Photochromism of four 1D coordination polymers based on 1-(2-carboxyethyl)-4,4′-bipyridinium ligand

Photoresponsive viologen units have been widely used to impart metal-organic materials with photochromic properties. Herein, four novel one-dimensional (1D) double chain-like coordination polymers (CPs) {[Ni0.5(CBbpy) (H2O)]Br·H2O}n (1), {[Co0.5(CBbpy) (H2O)]Br·H2O}n (2), {[Cu(CBbpy)2(H2O)]Br2·H2O}n (3), {[Cu(CBbpy)2(H2O)]Cl·Br·2H2O}n (4) based on 1-(2-carboxyethyl)-4,4′-bipyridinium bromide (HCBbpyBr) with different metal ions (Ni2+, Co2+, Cu2+, Cu+) have been prepared where the CBbpy molecules act as bidentate N- and O-donor ligands in the four polymers. The crystal structures and photochromic properties of compounds 1–4 are studied. Compounds 1 and 2 have no photochromism observed, while compound 3 exhibits reversible electron-transfer (ET) photochromism and compound 4 exhibits a near irreversible ET color change. Four compounds have similar structure but different photochromic properties, the effects of metal ions and counter anions on the photochromic behaviors of four compounds have been explored. [Display omitted] •Four novel similar 1D coordination polymers based on the CBbpy ligand have been prepared.•The crystal structures and photochromic properties are studied.•The effects of metal ions and counter anions on the photochromic behavior have been explored.