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.

Hybrid Photochromic Lanthanide Phosphonate with Multiple Photoresponsive Functionalities.

Hybrid photochromic materials (HPMs) with specific photoresponsive functionality have applications in many fields. The photoinduced electron-transfer (ET) strategy has been proved to be effective in the synthesis of HPMs with diverse photomodulated properties. The exploitation of new electron acceptors (EAs) is meaningful for promoting the development of HPMs. In this work, we introduced a rigid tetraimidazole derivative, 3,3,5,5-tetra(imidazol-1-yl)-1,1-biphenyl (TIBP) as a potential EA, into a metal-diphosphonate (1-hydroxyethylidene-1,1-diphosphonic acid, H4-HEDP) system to explore HPMs and finally obtained a hybrid metal phosphonate (H4-TIBP)0.5·[Dy(H-HEDP) (H2-HEDP)]·H2O (1). 1 features anionic chains composed of diphosphonate and Dy3+ ions. The extra charge is balanced by protonated TIBP cations, which exist in the void of adjacent chains and form H-bonds with Ophosphonate (N-H···O). Upon photostimulation with a Xe lamp (300 W), the crystalline sample 1 exhibited coloration by changing from colorless to pale yellow because of the presence of photoinduced radicals that originated from the ET from Ophosphonate to NTIBP. Along with the coloration, photomodulated fluorescence, magnetism, and proton conductivity were also detected in the photoactivated samples. Different from the reported HPMs based on polypyridine derivatives and photoactive species such as pyridinium and naphthalimide derivatives as EAs, our study provides a new category of EA units to yield HPMs with fascinating photoresponsive functionality via the assembly of polyimidazole derivatives and phosphonate-based supramolecular building blocks.

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.

Modulating the structure and photochromic performance of hybrid metal chlorides with nonphotochromic 1,10-phenanthroline and its derivative.

Hybrid photochromic materias (HPMs), especially crystalline HPMs (CHPMs), have been widely investigated due to their feasibility in maintaining the advantages of each constituent and genearating captivating photomodulated functionality. Metal-organic complexes (MOCs), as promising candidates for fabricating CHPMs, have attracted the interest of researchers. The molecular predesign of ligands plays a crucial role in yielding MOC-based CHPMs with tunable photochromic functionality. Hitherto, a great majority of CHPMs are driven by photosensitive ligands. However, the complicated synthesis and high cost of photosensitive ligands obviously prevent the macro-synthesis and future application of these CHPMs. Thus, it is indispensable to explore novel branches of CHPMs. Herein, we report a series of photochromic solid materials bearing modulated photochromic properties by hybridizing metal chlorides with a nonphotosensitive coplanar dipyridine unit 1,10-phenanthroline (phen) and its derivative 5-chloro-1,10-phenanthroline (5-Cl-phen). The resulting hybrids, [ZnCl2(phen)] (1), [CdCl2(phen)] (2), [PbCl2(phen)] (3), [ZnCl(H2O)(5-Cl-phen)2]Cl·2H2O (4), [Cd2Cl4(5-Cl-phen)2] (5) and [Pb2Cl4(5-Cl-phen)2] (6), exhibit distinct structures from the isolated molecular complexes (1 and 4) to the hybrid chain (2, 3, 5 and 6) because of the distinct coordination mode of central metal ions and chloride ions. After photo-irradiation with a Xe-lamp, all complexes, as expected, exhibited apparent color change because of the photoinduced electron transfer (ET) between coordinated chloride ions (Cl-) as electron donors (EDs) and the coordinated coplanar phen and 5-Cl-phen species as electron acceptors (EAs). More importantly, the photochromic performance of the title complexes could be modulated by phen and 5-Cl-phen. This study provides a general and facile way for modulating the structure and photochromic performance of hybrid metal chlorides with phen or phen-based derivatives under the synergy of crystalline engineering strategy and ET mechanism.