Photo-/Thermochromic Bipyridyltriazolium Chlorometallates

The intermolecular electron transfer and intermolecular charge transfer materials have aroused more and more attention in the recent years due to the different responses to the diverse external stimulus such as light,heat and electricity and the potential applications in the fields of photochemistry,thermochemistry,molecular electronic,photosynthesis and solar energy transfer,especially,the photo-/thermochromic materials are great interest because of their assessment of electronic behavior,and potential values in optical switches,thermoswitches.Although different electron accepter based photochromic materials have been reported and matching rules and electron behaviors between acceptors and various donors have been theoretically and experimentally investigated deeply by scientists in solution,the dual photo-/thermochromism are rare because of the thermo-induced charge recombination and the oxidation of the color organic radical by O2 in air,which mainly include some viologen based coordination complexes and molecular sieves.Therefore,reasonable introduction of new strong acceptors is a practical route for understanding deeply and modulating effectively the successive photo-/thermo-responsive behaviors and the matching behavior in the electron donor-acceptor system.Because of the effective modulating on pyridine N and the internal electron in a wide range with respect to the widely used viologen,diprotonated bpt could be used as ideal electron acceptor for studying the photo-/thermol-response behaviors in the electron donor-acceptor system.In this paper,using diprotonated 3,5-bis(pyridine-X-yl)-1,2,4-triazole(bpt,X=2,4,)as electron acceptor,we synthesized six chlorobismuthates and chloro-antimonates photo-/thermochromic hybrids:(2-bpt)2[Bi2Cl10(H2O)]·5H2O(1),(2-bpt)4[Bi Cl6(Cl)]2·6H2O(2),(2-bpt)[Sb Cl5]·2Cl(3),(4-bpt)2[Bi Cl5]·2Cl(4),(4-bpt)3[Bi Cl6]2(5),(4-bpt)[Sb Cl5][Sb Cl4]·H3O(6).Measuring the structures by Single-crystal X-ray diffractometer and combining UV-vis diffuse reflectance,Electron paramagnetic resonance indicate that:(1)the effect of anion size of the chlorobismuthate: the chlorobismuthates with the same electron acceptor display functional properties from no possessing photo-/thermochromic behavior to possessing photo-/thermochromic behavior as the increase of the anion size,indicating that the larger anion size is,the stronger the giving electron capacity of the donor.(2)the effect of the bpt with the different pyridine N: under the chlorobismuthates with the same electron donor,2 possesses photochromism,but 5 do not,indicating that the place of the pyridine N in the bpt play a key role in modulating on the electron accepting capacity of the acceptor: 4-bpt > 2-bpt.(3)the effect of the metal center of the chlorometallates donor: 1 possesses dual photo-/thermochromism but 3 only possesses photochromism,indicating that the metal center of the electron donor is a necessary factor for modulating electron giving capacity.