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 Pd ²⁺ among the representative transition and heavy metallic cations, and its fluorescence was efficiently quenched by 5 equivalents of Pd ²⁺ 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.