Series of viologen-based metal-oxalate frameworks showing ultrafast-response photo/electrochromic and UV detection behavior

The construction of molecular crystalline materials with well-defined crystal structures and ultrafast multi-stimuli responsive behaviours is of extraordinary significance for practical applications and scientific implications. In this context, three multi-stimuli-responsive functional metal-oxalate frameworks, {[Cd2(m-Hbcbp)(C2O4)2.5]·CH3CN}n (1), {(m-H2bcbp)·[Zn2(C2O4)3]·2.8H2O}n (2), and {(bpync)[Zn2(C2O4)3]}n (3; m-H2bcbp = 1,1′-bis(3-carboxyphenyl)-4,4′-bipyridinium; bpync = 1,1′-bis(3,5-dimethyl-1H-pyrazole-4-yl)-4,4′-bipyridinium) were successfully prepared and comprehensively characterized. All of the compounds exhibit ultrafast and reversible photochromic and electrochromic dual-responsive behaviors. Furthermore, based on the well-defined crystal structure before and after irradiation and different responsive behaviors, the photoinduced electron transfer (PIET) process and structure-activity relationship were further explored. In addition, considering the excellent photochromic performance, the function filter paper and smart organic glass were successfully prepared and used for ink-free printing and UV light detection.