Design and synthesis of two functional coordination polymers based on the 1,1′-bis(3-carboxybenzyl)-4,4′-bipyridinium ligand†

Based on the viologen ligand 1,1′-bis(3-carboxylatobenzyl)-4,4′-bipyridinium dichloride (H₂BcbpyCl₂) as the functional subject and two aromatic carboxylic acids (m-H₂BDC = 1,3-benzenedicarboxylic acid and H₄BTEC = 1,2,4,5-benzenetetracarboxylic acid) as auxiliary ligands, two Zn(II)-based coordination polymers, formulated as [Zn(Bcbpy)_0.5(m-BDC)]_n (1) and [Zn(Bcbpy)_0.5(BTEC)_0.5(H₂O)]_n (2), have been successfully prepared by solvothermal strategies. Compounds 1 and 2 both have a three-dimensional framework. The two compounds demonstrate reversible photochromic properties owing to the formation of viologen radicals via photoinduced electron transfer. In addition, the photomodulated fluorescence and ink-free erasable printing properties were also studied, which enriched the study of the photophysical properties of the crystals.