Electrofluorochromic Detection of Cyanide Anions Using a Nanoporous Polymer Electrode and the Detection Mechanism

An electrofluorochromic (EFC) conjugated copolymer ( P EFC ) containing carbazole and benzothiadiazole (BTD) moieties is synthesized through Suzuki coupling followed by electrochemical polymerization, resulting in a nanoporous EFC polymer electrode. The electrode exhibits high sensitivity and selectivity in the EFC detection of cyanide anions (CN − ) in largely aqueous electrolyte (67 vol % water) because electrochemical oxidation of P EFC leads to significant fluorescence quenching, and the presence of different concentrations (1 to 100 μ M ) of CN − in the electrolyte can weaken the oxidative quenching to substantially different extents. Although P EFC is hydrophobic in the neutral state, it is converted to radical cation/dication states upon oxidation, rendering the P EFC some hydrophilicity. Moreover, its nanoporous morphology provides a large surface area and short diffusion distance, facilitating the movement of CN − in the electrolyte into the P EFC film to interact with receptors. Density functional theory calculations show that the noncovalent interaction between electron‐deficient BTD and nucleophilic CN − is energy favorable in the oxidized states in both aqueous and organic media, suggesting that the specific π − –π + interaction plays the main role in the CN − detection.