Regulating the Topologies and Photoresponsive Properties of Lanthanum-organic Frameworks.

Metal-organic frameworks (MOFs) show potential application in many domains, in which photochromic MOFs (PMOFs) have received enormous attention. Researchers mainly utilize photoactive ligands to build PMOFs. Recently, the mixed electron donating and accepting ligands strategies have also been used to construct PMOFs driven by the electron transfer between nonphotochromic moieties. However, the potential interligand competition inhibits the formation of PMOFs. Therefore, the exploration of single-ligand-guided assembly is conductive for building PMOFs. Considering the existing electron accepting and donating role of pyridyl and carboxyl, the pyridinecarboxyate derived from the fusion of pyridyl and carboxyl units may serve as single ligand to yield PMOFs. In this work, the coordination assembly of bipyridinedicarboxylate (2,2'-bipyridine-4,4'-dicarboxylic acid, H2bpdc; 1,10-phenanthroline-2,9-dicarboxylic acid, H2pda) and LaCl3 generate two PMOFs, [La(bpdc)(H2O)Cl] (1) and [La(pda)(H2O)2Cl]·2H2O (2). Both complexes feature dinuclear lanthanum as building blocks with differences in the connecting number of likers, in which 1 has (4,8)-connected topology and 2 exhibits sql topology. Their structural differences result in the diversities of photoresponsive functionalities. Compared with reported PMOFs built from photoactive ligands and mixed ligands, this study provides new available categories of single ligand for generating PMOFs and tuning the structure and photoresponsive properties via ligand substitution and external photostimulus.

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

Photochromic metal-organic complexes (PMOCs) have received huge attention of chemists, thanks to their diverse structural characteristic and various available photo-modulate physicochemical functionalities. The organic ligand plays a crucial role in the quest of PMOCs with specific photo-responsive functionalities. The multiple coordination modes of polydentate ligands also provide possibilities for forming isomeric MOCs, which may open a new perspective on the research of PMOCs. The exploration of suitable PMOC systems is significant for the yield of isomeric PMOCs. Taking into account extant PMOCs based on polypyridines and carboxylate as electron acceptors (EAs) and donors (EDs), the covalent fusion of suitable pyridyl and carboxyl species may produce single functionalized ligands bearing ED and EA moieties for the building of novel PMOCs. In this study, the coordination assembly of bipyridinedicarboxylate (2,2'-bipyridine-4,4'-dicarboxylic acid, H2bpdc) and Pb2+ ions generate two isomeric MOCs, [Pb(bpdc)]·H2O (1 and 2), which have the same chemical compositions with main discrepancies in the coordination mode of bpdc2- ligands. As expected, supramolecular isomers 1 and 2 exhibited different photochromic performance, thanks to the distinct microscopic functional structural units. A schematic encryption and anti-counterfeiting device based on complexes 1 and 2 has also been studied. Compared with the extensively studied PMOCs supported by photoactive ligands like pyridinium and naphthalimide-derivatives and PMOCs derived from mixed electron-accepting polydentate N-ligands and electron-donating ligands, our work provides a new idea for building PMOCs based on pyridinecarboxylic acid ligands.

Inserting protonated phenanthroline derivatives into the interchain voids of anionic halometallate units to generate hybrid materials with tunable photochromic performance.

Hybrid photochromic materials (HPMs) have potential applications in numerous fields, such as display, protection, and information storage. The generation of HPMs with tunable photochromic performance is meaningful for the availability of smart photoresponsive materials. As a good platform, crystalline HPMs (CHPMs) provide possibilities to generate desirable products because of their synthetic tunability. To achieve this goal, how to introduce predesigned organic ligands as electron acceptors (EAs) into suitable electron donor (ED) systems is significant for yielding products with hybrid ED-EA structure triggering electron transfer (ET) after photo-stimulus. In this study, inserting protonated 1,10-phenanthroline (phen) (as EAs) and its monosubstituted derivatives 5-Cl-phen and 5-NH2-phen to the interchain voids of anionic halometallate units (as EDs) generated three CHPMs, namely [H-phen][BiCl4] (1), [H-5-Cl-phen][BiCl4]·H2O (2), and [H-5-NH2-phen][BiCl4]·H2O (3). The obtained products featured the same anionic inorganic chains with main differences in the protonated organic guests. As expected, compounds 1-3 displayed apparent photochromism because of the ET from the anionic chains to protonated organic units. Interestingly, the photochromic performance of complexes 1-3 could be tuned by inserting phenanthroline-derivative-guests. This research offers a universal way to engineer the photochromic performance of halometallate-based CHPMs under the guidance of the organic EA design.