Tetra-cyanostilbene macrocycle: An effective “turn-on” fluorescence sensor for oxalic acid in aqueous media

Abstract

• A novel tetra-cyanostilbene macrocycle was synthesized. • It exhibited “turn-on” fluorescence on sensing oxalic acid in aqueous media. • The detection limits was 3.82 × 10 −6 M for oxalic acid. • The sensing mechanism was clarified as oxalic acid in the cavity of the macrocycle. • It was applied on the detection of oxalic acid in test paper, taros and rust treatment. Although some detection methods for oxalic acid have been reported, the rapid, simple and on-site detection on oxalic acid was rarely presented. In this work, a “turn-on” fluorescence sensor for oxalic acid was realized by the simple and on-site procedure in aqueous media. A tetra-cyanostilbene macrocycle was synthesized by simple “2 + 2” condensation in 72 % yield. It displayed the strong “turn-on” blue fluorescence on selectively detecting oxalic acid among various ions and biomolecules. It possessed the high sensing sensitiveness with the detection limit of 3.82 × 10 −6 M. The sensing mechanism was clarified by pH influence on complexation, fluorescence Jobs’ plot, MS spectra, and 1 H NMR spectra, confirming that non-dissociated oxalic acid was bound in the cavity of the macrocycle based on hydrogen bonds. This sensing ability for oxalic acid was successfully applied in test paper, on-site detection for real samples of taros and rust treatment, suggesting the good application prospect in the rapid, simple and on-site detection for oxalic acid in daily life and industry.