Isocyano-functionalized, 1,8-naphthalimide-based chromophore as efficient ratiometric fluorescence probe for Hg2+ in aqueous medium

A type of isocyano-functionalized, 1,8-naphthalimide-based chromophore (M2) was successfully synthesized from its primary amine-derivatived precursor (M1) compound. The chemical structure of M2 was verified by FT-IR, NMR and HRMS analyses. The presence of electron-withdrawing isocyano group brought significant influence to the optical properties of M2. Distinct from the yellowish green emission of its precursor (M1), M2 emitted ultraviolet light (with the emission peak at similar to 389 nm, excited by 352 nm) in THF-water [V-THF/V-water = 3/7, buffered with 5 mM sodium dihydrogen phosphate-disodium hydrogen phosphate (PB), pH = 7.4] co-solvent system. Interestingly, M2 exhibited distinctive and selective optical response (with significant enhancement of emission at 560 nm) toward Hg2+. In Hg2+ titration process, PL spectra of M2 displayed contiguous ratiometric alteration (simultaneous decreasing at 389 nm and increasing at similar to 560 nm). Hg2+-assisted hydration of isocyano group to amino group on M2 was proposed as the plausible probing mechanism in this current case. (C) 2017 Elsevier B.V. All rights reserved.