β-cyclodextrin and calix[4]arene-functionalized thieno[3,2-b]thiophene based polymers as fluorescent ion sensors

Design, synthesis, and applications of four novel thienothiophene-based polymers as sensing probes (G1-CD, G2-CD, G1-Cal, and G2-Cal), incorporating π-bridges of thiophene (T) and biphenyl (BP) benefiting from the unique cone-shaped structure and intramolecular interactions of β-cyclodextrin and calix[4]arene, are reported. They exhibited remarkable fluorescent alterations in response to Hg²⁺, Fe³⁺, Ni²⁺, and Cu²⁺. Their syntheses involved Suzuki coupling, and a comprehensive analysis of the optical and electronic properties of the resulting polymers was conducted using UV–Vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Photophysical characterizations of these novel polymers showed a remarkable mega Stokes shift, reaching up to 162 nm and optic/electronic band gaps between 1.95 and 2.92 eV. Notably, G2-CD, functionalized with β-cyclodextrin, stands out as the most promising sensor, demonstrating superior sensitivity and selectivity in detecting Hg²⁺ ions with a remarkable turn-off fluorescence response down to concentrations as low as 1 ppm. This research contributes to advancing the development of electronically and optically responsive materials, with potential applications in the sensitive detection of biologically and toxicologically significant ions.