Synthesis, crystal structures, photochromism and selective luminescence sensing property of Zn/Cd-viologen coordination polymers

Three Zn/Cd-viologen coordination polymers (CPs), namely, {Zn[(bcbpy)0.5(ipa)(H2O)]·H2O}n (1), {Zn[(bcbpy)0.5(ipa)(H2O)0.5]·H2O}n (2), and {Cd[(bcbpy)(SO4)]·2H2O}n (3), have been constructed using aromatic carboxylic acid and viologen-derived ligands, where H2bcbpy·2Cl represents 1,1′-bis((4-carboxyphenyl)-4,4′-bipyridine) dichloride and H2ipa stands for isophthalic acid. All three CPs display photochromic properties, transforming from yellow to dark blue upon irradiation with a xenon lamp. Notably, the photoresponse rates vary among these CPs, with compound 1 showing the fastest photoresponse, followed closely by compounds 2 and 3. Furthermore, CPs 1, 2, and 3 display a unique sensitivity to different concentrations of Cr2O72- anion solutions. When immersed in these solutions, the compounds exhibit varying degrees of fluorescence quenching effects, allowing for the monitoring of even the lowest ion concentrations. Additionally, upon exposure to ammonia vapor, the three compounds undergo a color change from yellow to dark brown, indicating their sensitivity to ammonia vapor.