Syntheses And Characterization Of Photochromic Halometallate Hybrids Directed By Nicotinohydrazide Derivatives

Compared to the pure inorganic and organic photochromic materials,photochromic organic-inorganic hybrids based on the donor-acceptor units are particularly preferred due to their compositional and structural flexibility as well as potential synergistic effect.Generally,these hybrid materials preferentially employ polycyclic aromatic compounds such as viologens and 1,4,5,8-naphthalenediimides(NDIs)as strong electron acceptors,which restricts the matching electron donors to some strong Lewis bases,such as chlorometallates,metallophosphates,and organic groups/molecules containing O as donor atom.Therefore,variation of electron donors and acceptors provides an effective route,and research on the matching rules between electron acceptors and donors is very significant for the design and development of new photochromic materials.Herein,employing protonated/methylated nicotinohydrazide and isoniazid as moderate electron acceptors,nine halometallate hybrids have been synthesized.Their structures and photochromic properties have been characterized by single-crystal/power X-ray diffraction,IR,EPR,XPS and UV-vis spectra,and so on.The influence of composition,structure,electron accepting/donating capability,as well as donor-acceptor matching rule on the photochromic behavior is analyzed.The main conclusions are listed as follow:(1)The photochromism of these hybrids can be attributed to the photoinduced electron transfer(PET)from electron donors to acceptors and consequent generation of colored organic radicals.(2)It is the iodozincate hybrid 1 rather than bromozincate 2 and chlorozincate 3undergoes impressive PET and photochromism,implying the unique donor-acceptor matching rule for moderate electron acceptor HNH2+(HNH2+ =protonated nicotinohydrazide)different from that for strong acceptor viologens.(3)For hybrids 4-7 containing the same electron donor CdI42-,the intermolecular charge transfer(CT)increases while the PET and photochromic behavior decrease with the increase of electron accepting ability of acceptors.(4)The formation of mixed valence copper in hybrids 8-9 has a promoting effect on PET process and photochromism.The size of the inorganic donors can significantly influence the electron donating ability of donors,the higher the degree of anion aggregation,the faster the photoresponsive rate of iodocuprate hybrids.