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

Abstract

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 I 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 2 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.

Periphery Modification of Tetrathiafulvalenes: Recent Development and Applications

“…In sharp contrast, the two‐electron transfer processes of 20 and 21 were irreversible at a scan rate of 50 mV s −1 (Figure 14). Although these results are very similar to those reported for TTFAQ derivatives with TTF moieties, this is the first time that two different reduction processes for TTFAQ derivatives without TTF moieties have been observed using cyclic voltammetry [2h,29b] . Based on these results, we propose the emergence of two reduction processes.…”

Synthesis, Structures, and Electrochemical Properties of Bis‐ and Tetrakis(diphenylphosphino)tetrathiafulvalenes Extended with an Anthraquinoid Spacer

“…The simultaneous two‐electron transfer processes of 1 and 2 are irreversible, and the reversibility of these redox waves is enhanced when the voltammetry is carried out at a lower scan rate of 1 mV/s. These results are very similar to those reported for TTPAQ and TTPY‐1‐AQ, [5b,c] demonstrating that two different reduction processes depending on the scan rate can also be observed for TTFAQ derivatives without TTF moieties. From these results, we speculate that the reduction schemes of 1 and 2 are similar to those of TTPAQ and TTPY‐1‐AQ, as shown in Scheme 2 (for 1 as a representative).…”

“…The reduction process at a low scan rate is worthy of mention (Scheme 2). According to previous reports, [5b,c] the T‐form dication could be reduced to the S‐form neutral state by way of an S‐form cation radical. This was because a positive charge was located on the TTF moiety fused with the TTFAQ moiety to maintain a stable neutral S form of the latter.…”

“…We have developed various TTFAQ analogs and clarified their structures and electrochemical properties [5] . In particular, a bis‐ or tris‐fused donor system composed of one or two TTF(s) and one TTFAQ unit (TTPAQ and TTPY‐1‐AQ in Figure 2a) showed intriguing redox behavior [5b,c] . Taking the example of TTPAQ, two plausible reduction processes from the dication (T form) to the neutral state (S form) and neutral biradical (T form) were observed by cyclic voltammetry, whereas the corresponding oxidation was observed as a simultaneous two‐electron transfer process.…”

“…In addition, as shown in Figure S6 and Table S4, the charge density of neutral 1 and cation radical 1 +. indicate localization of the positive charge on the 1,3‐dithiolium rings and not on the PPh 2 moiety, suggesting that the conformation might change with the positive charge located on the TTFAQ moiety, unlike the case of the TTPAQ and TTPY‐1‐AQ derivatives [5b,c] …”