Synthesis and properties of a novel photochromic metal organic framework for rapid amine selective sensing and Cr2O72− detection

A new photochromic metal organic frameworks (MOFs) have been synthesized by using a viologen ligand, named 1,1′-bis(3,5-carboxylatobenzyl)-(4,4′-bipyridinium) dichloride (H4bdcbpy•2Cl) and Cd(NO3)2·4H2O. This MOF (Cd-bdcbpy) features a three-dimensional (3D) framework structure, exhibiting photochromic properties under the irradiation of white light, blue light, UV light and heat with obvious color change from light yellow to dark green. Meanwhile, Cd-bdcbpy displays a visible color change to the naked eye when exposed to different organic amine molecules (ammonia, aniline, o-methylaniline and diphenylamine). Moreover, the detection of ammonia has been confirmed by the visual color changing phenomenon and luminescence quenching experiment and it can detect ammonia in very low concentrations (10-6 ​M). Attractively, through luminescence quenching, Cd-bdcbpy can be used as a multi response sensor for Cr2O72− anion in aqueous solution.