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Abstract
Three solution-processable D-A-type conjugated polymers P1, P2 and P3 were successfully synthesized via the Pd-catalyzed Stille cross-coupling copolymerization approach, with 6,8-Dibromo-3,3-bis-decyl-3,4-dihydro-2H-thieno[3,4-b][1,4] dioxepine (M1) and 2,5-Bis(trimethylstannanyl)thiophene (M3) as the donor units and 4,7-Dibromo-5,6-difluoro-2-(2-hexyl-decyl)-2H-benzotriazole (M2) as the acceptor unit, wherein the feed ratio of the three units was 1:3:4 (M1:M2:M3, the same below), 1:1:2 and 3:1:4 for P1, P2, and P3, respectively. The results obtained by our test showed that the feed ratio between the D and A units had a significant effect on both the electrochemical and the spectroelectrochemical properties of the three polymers. The copolymers exhibited a gradually deepening red color in neutral state with the increase of M1 content and then turned to a transmissive grey color in the oxidation state. Also, three copolymers showed good performance in electrochromic parameters, which mainly consists of optical contrast, response time, and coloration efficiency. In general, the excellent electrochromic performances of the copolymers make them outstanding candidates for electrochromic material applications.
Highlights
Since the first conductive polymer-doped polyacetylene was discovered in the 1970s [1,2], research in conductive polymers has not stopped and mainly includes thiophene [3,4], furan [5], pyrrole [6], and their derivatives
ProDOT-decyl2 was synthesized according to the previous literature [33], and the synthetic route is shown in Scheme 1. 11.5 mmol of diethyl malonate was added dropwise to a mixed solution containing 35 mmol of 1-bromododecane, 35 mmol of sodium hydride, and 200 mL of anhydrous tetrahydrofuran, and the mixture was stirred under reflux for 24 h under an argon atmosphere
According to the experimental data mentioned above, all of the three copolymers have high molecular weights and low PDI values, which might favor the electrochemical stabilities of the polymers in several aspects, including the improvement of the adhesion to the substrate, the resistant to the dissolve in the supporting electrolyte, and the maintenance of a high optical contrast after repeated electrochromic switches [35]
Summary
Since the first conductive polymer-doped polyacetylene was discovered in the 1970s [1,2], research in conductive polymers has not stopped and mainly includes thiophene [3,4], furan [5], pyrrole [6], and their derivatives. The introduction of the alkyl side chain at position 1 increases the solubility of the synthetic polymer, which makes the FBTA a good candidate for the preparation of Ecps as the acceptor units [28]. A few of D-A type conjugated polymers have been designed and synthesized based on FBTA as the acceptor unit, and the corresponding donor units included benzodithiophene (BDT) [29], benzo[1,2-b:4,5-b0 ]dithiophene (BDTT) [30], BDTT with octylthio chains [30], 3-hexylthiophene [31], terthiophene and quaterthiophene [28]. The studies on the application of the above resulting copolymers are mainly focused on the field of bulk heterojunction (BHJ) solar cells and field effect transistors Of these devices, the FBTA containing polymers showed excellent performance. The results showed that the increase of M1 content is beneficial to the electrochromic properties of the polymers, while the M2 is just the opposite, which is the main contribution of the present work
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