Study On Electrochemical Polymerization Of Triphenylamine Derivatives With The Introduction Of Electrochemical Active Groups And Electrochromic Properties Of Corresponding Polymers

Electrochromic phenomenon and electrochromic materials have attracted much attention due to their unique properties.Among them,conductive polymer-electrochromic materials have arised more interest among many electrochromic materials because of their various kinds,plenty color,high contrast,good processing performance,controllable energy band and fast response speed.Polytriphenylamine and its derivatives have become the research hotspot of electrochromic materials.However,a large number of previous studies have shown that it is difficult for traditional triphenylamine derivatives to obtain polymer films by electrochemical polymerization.In this paper,electron donor groups with different electrochemical redox activity were introduced into triphenylamine（TPA）to study their effects on the electrochemical properties and electrochemical polymerization process of triphenylamine,and then to study their effects on the electrochromic properties of polymer films.In the first part of this paper,three TPA derivatives.N,N-dipheny-l-4-（thiophene-2-yl）-aniline（TPATH）,N,N-diphenyl-4-（5-methylthiophene-2-yl）-anili ne（TPATHM）,N,N-diphenyl-4-（thiophene-3-yl）aniline（DPTA）,were designed and synthesized by introducing thiophene groups into the para-position of triphenylamine.The electrochemistry of the three monomers was studied by cyclic voltammetry.It was found that TPATH and TPATHM could not be electrochemically polymerized,while DPTA could be electrochemically polymerized,which indicated that the electrochemical polymerization was carried out simultaneously on thiophene and triphenylamine.Ultraviolet-visible spectroscopy analysis showed that PDPTA polymer films exhibited obvious absorption peaks at 354,485 and 770 nm,respectively.Spectroelectrochemical analysis showed that PDPTA polymer films exhibited color changes from light yellow-green to light blue,with optical contrast of39.64%in the visible region,response time of 4.72 s（colored time）,2.68 s（bleached time）,optical contrast of 33.94%at 1100 nm in the near infrared region,response time of 4.33 s（colored time）,and 3.64 s（bleached time）.In the second part,the pyrrole group was introduced into the para-position of triphenylamine,and two monomers N,N-diphenyl-4-（1H-pyrrole-1-yl）aniline（DPPA）,N,N-diphenyl-4-（2,5-dimethyl-1H-pyrrole-1-yl）aniline（DPPAM）were designed and synthesized.The electrochemical properties and electrochemical polymerization process of the two monomers were studied by cyclic voltammetry.It was found that with the increase of scanning cycles,the peak current intensity increased gradually,indicating that the corresponding polymer was formed in the process,indicating that triphenylamine derivatives could be electrochemically polymerized.The scanning electron microscopy data show that PDPPAM film presents loose spherical particles with a diameter of about 230 nm.Spectroelectrochemical measurements show that PDPPAM has good electrochromic performance and can realize reversible color changes.At the same time,PDPPAM has relatively high optical contrast of 35.90%at 720 nm and 13.42%at 1100nm.Meanwhile,fast response time of 1.55 s（colored time）,1.15 s（bleached time）at 720nm and 0.72 s（colored time）and 0.98 s（bleached time）at 1100 nm.In the third part,A novel triphenylamine（TPA）derivative（（E）-N-（4-（Diphenylamino）phenyl）-formimidoylferrocene）（TPAFc）containing ferrocene（Fc）unit was designed and synthesized successfully.Theoretical calculation and experimental data show TPAFc possessess higher HOMO energy level and the lower onset oxidative potential compared to TPA monomer.Cyclic voltammetry test demonstrates cross-linking between TPA units and the formation of an electroactive polymer film during successive scans.This intriguing phenomenon may be ascribed to the two-step redox process:the pre-oxidation behavior of Fc unit promotes TPA units to occur oxidation reaction and stabilize cationic radicals during the electrochemical process.SEM images indicate PTPAFc film shows the surface morphology of uniform tubular structures,which may largely increase the contact area between the polymer film and the electrolyte solution.Interestingly,PTPAFc film exhibits reversible multicolor changes switched from neutral transparent color to light orange and blue in fully oxidized state,which are attributed to that the existence of Fc unit brings out multiple redox states.In addition,the polymer film presents excellent electrochromic properties in term of high optical contrast（58.85%）,good coloration efficiency(about 170 cm²?C^-1)and fast switching time（about 2 s）.In view of these excellent features,the developed PTPA derivative is very satisfactory for applications on high-performance electrochromic devices.