Synthesis Of Triphenylamine Derivatives And Their Application In Electrochromic Composite Devices

Electrochromism refers to a phenomenon in which an electroactive material undergoes changes in optical properties driven by an external voltage.In recent years,electrochromic materials have received extensive attention.It has good application prospects in the fields of smart windows for energy-saving buildings,anti-glare rearview mirrors for automobiles,information displays,and electrochromic electronic skins.The propeller-shaped triphenylamine（TPA）molecule is a good hole transport material,which is mainly due to its own remarkable photoelectric activity.In this paper,the author synthesized three TPA derivatives:N,N′-di（4-（（3-（triethoxysilyl）propyl）imino）methyl）phenyl-N,N′-diphenyl-4,4′-biphenyl-diamine（TPB-PSSO）,4-（（4’-（dipheny-lamino）-[1,1’-biphenyl]-4yl）（phenyl）amino）benzaldehyde（TPB-CHO）,and N,N,N′,N′-Tetrakis（4-bromophenyl）benzidine（TPB-4Br）using Fourier transform infrared spectroscopy（FTIR）,proton nuclear magnetic resonance spectroscopy（¹H NMR）,carbon nuclear magnetic resonance spectroscopy(¹³C NMR),silicon nuclear magnetic resonance spectroscopy(²⁹Si NMR)and mass spectrometry（MS）.These several characterization methods were used to confirm the structure of the three synthesized target molecules.The corresponding molecular structures are as follows:（?）The author also used ultraviolet-visible light（UV-vis）spectrometer and electrochemical workstation to explore the optical and electrical properties of the three TPA derivatives.The results show that these three TPA derivatives have good electrochemical redox activity,and the maximum absorption peaks of the three target molecules are concentrated in the 200-400 nm wavelength range.The author used these three TPA derivatives as active materials,and assembled them into electrochromic devices:ITO/triphenylamine derivatives gel electrolyte/ITO.In addition,WO₃film was introduced into the electrochromic device,and the corresponding electrochromic composite device was prepared.The device structure is:ITO/WO₃/triphenylamine derivatives gel electrolyte/ITO.The electrochromic performance of the device is studied,and the results are as follows:（1）Electrochromic devices（the substrate is ITO glass）based on TPA derivatives and their composite devices:TPB-PSSO,TPB-CHO,and TPB-4Br are respectively formulated into electrochromic gel electrolytes,and assembled electrochromic devices:ECD 1（ITO/TPB-PSSO gel electrolyte/ITO）,ECD 2（ITO/TPB-CHO gel electrolyte/ITO）,and ECD 3（ITO/TPB-4Br gel electrolyte/ITO）.Through electrodeposition technology,another layer of WO₃ film was inserted into the above-mentioned devices to prepare the corresponding electrochromic composite devices:ECD 4（ITO/WO₃ film/TPB-PSSO gel electrolyte/ITO）,ECD 5（ITO/WO₃film/TPB-CHO gel electrolyte/ITO）,and ECD 6（ITO/WO₃ film/TPB-4Br gel electrolyte/ITO）.Through the electrochromic performance test,it can be found that ECD 1 can achieve a reversible transition between gray and light yellow upon alternately applying+1.9 V and 0.0 V voltage,ECD 2 can achieve a reversible transition between dark green and yellow upon alternately applying+2.5 V and 0.0 V voltage,and ECD 3 can achieve a reversible transition between cyan and light yellow upon alternately applying+1.6 V and 0.0 V voltage.Besides,ECD 4 can realize the reversible transition from blue to light yellow and then to gray upon alternately applying-2.8 V、0.0 V（or+0.6 V）and+2.8 V voltage,ECD 5 can realize the reversible transition from black to yellow and then to dark green upon alternately applying-1.9V、0.0 V（or+0.7 V）and+2.5 V voltage,and ECD 6 can realize the reversible transition from dark green to light yellow and then to unevenly colored cyan upon