Photo- and electrochemical properties of linked ferrocene and viologen donor-acceptor-type molecules and their application to electrochromic devices

This is a report on the electrochemical and optical properties of a new type of linked system of ferrocene (Fc) and viologen (V²⁺) units, Fc-(CH₂)₄-V²⁺-R (Fc-V²⁺). The cyclic voltammogram and absorption spectra have revealed that Fc and V²⁺ units are little effected by the nonconjugated bridge, -(CH₂) ₄-, since differences in electrochemical and optical properties between linked and nonlinked Fc and V²⁺ systems are not observed, in that both systems have similar redox and absorption characteristics. The linked Fc-V²⁺ system, however, showed higher UV resistance. Using Fc-V ²⁺ dye and a polymeric solid electrolyte (PSE), we succeeded in fabricating a large-area quasi-solid-state electrochromic cell (EC cell). This cell has shown excellent homogeneous coloration, and its EC properties can be explained in a simple graphical way based on the diffusion of redox species Fc-V⁺ and Fc⁺-V²⁺. Further, the EC cell fabricated with Fc-V²⁺ has shown excellent durability and was shown to be well-suited for all outdoor applications.