As a new class of multifunctional materials, photochromic materials have received much attention due to their potential applications in many fields. In order to investigate the effect of anions on the electron-transfer properties of photochromic coordination polymers, five bipyridinium-based complexes with different anions, namely [Zn­(bcbpy)­(H2O)­(Cl)]·Cl·2H2O (1), [Zn­(bcbpy)­(H2O)­(Br)]·Br·2H2O (2), [Zn­(bcbpy)2]·2I·6H2O (3), [Zn­(bcbpy)2]·2ClO4·6.4H2O (4), and [Zn­(bcbpy)­(N3)2]·3H2O (5) (H2bcbpy·2Cl = 1,1′-bis­(3-carboxylatobenzyl)-4,4′-bipyridinium dichloride), were synthesized via self-assembly and were characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. Due to different charge transfer interactions between the anions and the electron-deficient bipyridinium moiety, these complexes exhibit different electron-transfer photochromic behaviors. Specifically, complexes 1, 2, 4, and 5 were photochromic but 3 was not. This difference could be attributed to a stronger charge transfer interaction in complex 3 in comparison to complexes 1, 2, 4, and 5, as well as the heavy-atom effect of iodine. It is expected that this study will provide a new perspective for the rational design and synthesis of novel photochromic materials.

The insertion of electron-rich iodoplumbate nanowires and nanolayers into layered electron-deficient metal-viologen frameworks leads to two donor-acceptor hybrid structures, respectively, which exhibit interesting semiconductor behaviors. Due to the bicontinuous donor and acceptor components, both of them exhibit highly efficient photocatalytic degradation activities over organic dyes under visible light irradiation compared to those of other iodoplumbate hybrid materials.

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