Biomimetic Design of Naphthalene Diimide Derivatives for Highly Selective Mercury Ion Fluorescence Detection

ABSTRACT

In this study, we present an approach to the selective detection of mercury (Hg ²⁺ ) using organic fluorophores, guided by biomimetic design principles. Conventional approaches predominantly employ sulfur‐containing functionalities, which, although effective, often suffer from cross‐reactivity with competing metal ions such as As ³⁺ , Pb ²⁺ , and Cu ²⁺ . Here, oxygen‐ and nitrogen‐based functional groups are incorporated with naphthalene diimide (NDI) derivatives, inspired by biological coordination environments, to enhance selectivity. NDI derivatives, including NDI‐A, NDI‐A*, and NDI‐Cys*, are synthesized with strategically positioned hydroxyl and carboxylate moieties to modulate metal‐ligand interactions. Among the prepared compounds, the NDI‐A* derivative exhibits improved selectivity toward Hg ²⁺ over fifteen potential interfering ions and demonstrates suitability for real‐sample analysis. The sensing performance is further evaluated by fluorescence spectroscopy and density functional theory (DFT) calculations. DFT studies provide mechanistic insights, which reveal favourable binding energies and a ligand‐to‐metal charge‐transfer (LMCT) pathway governing fluorescence quenching. The NDI‐A* derivative‐based sensor achieves a limit of detection of ^∼ 42 ppb and a limit of quantification of ∼141 ppb, with a linear detection range spanning 42–1330 ppb for selective Hg ²⁺ detection.