Benzotriazole-EDOT electrochromic conjugated polymers show sub-second response time and 774 cm2 C−1 coloration efficiency

Abstract

To investigate the effect of double fluorine substitution on the optical, electrochemical, thermodynamic, morphological and electrochromic properties of electrochromic polymers, two benzotriazole-EDOT electrochromic conjugated polymers PBTz-E and P2F-BTz-E were synthesized via direct (hetero)arylation polymerization (DHAP). P2F-BTz-E was obtained after fluorination of PBTz-E by substituting two hydrogen atoms on the benzotriazole unit with two fluorine atoms. Both polymers exhibited similar purple colors in the neutral state, and the polymer films reversibly and stably switched between neutral and oxidized states with minimal degradation over 1000 s. The optical contrast, response time and electrochemical stability of P2F-BTz-E are significantly improved, and the reduction time can reach sub-second speed (0.5 s). However, the severe stacking and aggregation of fluorinated polymer P2F-BTz-E resulted in unsatisfactory film surface morphology and low coloration efficiency. Surprisingly, PBTz-E shows magnificent coloration efficiency (774 cm² C⁻¹ at 570 nm) because of the low transfer charge. Flexible ECDs prepared from two polymers demonstrated good reversible electrochromic properties. These results provide valuable information for the elaboration of high-performance electrochromic polymers based on benzotriazole.