The Influence of Anions on Electron-Transfer Photochromism of Bipyridinium-Derived Metal–Organic Materials
Jian‐Jun Liu, Jian‐Jun Liu, Shu‐Biao Xia, Yao Liu, Hongbo Suo, Jiaming Liu, Jiaming Liu, Xiang Shen
Abstract
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.