Flexible Triazolopyridines-Based D-A-D Electrochromic Materials And Devices

Donor-acceptor-donor?D-A-D?type conjugated polymers,an important class of organic electrochromic materials,have been extensively exploited due to their flexibility of color modification,superior optical contrast ratios,high coloration efficiency and stability.Albeit several advances in both material development and device fabrication and application,the rational design of high-performance electrochromic conjugated polymers and the patterning of flexible electrochromic display devices remains a key issue in the development of this field.Previous studies of D-A-D type conjugated polymers mainly focused on the modification of donors,and there are few researches on receptors.The relationship between receptors and performances is still unclear,which need further study.Triazolopyridine has stronger electron-withdrawing ability,and its N atom can be easily modified and functionalized,which can be used as superior acceptors.In this work,by the employment of alkyl substituted[1,2,3]triazolo[4,5-c]pyridines?PTzs?as acceptors and thiophenes?Ths?as donors,we successfully obtained ten novel triazolopyridines-based D-A-D type electrochromic materials via Stille coupling and electropolymerized to obtain the corresponding polymers.The effects of donors and alkyl side chains of acceptors for the properties of precursors and polymers have been systematically investigated,and the superior polymer electrochromic materials with high contrast,high coloring efficiency,fast response speed and high stability have also been obtained.We further explore the fabrication of flexible and patterned electrochromic devices based on these superior polymers under optimized conditions,and study detailedly the electrochemical and electrochromic performances of these devives upon both doping-dedoping process and bending in the nature light and near-infrared light.The specific research contents and results as follows:1.By the employment of alkyl substituted[1,2,3]triazolo[4,5-c]pyridines?PTzs?as acceptors and thiophene?Th?as donor,two D-A-D type polythiophene-based electrochromic precursors have been designed and synthesized.These precursors display low the oxidation onset potentials?1.21/1.25V?.Albeit the electropolymerized polymers reveal excellent adhesion on the working electrode,the electrochemical stability is still inferior?only remain 43%electrochemical activity after 100 cycles?.Owing to the?-?/?-?couping reaction of thiophene ring during the electrochemical polymerization,these polymers display no obvious color change in the whole spectral range?visible region and near-infrared region?and low optical contrast?only up to 13%?,which is not benefit for electrochromic applications.2.The introduction of alkylthiophene donors reduces the structural defects and effectively improves the electrochemical stability and electrochromic properties of these D-A-D type electrochromic polymers.By the employment of alkyl substituted[1,2,3]triazolo[4,5-c]pyridines?PTzs?as acceptors and alkyl thiophenes?Ths?as donors,six D-A-D type electrochromic precursors have been synthesized and electropolymerized to obtaion their corresponding polymers.The introduction of alky chains further reduce the oxidation onset potentials?1.09-1.15 V?and effectively improve the electrochemical activity and stability?the electrochemical activity remains 86%after 1000 cycles?.Meanwhile,the introduction of alky chains reduce the bandgap?1.18-1.90 eV?and improve the electrochromic properties.These polymers display obvious and reversible color change,high optical contrast up to88%,high coloring efficiency(1397 cm² C^-1).However,the electrochemical stability of these polymers is lower and the response time is longer.3.The triazolopyridine-EDOT electrochromic precursors have been synthesized.And the stronger electron donating ability of EDOT further improve the stability of these corresponding polymers and reduce the response time.In order to further reduce the bandgap to enhance its stability and electrochromic properties,two triazolopyridine-EDOT precursors have been designed and synthesized by the employment of stronger electron EDOT unit.These precursors reveal lower the oxidation onset potentials?0.94 V/0.98 V?,which is benefit for the obtainment of high-quality polymer films.It is found that the introduction of EDOT unit significantly improved the redox stability of these polymers,and the electrochemical activity of the polymer remained above 97%after 5000 cycles.The optical bandgap of these polymers was further reduced to 121 eV/1.15 ev.Compared with the pyridine alkylthiophenes-based D-A-D type electrochromic materials,these materials maintain high optical contrast?81%?and coloring efficiency(1298 cm² C^-1)and further improve the electrochemical stability and reduce the response time?less than 1 s?.4.The fabraction of flexible and patterned electrochromic devicces based these superior materials.We explore the fabraction of these devices upon optimized conditions,with P?3MTh-HPTz?as electrochromic functional layer,ITO-PET as working electrode and counter electrode and gel electrolyte as supporting electrolyte,and the patterns are obtained by electrochemical polymerization.These devices display a reversible color change from purple to blue upon bending.Moreover,these devices can be used to mimic color-changing process in smart display,and camofludge under NIR imaging.