Molecular Design And Application Study Of Visible Light Stimuli-responsive Azobenzene Derivatives

Azobenzene and its derivatives have two different configurations,cis and trans.Under the action of ultraviolet light or heat,cis and trans reversible reactions can occur.It has many advantages.It has important application value as a photomolecular switch and has been widely studied.Two common shortcomings of azobenzene limit their practical application in materials science.One is to induce trans-cis-isomerization by???*excitation under ultraviolet light.Ultraviolet irradiation has high dispersibility and toxicity,which limits the application of azobenzene compounds in the field of biomedicine.The n??*bands of trans and trans isomers overlap largely due to the irradiation in visible light region.In this paper,two new azobenzene compounds have been designed to transform azobenzene compounds driven by ultraviolet light into visible light.The new azobenzene compound is further modified to separate cis and trans isomers in n??*band,and can be converted into two isomers with different colors of visible light,thus broadening its application field.In chapter 1,we briefly introduce three kinds of light-controlled molecular switches with different mechanisms.The mechanism of photoisomerization and the influencing factors of photoisomerization of azobenzene compounds are introduced from the aspects of substituents,intermolecular forces,intramolecular hydrogen bonds and solvents.Based on the photoisomerization properties of azobenzene compounds,the applications of azobenzene compounds in information storage,dye-sensitized batteries and drug release were discussed.Based on the research of azobenzene compounds,it is proposed that azobenzene compounds driven by visible light are more widely used than ultraviolet light.It is introduced from two aspects of research status and application prospect.Finally,according to the current research progress,put forward the research significance and content of the topic of this paper.In chapter 2,density functional theory(DFT)is used to design and systematically study the bridge bonded azobenzene compounds.The two benzene rings of this azobenzene compound are connected by an alkane chain in the adjacent position of the compound,which regulates the wavelength of the photomolecular switch so that it can be driven by visible light.Alkanes of different lengths were selected as bridge bonds to connect azobenzene rings,and the effects of bridge length on geometry,absorption spectra and photoisomerization mechanism were studied.The results show that the alkane chain containing 5 carbon has the least influence on the structure of its azo unit due to the steric hindrance effect of the alkane chain.The alkane chains containing 1 and 2 carbons produce strong absorption peaks in the visible region.Absorption peaks are separated and cis-trans isomerization can be driven by visible light with different colors.In addition,the alkane chain does not change the photoisomerization mechanism of azobenzene,and the dihedral Angle torsion path is still the main one.In chapter 3,density functional theory(DFT)was used to design a novel visible light responsive extended bisazobenzene compound.The effects of ligands,substituents and push-pull electrons on the geometrical structure and optical properties of diazobenzene compounds were analyzed.The results show that when the linkers are linear group 1,3-butadiene and ring group pyrazine,absorption peaks appear in visible region.Under the action of substituent group pushing and pulling electrons,the absorption peak is enhanced and the red shift phenomenon is obvious.Both are the choice of elongated diazobenzene photomolecular switches with superior visible light response.In chapter 4,the reversible cis-trans isomerism of extended diazobenzene molecules on gold surface is simulated by molecular dynamics method.The effects of azobenzene surface covering density,ligands and substituents on cis-trans isomerism of long diazobenzene molecules and the change of surface height when used as molecular motor were studied.Compared with a single azobenzene molecule,the elongated diazobenzene molecule has obvious height variation and orderly Angle distribution due to greater intermolecular force.The intermolecular force can be changed by covering density,ligands and substituents.Chapter 5 is a summary of the whole paper,and prospects the application of elongated azobenzene in biological systems and energy storage materials.In biology,by connecting elongated diazobenzene molecular switches to single helical proteins.When structural transformation is carried out under the irradiation of visible light,the terminal distance changes realize the possibility of light-controlled proteins.In the field of energy storage,elongated bisazobenzene molecules are grafted onto the surface of carbon nanotubes,and the photoinduced trans-cis transformation of azobenzene is utilized to realize the storage of light energy and release heat energy through cis-trans transformation.The whole process is closed cycle,does not produce CO₂and other waste gas,low cost,only need visible light.The obtained enthalpy change(?E_cis-trans)is 2.8494 e V,approximately equal to 274.9252 KJ/mol,which is a kind of energy storage material with excellent performance.