A dual-responsive Dansyl–Naphthalimide system for Hg(II) CHEF detection and ligand-mediated Cu(II) reduction with catalytic relevance

Abstract

We report a compelling structure–property relationship in a series of four naphthalimide-derived ligands, engineered for the selective and differential detection of Hg(II) and Cu(II) ions. By integrating a dansyl moiety, we induce intramolecular electron transfer that gives rise to two non-redox-innocent dyad systems. Notably, the detection of Hg(II) operates through a rare chelation-enhanced fluorescence (CHEF) mechanism, an unusual pathway considering the heavy atom effect typically associated with mercury. In contrast, the Cu(II) dyads reveal striking reduction of Cu(II) to Cu(I) in solution, driven by ligand-to-metal electron transfer, as conclusively demonstrated via EPR and XPS analysis. Furthermore, introducing a catalytic substrate probe highlights that this redox transformation is the bottleneck in catalytic efficiency. These findings provide deep mechanistic insights and position these ligands as versatile platforms for dual-mode ion sensing and redox-responsive catalysis.