Cu(ii) complex-based fluorescence chemosensor for cyanide in aqueous media

Abstract

A fluorescent quinazoline derivative, 6-(2,4-dihydroxyphenyl)-5,6-dihydrobenzoimidazo[1,2-c]quinazoline (H₂L), was designed and synthesized. Its fluorescence could be quenched by the addition of Cu²⁺ in an aqueous media. The binding constant for Cu²⁺ and H₂L was determined to be 9.56 × 10³ M⁻² in DMSO/H₂O (1 : 1, v/v). The crystal structure of the Cu(II) complex, [Cu(HL¹)(Ac)] (1) (H₂L¹ = 4-{[2-(1H-benzimidazol-2-yl)-phenylimino]-methyl}-benzene-1,3-diol, Ac = acetate), revealed that Schiff base complex 1, H₂L¹, was formed in the response system of H₂L to Cu²⁺ via Cu²⁺-assisted C–N bond breakage of the quinazoline ring in H₂L. Consequently, complex 1 was used as a turn-on fluorescence chemosensor for the direct detection of CN⁻, and showed a high selectivity to CN⁻ over a number of anions in the aqueous media, where CN⁻ replaces HL¹ in 1 to form [Cu(CN)_x]^2−x with HL¹ then released and the fluorescence recovered. The detection limit for CN⁻ was 4.0 × 10⁻⁶ M. The cell images showed that 1 could be used to detect intracellular CN⁻.