Construction of enhanced fluorescence sensors in aqueous media by cation regulation and hybridization

Abstract

For sensing application, a salicylacylhydrazone (H2L) with multiple binding sites which was condensed by salicylhydrazide and 4-acylpyrazolone, H2L = 4-Benzoyl-3-methyl-l-phenyl-5-pyrazolone-benzoic acid hydrazide was prepared. Fluorescence studies indicate that H2L could be used as turn-on sensors to distinguish between Cd2+ and Zn2+ in Hepes buffer solution (pH = 6.8) and the origin of the specificity of the fluorescence recognition was disclosed through 1H NMR spectra, UV–Vis spectra, ESI mass spectra, X-ray single crystal diffraction and DFT calculations. H2L test silica sheets were further prepared to offer easy and real-time detection of Cd2+ and Zn2+ ions. Furthermore, the in situ system generated from the sensing of Zn2+ and Cd2+ (ZnHL and CdHL) showed good relay recognition ability for picric acid (PA) via fluorescence quenching. The recognition mechanism of PA could be attributed to the multi-quenching mechanism dominated by the competitive absorption with PET effect and hydrogen bond being assistance when density functional theory calculations and multiple experimental evidences, including ESI mass spectrum, 1H NMR spectra as well as UV–Vis absorption are combined. To enhance their sensing ability together with the convenience of detection, the hybrid films of ZnHL@PMMA and CdHL@PMMA are prepared by doping them to polymethyl methacrylate (PMMA) matrix to improve their fluorescence performance, chemical stability, sensitivity, cheapness and quickness.