ZnO-benzimidazole composite for selective detection of Zn²⁺ and Mg²⁺ ions

Ion-sensitive benzimidazole compound L1 was obtained by a reaction between 4-tert-butyl-2,6-diformylphenol and 2-(2-aminophenyl)-1H-benzimidazole. The X-ray crystal structure and 3D Hirschfeld analyses show the importance of the presence of water in the crystal lattice. The L1 compound exhibited luminescence in DMSO (423 nm) and a solid-state (487 nm). DFT calculations of the luminescence spectra suggest green emission from the enol form of L1. The cyclic benzimidazo[1,2-a]quinoline derivative L1 in DMSO solution shows sensory properties towards Zn²⁺ and Mg²⁺ ions in the range of 0.01-14. 65 μM and 0.01-59.43 μM concentrations of Zn²⁺ and Mg²⁺ ions, respectively. To improve the sensitivity of L1 to metal ions, a novel ZnO-benzimidazole composite was obtained by combining L1 and ZnO nanofibers (ZnO_nf). The sensing properties of the ZnO_nf-L1 composite towards Zn²⁺ and Mg²⁺ ions were evaluated using photoluminescence spectroscopy. The ZnO_nf-L1 composite sensitively and efficiently detects Zn²⁺ ions at λ_em = 427 nm (_CZn²⁺ = 0-4 μM) and Mg²⁺ ions at λ_em = 427 nm (_CMg²⁺ = 0-32 μM). The changes in the emission intensity of L1 and ZnO_nf-L1 upon interaction with metal ions can be attributed to the photoinduced charge transfer (PCT) mechanism.