A dual response fluorescent sensor for HNO and S2− ions using a Cu(ii) complex based probe assisted by detailed DFT studies

Abstract

A Cu(II) based sensor (1) prepared by the complexation between (quinolin-8-ylamino)-acetic acid hydrazide (L²) and Cu²⁺ ions has been developed for a highly sensitive and selective recognition of HNO and S²⁻ over other biologically abundant anions with prominent enhancement in absorption and emission intensities. The sensor (1) shows weak fluorescence due to ET (electron transfer) but upon addition of HNO and S²⁻ a large enhancement in the fluorescence intensity (F.I.) was observed over other possible competitive anions on the basis of reduction of Cu(II) to Cu(I) and formation of CuS, respectively. The 1 : 1 complexation was characterized by mass spectrometry (MS), elemental analysis and Job's plot. The corresponding K_f value was evaluated to be (4.934 ± 0.05) × 10⁴ M⁻¹ for Cu²⁺ from UV-Vis absorption titration. Quantum yields of L² and [Cu-L² + S²⁻] and [Cu-L² + HNO] complexes in acetonitrile (CH₃CN) are found to be 0.107, 0.09 and 0.07, respectively, using quinine sulphate as the standard.