Synthesis, electrochemistry and electrochromic properties of donor-acceptor conjugated polymers based on swivel-cruciform monomers with different central cores

Two swivel-cruciform D-A conjugated monomers (BTBBT and BTDQL) combining 5,5′-bibenzo[c] (Lv et al., 2017; Higginbotham et al., 2018; Dai et al., 2017) [1,2,5]thiadiazole (BBT) and 2,2′,3,3′-tetramethyl-6,6′-biquinoxaline (DQL) as the A units and 2,2′-bithiophene (BT) as the D unit are synthesized. The corresponding polymer films (pBTBBT and pBTDQL) are smoothly obtained on ITO-glass via electrochemical polymerization. Owing to the structural similarity, BTBBT and BTDQL enable to be electropolymerized under the same conditions, resulting in the similar thickness and surface morphology of their corresponding polymer films. Interestingly, pBTDQL displays the coloration time of 0.9 s at λ max and 0.5 s at 900 nm, which is much shorter than that of pBTBBT with the coloration time of 6.3 s at λ max and 3.0 s at 900 nm under the same conditions. The obviously rapider electrochromic switching rate of pBTDQL is attributed to its lower oxidation potentials and higher redox charge as evidenced by cyclic voltammetry results, which indicate an easier and more charge injection during electrochemical process. The electrochemical impedance spectroscopy results further demonstrate that pBTDQL exhibits the lower charge-transfer resistance and ion-diffusion resistance. These data indicate that charge transport property of conjugated polymer plays a key role on the electrochromic switching rate of pBTBBT and pBTDQL, and additionally DQL could serve as an electron-accepting building block for the constructions of faster switching conjugated polymer-based electrochromic materials. • Two D-A conjugated polymers based on swivel-cruciform monomers with different A cores were synthesized by electrochemical polymerization. • PBTDQL exhibited the obviously rapider electrochromic switching rate than pBTBBT, which was attributed to the lower charge-transfer resistance and faster ion-diffusion behavior. • The charge transport processes play key roles on the switching rate of electrochromic conjugated polymers.