Carboxyphenyl-terpyridine-based series of gels for procedural visual recognition of multi-anions

Abstract

4-[2,2′:6′,2′′-Terpyridine]-4′-ylbenzoic acid (Hcptpy), with multiple coordination sites and large π–π stacking backbone, proved an excellent ligand for gels formation. Interestingly, the Hcptpy alone successfully formed white and yellow gels via introducing H₂PO₄⁻ and Cr₂O₇²⁻ respectively. Except for constructing metal organic gels (MOGs) with Zn²⁺, Tb³⁺ and Al³⁺, Hcptpy could also form MOGs with 9 other kinds of metal ions. Based on color with the MOGs formation under daylight or 365 nm UV lamp, 6 kinds of metal ions were specifically recognized. Besides, the prepared MOGs also possess stimuli response property to anions. In view of the characteristic of Hcptpy and synthetic MOGs, the step-by-step recognition anion progress was established including Hcptpy, Zn-MOG, Tb-MOG, Eu-MOG and Cd-MOG, successfully realized the selective and visual identification 12 kinds of anions, which may open up routes to rational design and preparation novel stimuli-responsive MOG materials for sensing application.