Impact of mechanical bonding on the redox-switching of tetrathiafulvalene in crown ether–ammonium [2]rotaxanes

Abstract

Switchable crown ether–ammonium [2]rotaxanes with a redox-active tetrathiafulvalene (TTF) unit implemented in their wheels were synthesised and fully characterised.

Chiroptical inversion of a planar chiral redox-switchable rotaxane

“…36 Recently, we described redox-switchable rotaxanes, in which the wheels are decorated with tetrathiafulvalenes (TTF). [37][38][39][40][41] TTF can be reversibly oxidised to the TTFc + and TTF 2+ states (Scheme 1). Large-amplitude motion and co-conformational changes in (oligo)rotaxanes were triggered by redox chemistry.…”

Accordion‐Like Motion in Electrochemically Switchable Crown Ether/Ammonium Oligorotaxanes

“…The symmetric oligorotaxanes R n are synthesized by “click” end‐capping (for details, see Supporting Information). Typical chemical shifts, in the 1 H NMR spectra reveal the 24‐crown‐8 ethers in R1 – R3 to encircle the ammonium recognition sites (Supporting Information, Figures S2, S3).…”

“…The non‐ionic rotaxane Ac 1 R1 shows a decrease of E 1/2 1 (−30 mV), but a slightly increased E 1/2 2 value (+30 mV). The increased E 1/2 2 value is assumed to be a result of a diminished accessibility for counterions as it was observed earlier …”

“…The combined experimental results support our proposed switching mechanism for R2 and R3 . Oxidation (TTF→TTF .+ ) leads to charge repulsion between ammonium stations and oxidized wheels, which alone is not sufficient to induce a wheel translation . However, the oxidation also enables non‐covalent TTF–TTF interactions, which additionally counteract the association energy of wheels and axle; hence, the wheel shuttling is a result of an interplay of repulsive and attractive forces.…”

Electrochemically switchable rotaxanes: recent strides in new directions

“…Weak through-space interactions were also found to affect TTF redox-potentials of our recently reported rotaxane shuttles consisting of a TTF-decorated crown ether wheel and a neutral axle. 45 The TTF/TTFc + oxidation was cathodically shied compared to the free TTF-wheel, indicating signicant stabilization of the TTFc + state by interactions between the mechanically bound axle and the TTFc + moiety.…”