Two photochromic two-dimensional Zn(II)-MOFs based on a carboxybenzyl viologen ligand

Two new Zn(II) metal-organic frameworks (MOFs) {[Zn(Bpybc)0.5 (m-BDC)(H2O)]·2H2O}n (1) and {[Zn(H2Bpybc)(BTEC)(H2O)2]·H2O}n (2) have been successfully synthesized, where 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium dichloride (H2BpybcCl2) is used to react as the predesigned ligand with two kinds of aromatic carboxylic acids (1,3-benzenedicarboxylic acid = m-H2BDC, 1,2,4,5-benzenetetracarboxylic acid = H4BTEC) as the secondary building linkers. Both two compounds own two-dimensional (2D) layered structures. In addition, compounds 1 and 2 display reversible photochromism, which is associated with the generation of free radicals via photoinduced electron transfer. Simultaneously, the photomodulated fluorescent properties and their potential applications in ink-less and erasable printing were also studied.