A versatile fluorescent dye based on naphthalimide: Highly selective detection of Hg²⁺ in aqueous solution and living cells and its aggregation-induced emission behaviour

A simple and versatile fluorescent dye NPS based on 1,8-naphthalimide was successfully designed and prepared. It was found that NPS exhibited excellent selectivity for Hg²⁺ over many other metal ions including Zn²⁺, Mn²⁺, Ba²⁺, Ni²⁺, Cu²⁺, Co²⁺, Pb²⁺, Mg²⁺, Cd²⁺, Fe²⁺, Al³⁺, Ag⁺, Na⁺, and Li⁺. In particular, NPS displayed a significant fluorescence "turn-on" to Hg²⁺ in aqueous solution and living cells, which could be potentially used for quantification of Hg²⁺. Moreover, two model compounds were rationally designed and synthesized, from which further insight into the sensing mechanism and binding mode of NPS with Hg²⁺ was obtained. Surprisingly, NPS exhibited interesting twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) behaviours in aqueous solution.