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

Switchable crown ether-ammonium [2]rotaxanes with a redox-active tetrathiafulvalene (TTF) unit implemented in their wheels were synthesised and fully characterised. Reversible operation in two modes is possible, in which the [2]rotaxane's axle is either charged or neutral. Cyclic voltammetry experiments reveal the effects of mechanical bonding on the electrochemical properties of TTF and show the [2]rotaxanes to perform a distinct function in both modes. In the charged mode, redox-switching is dominated by strong electrostatic repulsion in the [2]rotaxane which subsequently leads to a macrocycle translation along the axle. In the non-charged mode, a selective energetic stabilisation of TTF radical cations is observed, which can be attributed to an interplay of weak electrostatic interactions between wheel and axle.