A Multifunctional Coordination Polymer Constructed by Viologen Derivatives: Photochromism, Chemochromism, and MnO4-Sensing

A multifunctional Cd-based coordination polymer based on a viologen derivative and a secondary carboxylic ligand, phthalic acid), has been solvothermally synthesized and structurally characterized. Compound 1 is a 3D framework built on {Cd2(pta)2 (H2O)}n net with square channels which intalls bcbp ligands at the diagonal position of the two adjacent square channels. Notably, compound 1 exhibits a reversible photochromic transformation between yellowish gray and dark green under xenon light irradiation, which should be attributed to the formation of free viologen radicals. Furthermore, compound 1 also displays a chemochromic phenomenon from yellowish gray to dark green after exposure to ammonia and hydrazine, which could be ascribed to the generation of viologen radicals and charge-transfer complexes triggered by nucleophilic attack of electron-rich ammonia and hydrazine molecules to the electron-deficient viologen moiety in the bcbp ligand. Moreover, compound 1 is capable of quickly and selectively detecting MnO4- with a high quenching coefficient and a low limit of detection via a luminescent quenching process caused by the competitive absorption of excitation energy.