New blue fluorescent sensors for metal cations and protons based on 1,8-naphthalimide

Monomeric 1,8-naphthalimide in acetonitrile was found to respond to the presence of metal cations (Zn2+, Pb2+, Cu2+ and Fe3+) via enhancement of its fluorescence intensity; in the nonpolar solvent, tetrahydrofuran, the response was negligible, regardless of the nature of the cations used. When 1,8-naphthalimide was copolymerised with styrene, the ensuing high Mr polymeric chemosensor reacted selectively to the addition of Fe3+ cations. The finding that the fluorescence intensity of this high Mr sensor increased in acidic media due to protonation of the N,N-dimethylamino receptor groups, suggests that it may offer potential as a reusable sensor for water pollution by Fe3+ cations and protons.