An electrochemically switchable foldamer – a surprising feature of a rotaxane with equivalent stations

Abstract

A novel, mechanically interlocked molecular device was obtained from unique supramolecular tectons – π-deficient tetraazamacrocyclic complexes of copper(II) and nickel(II). We present the synthesis of the first rotaxanes based on donor–acceptor interactions involving transition metal complexes. While spontaneous shuttling manifests itself in the variability of the NMR spectra, voltammetric experiments reveal a surprising mode of potential-controlled molecular switching, which does not employ common co-conformational changes. Significantly, it relies on reversible folding/unfolding of the rotaxane. The process is driven by the interplay between electrostatic repulsion and cohesive π–π interaction – a tug of war with a critical point at 1.31 V. Although rotaxanes with equivalent stations are considered degenerate molecular shuttles, we show that this is not the case when an unusual mechanism of switching is involved.