High-performance D–π–A–π–D type electrochromic polymers based on nitro-substituted triphenylamine derivatives with thiophene and EDOT as π bridges

Abstract

π-Bridges play an important role in tuning molecular properties including molecular configuration, optical absorption, initial oxidation potential, charge transport and film morphology. Herein, two novel donor(D)–π–acceptor(A)–π–donor(D) type conjugated monomers ETTPA and EETPA were designed and synthesized using thiophene and EDOT units as π-bridges. Both ETTPA and EETPA exhibited red-shifted absorption spectra and better electrochemical stability compared to TTPA without the π-bridge. In particular, ETTPA had a much lower initial oxidation potential of 0.23 V than its counterpart EETPA due to the smaller steric hindrance of thiophene than that of EDOT as the π-bridge. In addition, the corresponding polymer PETTPA exhibited a reversible and stable color change from dark brown to dark blue between the neutral and oxidized states with a favorable optical contrast of 41% in the near infrared region at 1100 nm, a high coloration efficiency of 332.6 cm² C⁻¹ with an extremely fast response time as low as 0.3 seconds, and a promising optical memory behavior. These results demonstrated that embedding the π-bridge between the D unit and A unit can optimize the optoelectronic properties of D–A–D type conjugated polymers, facilitating the design and development of high-performance electrochromic polymers.