Donor-π-bridge-acceptor type polymeric materials with pendant electron-withdrawing groups for electrochromic applications

• Donor-π-bridge-acceptor copolymers with different electrophilic groups were synthesized.
• Electrochromic devices composed of PBDTTPAs layers, as the working electrode, and vanadium pentoxide, as the counter electrode, were fabricated and evaluated.
• The PBDTTPA-CHO film and device show multicolor electrochromic behavior which exhibited vivid yellow, green, and gray with better electrochromic performance than PBDTTPA-COOH.

A novel donor-π-bridge-acceptor copolymer, PBDTTPA-CHO, containing 4-(Bis(4-bromophenyl)-amino)benzaldehyde (TPA-CHO) and 4,8-bis-(2-ethyl- hexyloxy)-oxybenzo-[1,2-b:3,4-b’]dithiophene (BDT), was successfully synthesized using Stille coupling polymerization, and the pendant aldehyde group was modified with cyanoacetic acid to synthesize another polymer, PBDTTPA-COOH. Each of these new polymers are soluble in organic solvents and can be cast onto rigid or flexible substrates. The polymers with different electrophilic groups exhibit different electrochromic behaviors, including different colors, driving voltages and transmittances. The polymer film of PBDTTPA-CHO manifests reversible electrochemical oxidation and reduction accompanied by multicolor changes from its yellow neutral state to a highly absorbent green semi-oxidized state and a gray fully oxidized state, its transmittance change at 601 nm is 43%. PBDTTPA-COOH switches between orange and light green. We fabricated and evaluated electrochromic devices using a PBDTTPA layer as the working electrode and vanadium pentoxide as the counter electrode. With the contribution of counter electrodes, devices of both polymers show similar color changes but higher transmittance than their films.

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