Synthesis and electrochromic properties of trans-stilbene bearing copolymers obtained with different repeat unit and chain length

• Benzotriazole, thiophene and trans-stilbene were used to obtain random copolymers.
• Polymer chain length effect was examined via reaction times and feed ratio.
• Polymers show processability, multichromicity and fast switching times.

Three new random copolymers containing benzotriazole (BTz), thiophene (Th) and trans-stilbene (St) were synthesized via Stille coupling technique with different monomer ratios. In order to determine the effect of stilbene quantity on electrochromic properties of the polymers, feed ratios of the monomers were altered in chemical polymerization. Polymer chain length effect was also investigated via using different reaction times and the same feed ratio. The characteristics of the synthesized copolymers were compared based on their quantity of stilbene moiety and chain length. Redox potentials and HOMO/LUMO energy levels of all polymers were characterized by cyclic voltammetry. To evaluate the optical properties of the electrochromic copolymers, spectroelectrochemistry technique was used. Optical band gap values of the copolymers were found in the range between 1.85 and 2.06 eV. Optical contrasts and switching ability of the polymer films were determined by square wave chronoamperometry. Solution processable polymers reveal multichromicity upon oxidation and reduction at low potentials, fast switching times and low band gap.

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