alternately applying-1.9 V、0.0 V and+1.9 V voltage.ECD 2 has the highest optical contrast,and its optical contrast at 484nm is 42.2%.Compared with devices without WO₃ film,the optical contrast of composite electrochromic devices has been improved.Especially ECD 5,its optical contrast at 496 nm reaches 51.0%.The response time of ECD 1 and its corresponding composite device ECD 4has reached the millisecond level that are 9 ms（t_c）/5 ms（t_b）and 4 ms（t_c）/5 ms（t_b）,respectively,and the cycle stability is relatively good.Besides,the coloring efficiency of ECD 2 and its corresponding composite device ECD 5 are relatively excellent.The maximum coloring efficiency is 138 cm²/C and 312 cm²/C,respectively.（2）Flexible electrochromic devices（the substrate is PET coated with ITO）based on TPA derivatives and their flexible composite devices:the TPA derivatives TPB-PSSO,TPB-CHO and TPB-4Br were respectively dissolved into a Li Cl O₄ solution.Then these solutions were respectively mixed with a photocurable resin in a certain volume ratio,and a small amount of photoinitiator is added.Finally,the above solution was injected into the container assembled by the PET-ITO flexible substrate,and then the devices were prepared into the flexible electrochromic devices:ECD 7（PET-ITO/TPB-PSSO photo-curing electrolyte/PET-ITO）,ECD 8（PET-ITO/TPB-CHO photo-curing electrolyte/PET-ITO）and ECD 9（PET-ITO/TPB-4Br photo-curing electrolyte/PET-ITO）by photo-curing technology.By means of physical vapor deposition technology,another layer of WO₃ film was inserted into the above-mentioned devices,and the corresponding electrochromic flexible composite electrochromic devices:ECD10（PET-ITO/WO₃ film/TPB-PSSO photocurable electrolyte/PET-ITO）,ECD 11（PET-ITO/WO₃ film/TPB-CHO photocurable electrolyte/PET-ITO）and ECD 12（PET-ITO/WO₃film/TPB-4Br photocurable electrolyte/PET-ITO）are prepared.Through the electrochromic performance test,it can be found that ECD 7 can achieve a reversible transition between green and dark yellow upon alternately applying+2.6 V and 0.0 V（or-0.5 V）voltage,ECD 8 can achieve a reversible transition between black and yellow upon alternately applying+2.8 V and0.0 V（or-0.6 V）voltage,and ECD 9 can achieve a reversible transition between gray and light yellow upon alternately applying+3.9 V and 0.0 V（-0.5 V）voltage.ECD 10 can realize a reversible transition from colored dark green to dark yellow and then to dark green upon alternately applying+2.6 V,0.0 V and-1.5 V voltage,ECD 11 can realize from colored yellowish brown to yellow and then to dark black upon alternately applying+3.0 V,0.0 V and-1.7 V voltage,and ECD 12 can realize the reversible transformation from yellowish brown to light yellow and then to blue upon alternately applying+3.9 V,0.0 V and-2.5 V voltage.ECD8 has the highest optical contrast,and its optical contrast in the 500-800 nm wavelength range exceeds 70.0%.Compared with flexible electrochromic devices without WO₃ film,while applying negative potential to flexible composite electrochromic devices,the optical contrast of flexible composite electrochromic devices has been significantly improved,and the maximum optical contrast of ECD 10,ECD 11,and ECD 12 are 83.7%,82.7%,and 62.5%,respectively.Therefore,flexible composite electrochromic devices have both flexibility and high optical contrast features.From the perspective of stability,a comprehensive comparison of flexible electrochromic devices and their flexible composite electrochromic devices can be seen that ECD 9 still retains 78.7%of the initial doped（or dedoped）charge after 400 cycles of testing,showing a good cycle stability.From the perspective of coloring efficiency,ECD 8 has the highest coloring efficiency.The maximum coloring efficiency is 736 cm²/C.