Study On Fluorescent Probes With Multi1,8-Naphthalimide Fluorophores For Heavy Metal Ions

Three novel fluorescent probes (named as NET, NETDE and TMNET) with multi fluorophores and receptors for Fe3+and Cr3+were designed and synthesized through1,8-naphthalimide and N,N-dimethylethylenediamine grouped by tris(2-aminoethyl)amine and cyanuric chloride. Their structures were characterized by FT-IR, LC-MS, NMR and elementary analysis. Their photophysical properties in different solvents, their sensing activity and mechanism for Fe3+and Cr3+, as well as the effects of the solvents and the pH value on their sensing behaviors were investigated.NET absorbed in the UV region (270～400nm) with the molar extinction coefficient of (1.10～3.57)×104L·mol-1·cm-1and emitted relative weak fluorescence (340～470nm) with the fluorescent quantum yield of0.0120～0.0269. Owing to the presence of the alkylamino group at the C-4position of the1,8-naphthalimide unit, the absorption and emission spectra of NETDE and TMNET bathochromically shifted to the visible region and the fluorescence was greatly enhanced.After examining their selectivity to metal ions in different solvents, the optimized detection media for NET, NETDE and TMNET were determined as DMF/H2O,2:3(v/v),4:1(v/v) and9:1(v/v) respectively, in which NET and TMNET were "turn-on" Fe3+fluorescent probes, while NETDE was a "turn-on" Fe3+and Cr3+fluorescent probe. The selectivity and sensitivity of NET, NETDE and TMNET were far better than that of the structurally similar controls with one fluorophore and one receptor, one fluorophore and two receptors, two fluorophores and three receptors, and the1,8-naphthalimide-functionalized dendritic analogies.NET bound Fe3+with a1:1stoichiometry by the N atoms from the central tertiary amine and the imide moiety. NETDE chelated Fe3+with a1:2stoichiometry by the N atoms from the central tertiary amine, the imide moiety, and one of the three (((N, N-dimethyl)amino)ethyl)amino groups, while a1:1complex was formed between NETDE and Cr3+by the contribution of the N atoms from the peripheral(((N,N-dimethyl)amino)ethyl)amino groups. Differently, a complicated complex was formed between TMNET and Fe3+by the N binding sites from the (((N,N-dimethyl)amino) ethyl)amino groups on the periphery of TMNET.The working pH ranges for NET, NETDE and TMNET were3.1～6.4,5.5～7.5and3.5～8.5, respectively. The response of NET, NETDE and TMNET to Fe3+and Cr3+were quick and stable, and the probes could be applied in environmental and biological systems.