Preparation And Properties Of Azophenyl Photo-induced Phase Change Solar Thermal Fuels

Azobenzene and its derivatives（AZs）are considered to be promising candidates for the preparation of solar thermal fuel（STF）due to their unique photoisomerization process,which enables controllable conversion between the cis conformation with higher energy state and the trans conformation with lower energy state.However,due to its low energy storage density and short half-life,the application in STF of AZs is greatly limited.Therefore,the design and preparation of azobenzene derivatives with high energy storage density has attracted extensive attention.In this paper,a series of azobenzene derivatives with different alkyl chain structures are designed and synthesized,and the melting points of their cis and trans conformations are lowered,so that the melting point of the trans conformation is higher than room temperature,and the melting point of the cis conformation is lower than room temperature.Achieving controllable photoconversion between solid/liquid two-phase states of azobenzene derivatives at room temperature.Further,combined with the latent heat of phase transition in the photoisomerization process of a series of azobenzene derivatives,the energy storage density of the azobenzene derivatives is greatly improved,and the problem of low energy storage density is solved.Using its photo-induced phase state conversion characteristics,it is combined with fabrics without solvation to prepare a flexible light-to-heat conversion film with certain mechanical strength.The supramolecular interaction（hydrogen bonding）formed between the azobenzene derivatives and the fabric greatly improves the stability of its cis conformation,thereby solving the problem of short energy storage life.The influence of alkyl chain structure on photophase conversion and photothermal conversion process of azobenzene derivatives is studied,and the structure-activity relationship is clarified,providing theoretical basis for the structural design of such photophase conversion azobenzene STF.Based on this,this paper has carried out the following three research work:（1）Design and synthesis of a series of azobenzene derivatives.Taking advantage of the difference in thermodynamic properties between the cis and trans conformations of azobenzene derivatives,a series of azobenzene derivatives with different alkyl chain structures are designed to realize solid/liquid two-phase photoisomerization in the process of photoisomerization.A series of azobenzene derivatives with photoinduced phase transition properties are synthesized by methods such as diazonium salt coupling and halogen substitution.Its molecular structure is determined by infrared spectroscopy（FT-IR）,nuclear magnetic resonance（~1H NMR）,mass spectrometry（MS）,elemental analysis（EA）,etc.（2）Study on the controllable phase transition and photothermal conversion properties of a series of azobenzene derivatives during photoisomerization.Using ultraviolet-visible absorption spectroscopy（UV-vis）to study the photo-induced cis-trans isomerization process and recycling performance of its solution.The photoisomerization process in the solid powder state is studied by hydrogen nuclear magnetic resonance（~1H NMR）,that is,the photothermal conversion efficiency and rate in practical applications.Differential scanning calorimetry（DSC）is used to study the energy storage density and energy storage half-life of its powder state,summarize the rules,and clarify the effect of different alkyl chain structures on its energy storage performance.（3）Preparation and properties of ready-to-use azophenyl photothermal conversion films.The IM-Azo flexible light-to-heat conversion film is prepared by combining the azobenzene derivatives（IM-Azo）with better energy storage properties with fabrics through photo-induced phase transition or thermal-induced liquefaction.The preparation process is simple and easy,no solvent treatment is required,and the environment is friendly;IM-Azo molecules are evenly distributed in the film,which is conducive to the effective penetration of ultraviolet light and helps to improve the charging rate;It is easy to form a supramolecular（hydrogen bond）interaction between the two,which improves the stability of the cis conformation IM-Azo and helps to improve the energy storage half-life of the film.The IM-Azo photothermal conversion film has better acid-base stability and flexibility,which can realize its application in more complex environments,and provide new ideas for the design of flexible wearable devices and environmentally friendly photothermal conversion devices.