Stimuli‐Responsive Cd(II) Coordination Polymer Based on Viologen Exhibiting Photochromism, Photocontrolled Fluorescence, Ammonia Vapor Sensing, and Anti‐Counterfeiting

Abstract Photochromic materials containing viologen have shown broad practical applications, but synthesizing multifunctional photochromic materials remains a significant challenge. In this work, a novel Cd(II) coordination polymer, {[Cd 4 (BCMBPY) 2 (BTEC) 2 ]·4H 2 O} n ( 1 ), has been successfully synthesized under solvothermal conditions based on viologen ligand 1,1′‐bis [(2‐carboxybipheny‐4‐yl)methyl]‐4,4′‐bipyridinium dichloride (H 2 BCMBPY·2Cl), 1,2,4,5‐benzenetetracarboxylic acid (H 4 BTEC), and Cd(NO 3 ) 2 ·4H 2 O. Single crystal X‐ray diffraction analysis reveals that Cd(II) ions connect BCMBPY and BTEC 4‐ anions to form two‐dimensional (2D) layered structure in 1 . Upon exposure to a 300 W Xe lamp, 1 transitions from beige to light green rapidly within 15 s and exhibits photocontrolled fluorescence with the increasing irradiation time. The discoloration mechanism of coordination polymer 1 was investigated via time‐dependent density functional theory (TDDFT). Additionally, 1 can detect ammonia vapor, changing from beige to dark green upon exposure. Furthermore, 1 has potential application ability in anti‐counterfeiting.