Two cases of bipyridinium-based metal-organic frameworks: Syntheses, structures, photochromic behaviors.

Abstract Two novel bipyridinium-based metal–organic frameworks Zn[(pbpy) 0.5 (m-BDC)Cl]·1.5H 2 O(1) and Cd[(pbpy) 0.5 (m-BDC)Cl]·H 2 O(2).(pbpycl 2 = 1,1′-[1,4-phenylenebis-(methylene)]bis(4,4′-bipyridinium)–dichloride) have been synthesized and structurally characterized by single crystal X-ray crystallography. Both of them show 2D layered window structures. When they are irradiated by 300 W Xenon lamp, both of them exhibit photochromic behaviors which are attributed to the process of intermolecular electron transfer to generate pbpycl 2 free radicals. These processes have been demonstrated by UV–Vis absorption characterization analysis, electron spin resonance (ESR). The photoproduct of compound 1 is more stable than compound 2 in air. Photochromic mechanisms and the relationships between structures and properties have been discussed adequately. Graphical abstract Two cases of metal-controlled photosensitive bipyridinium-based metal-organic frameworks, these compounds exhibit reversible photochromic behaviors. Unlabelled Image Highlights • Two cases of novel MOFs have been synthesized. • These compounds exhibit photochromic properties. • They have different color fading time. [ABSTRACT FROM AUTHOR]