Fast Switching Properties and Ion Diffusion Behavior of Polytriphenylamine Derivative with Pendent Ionic Liquid Unit.

A novel triphenylamine derivative linked ionic liquid unit TTPACIL-BF was designed and synthesized successfully, and its corresponding polymer PTTPACIL-BF was obtained by electropolymerization method. TTPACIL-BF exhibits higher HOMO energy band and lower onset oxidative potential compared to TTPACBr without modifying ionic liquid unit. Both PTTPACIL-BF and PTTPACBr show similar color change and optical contrast under different redox states. However, PTTPACIL-BF presents faster electrochromic switching time than that of PTTPACBr owing to the improved ionic conductivity and ion diffusion coefficient with the introduction of pendent ionic liquid unit. It is more intriguing that PTTPACIL-BF could show electrochromism under different potentials even without supplying any additional electrolyte. The particular behavior further proves that BF- ions around imidazole cations at the side chain may participate in balancing the charge of the polymer backbone when redox reaction happens, resulting in faster movement of ions during the doping process. The results imply that introducing ionic liquid unit to the side chain is an efficient method to improve switching time of conjugated polymers and would be inspirational for design and preparation of novel bifunctional electrochromic polymeric electrolytes.