Ligand Tailoring and Functional Group Fusion Strategy for Developing Photochromic Compounds: A Case Study for Pyridinedicarboxylic Acid

Hybrid photochromic materials (HPMs) can produce novel photoresponsive properties, thanks to the synergistic effect of each component. One of the widely explored ways toward a novel HPM system is the utilization of the phototriggered electron transfer (ET) mechanism. In this work, the photochromic functionality of pyridinedicarboxylic acid with the chemical formula of H2-L1 center dot H2O (1, H2-L1 = 2,6-pyridinedicarboxylic acid) and related metal-organic complexes (MOCs), [Zn(HL1)2]center dot 2.5H2O (2), [Pb(L2)] (3, H2-L2 = 2,4-pyridinedicarboxylic acid), [In(L2)(HL2)]center dot 2H2O (4), and [Eu3(L2)4(OH)(H2O)2]center dot 11H2O (5), has been first proved via the ligand tailoring and functional group fusion strategy. The photogenerated radicals derived from ET were experimentally characterized. Different from the previously investigated HPMs based on electron-deficient pyridiniums and rigid polydentate N-ligands as electron acceptors (EAs), this work exploits a new category of ligands for developing HPMs and investigating the underlying photoresponsive functionalities. Considering the large varieties of carboxylate and pyridine moieties, this study offers a general strategy for developing new HPMs and exploring the potential photoresponsive functionality via integrating the carboxylic groups as electron donors (EDs) and pyridyl groups as EAs in the single ligand.