Synthesis, and optical and electrochemical properties of germanium-bridged viologen

Abstract

A Ge-bridged methylviologen derivative (GMV2+2I-) was synthesized by dimethylation of dipyridinogermole (DPyG). Viologen GMV2+2I- showed a UV absorption band at 270 nm, similar to DPyG and longer than the corresponding bridge-free methylviologen (MV2+2I-). Electrochemical properties of GMV2+2I- were investigated with respect to cyclic voltammograms, showing highly reversible two step reduction, like MV2+2I-. Interestingly, GMV2+2I- exhibited enhanced electron-affinity with higher 1st reduction potential by approximately 0.08 V than that of MV2+2I-, likely due to the effects Ge-bridge lowering the LUMO energy level. However, the 2nd potential was little affected by the bridge. Clear electrochromic colour changes based on the reversible electrochemical interconversion among GMV2+/GMV+/GMV were observed in acetonitrile. Monomethylated DPyG (GMV′+I-) was also prepared, whose properties are discussed in comparison with those of DPyG and GMV2+2I-.