Synthesis And Properties Of Lead-Halide-Based Organic-Inorganic Hybrid Chromic Materials

Organic-inorganic photochromic hybrid materials based on electron donor-acceptor units have potential or practical applications in protection,data storage,switches,sensors,displays,photoelectric equipments and other fields due to their excellent response to external stimuli and tunable compositions,structures and properties.Enrichment of donor/acceptor in composition,structure,and electron donating/accepting ability through reasonably selecting electron donors/acceptors is the key to modulate the internal electronic behaviors and chromic properties of hybrid materials.Semiconductive hybrid lead halides,especially hybrid lead iodide,have been widely used in photoluminescence,solar cells and photocatalysis because their flexible and diverse structures,adjustable band structures,lower optical band gaps,large absorption coefficient and ease of fabrication.Although they also exhibit good photo-/thermo-/mechanochromic properties,study on this kind of chromic material is still rare.The combination of suitable organic acceptors with lead halides to systematically modulate the interfacial relationship of donor-acceptor and chromic performance is of great significance for further understanding the relationship of composition-structure-property and developing new multifunctional chromic materials,Herein,six iodoplumbate hybrids[MBI][PbI₃]（1）、[EBI][PbI₃]（2）,[BzBI][PbI₃]-A（3）,[BzBI][PbI₃]-B（4）,[MBTz][PbI₃]（5）,[BzBTz][PbI₃]（6）have been synthesized by using alkylated/benzylation benzimidazole/benzotriazole（BI/BTz）cations as structure-directing agents and electron acceptors.On the other hand,three coordination polymers containing lead halides[Pb（4-CAPO）Cl]（7）,[Pb（4-CAPO）Br]（8）,[Pb（4-CAPO）I]（9）have been synthesized by selecting 4-carboxypyridine oxynitride（4-CAPO）as organic ligand and electron acceptor.The structures and chromic properties of these hybrids have been well characterized,and the intrinsic relationship of composition-structure-function has been investigated.The main conclusions are as follows:1、Compounds 1-6 contain similar[PbI₃]_n^n?anion chains,revealing the similar structure-directing effect of the alkyl/benzylated BI and BTz cations and the unique crystallization habit of the iodoplumbate frameworks.2、Compounds 1,2 and 5 are photochromic-silent,while 3,4 and 6 show different photoinduced intermolecular electron transfer and photochromic behaviors,revealing the modulating effect of different cations on interfacial relationship of electron donor-acceptor and intermolecular electron transfer channels.3、Compounds 1、3、4、5 exhibit reversible tribochromism generated from the interconversion between crystalline and amorphous states.Deformation of the[PbI₃]_n^n?chains upon grinding leads to changes in internal electronic structures and thus changes in absorption spectra of hybrids.Generally,the smaller the crystal density and the greater the chain distortion,the more obvious the color change.The benzylated BI iodoplumbate hybrids 3 and4 possess the rare difunctional properties of both photochromism and tribochromism.4、The assembly of 4-CAPO electron acceptor and lead halide electron donors construct three isostructural 3D coordination polymers 7-9.Although 7-9 possess similar packing patterns,they show different light-induced intermolecular electron transfer and photoresponsive behaviors,in which only complex 9 containing lead iodide exhibits obvious electron transfer photochromism.The types of halogens（Cl,Br and I）significantly modulate the electron-donating ability of donors and the photochromic properties of complexes.9exhibits same photoresponsive rate and coloration contrast when irradiated by ultraviolet light and visible light,respectively,indicating that photochromism should attributed to excitation of lead iodide electron donor,occurrence of electron transfer and generation of organic radicals.