Photochromic Supramolecular Isomers Derived from Pb(II)-Bipyridinedicarboxylate Complexes

Photochromic metal-organic complexes (PMOCs) havereceivedhuge attention of chemists, thanks to their diverse structural characteristicand various available photo-modulate physicochemical functionalities.The organic ligand plays a crucial role in the quest of PMOCs withspecific photo-responsive functionalities. The multiple coordinationmodes of polydentate ligands also provide possibilities for formingisomeric MOCs, which may open a new perspective on the research ofPMOCs. The exploration of suitable PMOC systems is significant forthe yield of isomeric PMOCs. Taking into account extant PMOCs basedon polypyridines and carboxylate as electron acceptors (EAs) and donors(EDs), the covalent fusion of suitable pyridyl and carboxyl speciesmay produce single functionalized ligands bearing ED and EA moietiesfor the building of novel PMOCs. In this study, the coordination assemblyof bipyridinedicarboxylate (2,2 '-bipyridine-4,4 '-dicarboxylicacid, H(2)bpdc) and Pb2+ ions generate two isomericMOCs, [Pb-(bpdc)]center dot H2O (1 and 2), which have the same chemical compositions with main discrepanciesin the coordination mode of bpdc(2-) ligands. As expected,supramolecular isomers 1 and 2 exhibiteddifferent photochromic performance, thanks to the distinct microscopicfunctional structural units. A schematic encryption and anti-counterfeitingdevice based on complexes 1 and 2 has alsobeen studied. Compared with the extensively studied PMOCs supportedby photoactive ligands like pyridinium and naphthalimide-derivativesand PMOCs derived from mixed electron-accepting polydentate N-ligandsand electron-donating ligands, our work provides a new idea for buildingPMOCs based on pyridinecarboxylic acid ligands. Two isomeric photochromic metal-organiccomplexes(PMOCs) based on pyridinecarboxylate were obtained. Compared withthe broadly investigated PMOCs supported by photoactive ligands andPMOCs derived from mixed nonphotoactive ligands, this work providesa new idea for developing PMOCs based on single ligands.