NEW EDOT CONTAINING POLYMERS: EFFECT OF RING SIZE ON THE BENZIMIDAZOLE ACCEPTOR

• Effect of ring size on the benzimidazole acceptor unit was investigated.
• Novel monomers based on Benzimidazole and EDOT were synthesized.
• Electrochromic polymers through electrochemical polymerization of monomers were obtained.
• Electrochemically obtained polymer showed both p- and n-doping behaviors.

In this study, three different benzimidazole (BIm) based acceptor groups bearing cyclohexane, cycloheptane and cyclooctane rings at 2-C position of benzimidazole were synthesized and coupled with ethylenedioxythiophene (EDOT) donor units via Stille cross-coupling reaction. The resulting donor-acceptor-donor (DAD) type monomers were examined in terms of their electrochemical and optical behaviors. All three monomers exhibited dual absorption bands due to their donor-acceptor pattern and exhibited one irreversible oxidation peak at about 0.80 V. The monomers were electrochemically polymerized via both potentiostatic and potentiodynamic methods and electro-optical properties of obtained conjugated polymer films were investigated in monomer free electrolytic solution. It was found that the polymer films exhibited quasi-reversible redox behavior due to the doping/dedoping process of the polymers, which was accompanied by a reversible electrochromic behavior. Electrochromic investigations showed that all three polymer films showed similar multichromic behaviors: green in the neutral state, gray in the oxidized state, and brick-red in the reduced state. Their band gap (Eg) values were elucidated utilizing spectroelectrochemical data and it was found to be around 1.18 eV. Furthermore, one of the polymer film was utilized for the construction of transmissive type electrochromic device (ECD) with poly(3,4-ethylenedioxythiophene) (PEDOT).