Highly sensitive and selective Pd2+ sensor of naphthalimide derivative based on complexation with alkynes and thio-heterocycle

A new fluorescent Pd2+ sensor 1, N-butyl-4-(p-methyloxy)-phenylethynyl-5-thiophenemethylamino-1,8-naphthalimide, was designed and synthesized. It showed highly selective on-off fluorescence changes for Pd2+ among the representative transition and heavy metallic cations, and its fluorescence was efficiently quenched by 5 equivalents of Pd2+ in buffer solution. The sensor also displayed a selective chromogenic behavior toward Pd2+ from yellow to black-red, which could be easily observed by the naked eye.