Preparation Of Triphenylamine Covalent Organic Frame (COFs) Thin Films And Their Electrochromic Properties

Electrochromism refers to the redox reaction of the material under the action of applied voltage,which changes the transmittance or reflectance of light,and the macroscopic performance is the change of color and transparency.Organic electrochromic materials are widely concerned due to their rich color changes,high coloring efficiency,and easy modification.Triphenylamine is widely used as electrochromic materials because of its low oxidation potential,fast reaction speed,high color contrast,and good thermal stability.Covalent Organic Frameworks(COFs)is a class of materials with low density,large specific surface area,adjustable size and structure formed by covalent bonding.The porosity,crystallinity,? electron conjugation system and ordered ?-? stacking between layers can effectively promote the conduction of electrons and the transport of ions,so COFs materials have potential applications in the field of optoelectronics Value,it is reported that COFs thin films have not yet been used in the field of electrochromism.In this paper,we used(Tris(4-aminophenyl)amine,TAP A),(4-Formylphenylfr)Amine,TFPA),(2,4,6-Trihydroxy,1,3,5-Benzenetricarboxaldehyde,THBT)and 1,3,5-Benzenetricarboxaldehyde,BT)as building block to successfully prepared three electrochromic films of TATF-COFs,TATH-COFs and TABT-COFs on ITO glass modified with 1,6-hexanediamine.The regular pore structure of COFs can not only expose more active sites of triphenylamine to the electrolyte,but also accelerate the electrolyte transport.The?-electron conjugated system and the inter-layer ?-? stacking effectively promote the electron transport in COFs in two and three directions,and improve the electrochromic properties of triphenylamine.The electrochromic properties of the three COFs films were thoroughly studied by cyclic voltammetry,response speed and optical contrast,and the formation mechanism of COFs was analyzed by scanning electron microscopy(SEM).The electrochromic test results show that the TATF-COFs film can realize the color conversion between bright yellow and magenta,The coloring time and fading time are 4.5 s and 4.9 s,respectively,and the coloring efficiency is 115 cm2·C-1.TATH-COFs can change from dark yellow to light cyan,its coloring time and fading time are 3.2 s and 5.2 s,respectively,the coloring efficiency is 125.1 cm2·C-1,TABT-COFs film can change from light yellow to light blue,its coloring time and fading time are 3.5 s and 5.6 s,respectively,and the coloring efficiency was 110.6 cm2·C-1.Compared with other triphenylamine derivative materials,TATF-COFs,TATH-COFs,TABT-COFs three kinds of COFs film has multi-color electrochromic performance,fast response time,high coloring efficiency,good cycle stability and other advantages.The reversible reaction of dynamic imine bonds during the solvothermal process induced the microscopic morphology of TATF-COFs,TAHT-COFs,TABT-COFs from nanoparticles to self-assembled into nanofibers,and from coral-like self-assembled into nanomicrospheres,Self-assembly from nanoparticles into nanospheres.In this paper,we first verify the possibility of electrochromism of COFs materials.Considering that a large number of building units have redox properties,it is expected that COFs-based electrochromic materials will have rich color changes and other novel properties.