Polychromatic fluorescent sensor for hydrogen sulfate anion recognition based on molecular conformation transformation

Detection of hydrogen sulfate anion (HSO₄^-) is becoming crucial in biology, environmental sciences, and catalysis scientific fields. Herein, we demonstrate a strategy for precisely and visually detecting hydrogen sulfate anion (HSO₄^-) by polychromic fluorescence variations based on molecular conformation transformation in the mixed solvent of acetonitrile and water (v/v = 4:1) with the detection limit of 5.08 μM. With the combination of a flexible skeleton of N,N’-diphenyl-dihydrodibenzo[a,c]-phenazine (DPAC) and two recognition ‘claws’ of triazole units, the fluorescent sensor DPAC-Tz was designed and synthesized. Depending on the non-covalent binding affinity of triazole units with hydrogen sulfate anions, the bend-to-twisted conformation evolution of DPAC moiety in the excited state was restricted, resulting in the significant fluorescent color conversion from orange to blue. The non-covalent interaction mode was investigated by ¹H NMR spectroscopic analysis and density functional theory (DFT) calculations as well as IGMH analysis, and the application of DPAC-Tz on hydrogen sulfate anions was demonstrated in the living cells imaging. This study explicitly reveals the application prospect of combining flexible scaffolds with dynamic structural evolution and non-covalent intermolecular interactions for analyte sensing, thereby inspiring the exploitation of polychromatic fluorescent sensors with high selectivity and visibility in various chemical detections.