Synthesis And Electrochromic Properties Of Poly(Ether Sulfone)s Containing Triphenylamine Structure

Electrochromism generally refers to materials whose color changes reversibly under the action of an external electric field.Since Platt discovered the EC phenomenon in 1961 and Deb published the first"sandwich-type"electrochromic device(ECD)made of amorphous WO₃ film in 1969,EC technology has been booming ever since.After years of development,a variety of EC materials have been developed,mainly including metal oxides,coordination compounds,organic small molecules and polymers.After years of development,a variety of EC materials have been developed,mainly including metal oxides,coordination compounds,organic small molecules and polymers.At present,a large number of electrochromic materials have entered people's lives,such as color-changing glasses,smart windows,displays,and adaptive dynamic camouflage.In recent years,electrochromic polymers(ECPs)have received widespread attention due to their low power consumption,easy color adjustment through molecular design,high flexibility and solution processability.Non-conjugated high-performance polymers(polyimide,polyamide,poly(aryl ether sulfone),etc.)with the structural characteristics of special engineering plastics have been rapidly developed in the optoelectronic field due to their excellent thermal stability,film formation and solubility.In addition,due to the low degree of conjugation,these materials are almost transparent in the neutral state.However,the high oxidation potential and poor cycle stability limit the further application of non-conjugated polymers as optoelectronic materials.Therefore,designing polymer materials with low oxidation potential and high cycle stability through structure has important research value.Based on the work within the group,we introduced triphenylamine groups as color-changing units and electron donors into the poly(aryl ether sulfone),designed and synthesized a series of bifunctional poly(aryl ether sulfone)materials containing triphenylamine structure,and systematically study its electrochromic and storage properties.The research work of this paper mainly includes the following two parts:1.According to the design idea of the donor-acceptor structure,a series of triphenylamine-based poly(aryl ether sulfone)containing different acceptor units in the side chain were synthesized.The electrochemical test structure showed that the method of constructing a donor-acceptor structure in the side chain structure of poly(aryl ether sulfone)effectively reduced the onset potential of the polymers.At the same time,these polymers all had electrochromic properties.The results showed that PES-TPAs all exhibit fast color switching speed(the switching time is within 7s),and good cycle stability(52 cycles).These results proved that it is feasible for non-conjugated polymers to improve the photoelectric behavior of materials by constructing side chain D-A structures.2.According to the design idea of expanding the conjugation degree of the donor,a poly(aryl ether sulfone)material based on triphenylamine(without 4-substituted)was synthesized.PES-TPA-H underwent electrochemical cross-linking during the electrochemical test,which expanded the degree of donor conjugation.Two pairs of reversible redox peaks appeared in the cyclic voltammetry curve,which proved that PES-TPA-H was electrochemically cross-linked during the test to form a TPB structure.Because the TPB structure had a stronger ability to donate electrons,the onset potential of the material was significantly reduced and the mechanism of cross-linking was analyzed in detail.PES-TPA-H film realized the color switching from colorless to yellow to blue.By reducing the scanning potential to reduce electrochemical side reactions,the electrochromic cycle stability of the PES-TPA-H polymer film was greatly improved.By comparing the electrochromic performance of different film thicknesses,the polymer film with a film thickness of 200±30 nm had the best electrochromic performance.