Synthesis And Properties Of Hybrid Compounds Based On Viologen Derivative Ligands

Viologen hybrid materials have attracted great attention due to their attractive topological structure and potential applications such as smart response materials,optical switching,sensing,electrochemical devices,non-linear optics and so on.The introduction of the viologen derivative ligands as active group into the organic-inorganic hybrid framework structure will result excellent discoloring properties.As a class of excellent electron acceptors,they interact with donors under external stimuli,and have reversible redox reactions with the color changes.In this paper,Ten inorganic-organic hybrid compounds were synthesized by self-assembly with metal and viologen derivatives,and their stimuli responsive properties and principles were studied respectively.It is divided into the following five parts:1.This paper briefly introduces the research background,application and classification of viologen-based color-changing materials,and systematically introduces the development of such materials respond to mono-stimulus and multi-stimuli.At the same time,the theoretical knowledge for the design and self-assembly of viologen derivatives was introduced in detail,and the chromic principle of such compounds was further elaborated.2.Two novel structures with symmetric viologen carboxylic acid ligand H₂bpybcCl₂:[Zn₇（Bpybc）₃（o-BDC）₆]·2NO₃·6H₂O（1）and[MnCl₂（bpybc）]·4H₂O（2）have been synthesized.1 is a rare seven-fold interspersed three-dimensional metal framework with Anderson-like clusters.Surprisingly,1 can respond visually various external stimuli,such as ultraviolet light,soft X-ray,temperature and electric field,and can selectively sense a variety of small organic amines.This excellent chromic property is mainly due to that the abundant O atoms in the Anderson-like clusters are favorable for forming much more electron transfer pathways and further improving the possibility for the effective electron transfer to happen under the external stimuli.While complex 2 has a one-dimensional chain-like framework structure,which exhibits rapid coloring behavior only under an inert atmosphere and 365 nm ultraviolet light irradiation.And the colored compound 2’can rapidly discolor when exposed to oxygen,indicating that 2 has potential applications in O₂ detector,molecular switch and so on.3.Six compounds[Hipbp·H₂O]（3）,[Hipbp·2H₂O]（4）,[（Hipbp）·（o-H₂BDC）·H₂O)]（5）,[Mg₂（ipbp）₂（BDC）（H₂O）₉]（6）,[La（NO₃）₂（ipbp）（H₂O）]（7）and[Eu（NO₃）₂（ipbp）₂（m-BDC）（H₂O）₂]·H₂O（8）have been synthesized by using asymmetric carboxylic acid carboxylic acid ligand H₂ipbpCl as the photosensitive group.Among them,3,5 and 6 exhibite rapidly response to ultraviolet light,while 4,7 and 8 can not change color under different external stimuli.Both 3 and 4 only contain ipbp electron-deficient ligand and free water molecules.Generally speaking,the electron donating groups are carboxyl oxygen atoms,halogen atoms or pseudohalogen atoms.In 3 and 4,the distance between carboxyl oxygen atoms and N in viologen ligands is too large to complete photoinduced electron transfer.However,compound 3 still exhibits a high sensitive response to ultraviolet light.After an in-depth analysis of the structure,the distance between the lattice water molecule O and the viologen ligand N is appropriate in 3 and the distance of 4 is too large,which should be the reason why only compound 3 has fast photochromic behavior.All these facts have strongly proved that lattice water molecules can be used as electron donors.Interestingly,3also exhibits excellent second-order nonlinear optical（NLO）switching properties.The NLO intensity ratio is as high as 6.42 times before and after coloration,which indicates that 3 has potential applications in various fields such as molecular luminescence,data storage and glare protection.4.Two novel coordination polymers were synthesized by self-assembly of viologen carboxylic acid ligand[m-H₂bpybc]Cl₂ and transition metal:[Cd（m-bpybc）（BDC）（H₂O）]（9）and Mn₂Cl₄（m-bpybc）（H₂O）₄（10）.Compound 9 has reversible photochromic behavior and is highly sensitive to UV and natural light.Surprisingly,it can also respond quickly to soft and hard X-rays.the colored 9 can recover when placed in dark for a long time or heated at 120°C in air atmosphere.Therefore,compound 9 is an excellent light-responsive smart material（especially for soft and hard X-ray）.Compound 10 can change its color only under ultraviolet light,and the colored process is rather slow.5.Summarize my work and look forward to the research prospects of this topic.