Unexpected fluorescent behavior of a new pH chemosensor based upon bis-4-piperidine-1,8-naphthalimide linked by the diethylenetriamine

A new fluorescent chemosensor 3 based upon bis-4-piperidine-1,8-naphthalimide linked by the diethylenetriamine was synthesized, and its fluorescent properties were also investigated. Different from other bis-1,8-naphthalimides, no changes in the fluorescence spectra of 3 in the presence of metal cations was observed, and it displayed an unexpectedly strong fluorescence quench in weakly acidic aqueous solutions. Its pKa value (7.25) indicated that it would be suited as a new pH fluorescent chemosensor to monitor changes at the physiological pH range.