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−V2+ 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.