Neutral state colorless electrochromic polymer networks: Spacer effect on electrochromic performance

A series of carbazole-based monomers and their corresponding polymers with various spacer units were synthesized and coated onto ITO-glass surface via an electrochemical cross-linking process. All carbazole-based polymers exhibited multi-electrochromic behavior thanks to two separate oxidation processes. All materials were characterized by FT-IR, ¹H NMR, GPC, DSC, UV-vis, Florescence and CV. In addition, electrochromic properties of the cross-linked polymer films were investigated via spectro-electrochemical measurements. The colorless films were converted to yellowish green and greenish blue colors at the anodic regime. The results indicate that the spacer unit between the carbazole unit and the polymer backbone has a great impact on the optical and electrochemical properties and also on the electrochromic performance of these polymers. PVBEC with benzyloxy based spacer exhibits a high contrast ratio (ΔT% = 55 at 690 nm), a faster response time of about 2.1 s, a higher coloration efficiency (331 cm² C^-1) and a better stability (retains its performance by 94.3% even after 1000 cycles).