamidine units was synthesized. The dihydrogen chloride salt of this TPE derivative was soluble in water and showed almost no emission. By addition of phosphate anions, the dihydrogen chloride salt could be transformed into the monohydrogen chloride salt, which was barely soluble and emitted strong fluorescence through aggregation-induced emission (AIE), while many other anions could not bring about a fluorescence enhancement. Meanwhile, the dihydrogen chloride salt and monohydrogen chloride salt could be reversible transformed by addition of acid and base alternately in the presence of phosphate anion, which led to fluorescence turn-on and turn-off. Therefore, the TPE dimethylformamidine holds potential for selectively sensing phosphate anions in water and use as fluorescence pH switch. This study provided a new approach to AIEgen sensors by using formamidine groups.