Domino‐Redox Reaction Induced by An Electrochemically Triggered Conformational Change

Abstract

The concept of a domino‐type reaction has been applied in a wide range of fields such as synthetic organic chemistry, material engineering, and life science. To extend the domino concept to redox chemistry, we designed and synthesized a dimeric quinodimethane (QD) with a nonplanar dithiin spacer. The domino‐redox properties can be activated by raising the temperature, based on a thermally equilibrated twisted conformation of QD, which has a higher highest occupied molecular orbital (HOMO) level that is more readily oxidized. After one QD unit is oxidized (trigger), steric repulsion and electronic interaction between electrophores make the neighboring QD unit adopt a twisted conformation (domino process), which facilitates the following oxidation. Thus, a domino‐redox reaction was achieved for the first time by a change in the HOMO level due to a drastic change in the molecular conformation.

Redox-Switchable Aromaticity in a Helically Extended Indeno[2,1-c]fluorene

“…As shown in Figure a, only one redox wave is observed in both anodic and cathodic scan directions with peak potentials of E pa = +0.37 and E pc = +0.08 V vs Fc/Fc + , respectively (at a scan rate of 100 mV/s). This corresponds to a moderate but notable hysteresis of 290 mV, which is in good agreement with the dynamic nature of the switching process, whereby simultaneous two-electron redox is associated with significant geometric rearrangements from a folded to a twisted state. , This behavior is also observed in a range of related redox-active overcrowded alkenes, ,,, including the parent BTX , which, due to its more significant crowding in the fjord region, displays an even larger hysteresis (∼800 mV). , …”

“…This corresponds to a moderate but notable hysteresis of 290 mV, which is in good agreement with the dynamic nature of the switching process, whereby simultaneous two-electron redox is associated with significant geometric rearrangements from a folded to a twisted state. 41,45 This behavior is also observed in a range of related redox-active overcrowded alkenes, 43,48,63,64 including the parent BTX, which, due to its more significant crowding in the fjord region, displays an even larger hysteresis (∼800 mV). 41,45 The hysteretic nature of this process is also apparent in the first CV scan shown in Figure 7a.…”

“…The removal of an electron from this radical cation is at least as facile, or even more facile, than the initial oxidation and thus occurs immediately, thereby generating rac - 1 2+ (potential compression/inversion, Figure S23). However, alternative mechanisms in which a conformational rearrangement precedes electron transfer , cannot be ruled out, as discussed in detail in the Supporting Information (Figures S24–S26). Regardless of the exact mechanism, oxidation (as well as reduction) proceeds without the buildup of the potentially reactive radical cation intermediate, an important feature of this system that undoubtedly contributes to its high degree of reversibility and stability (vide infra).…”

“…This problem is circumvented in dynamic redox (dyrex) switches, wherein two-electron redox processes are associated with significant geometric rearrangements. − This has been exploited in dyrex switches, in which reversible C–C single or CC double-bond formation/breaking via two-electron oxidations gives rise to not only significant conformational transformations but also changes in polarity, absorbance, and luminescence. − For example, we have pioneered the use of the overcrowded alkene bisthioxanthylidene ( BTX , Figure ) ,− and derivatives thereof as highly versatile redox and photoresponsive switches with multiple stable and isolable (redox) states.…”