Redox-Switchable Bis-fused Tetrathiafulvalene Analogue: Observation and Control of Two Different Reduction Processes from Dication to Neutral State.

Derivatives of a new bis-fused donor composed of TTF and extended TTF with an anthraquinoid spacer (TTFAQ) (2) were successfully synthesized. X-ray structure analysis of the tetrakis(methylthio) derivative 2Aa and its I3- salt revealed that the TTFAQ moieties of both 2Aa and 2Aa•+ adopt the so-called saddle conformation similar to most neutral TTFAQs. The results obtained from the X-ray structure analysis and cyclic voltammetry suggest that a positive charge in 2Aa•+ is unevenly distributed on the TTF moiety, while both positive charges of 22+ are mainly located on the TTFAQ moiety. In the first two-electron redox processes, an extra cathodic wave attributed to the coexistence of a different reduction process from the oxidation process was observed for most of the derivatives.