Locking down the electronic structure of (monopyrrolo)tetrathiafulvalene in [2]rotaxanes.

[reaction: see text] The redox potentials of a highly constrained [2]rotaxane have been measured and used to model the energy of the HOMO of tetrathiafulvalene-based bistable [2]rotaxanes in their two co-conformationally isomeric states. Restrained from co-conformational movements, the measured oxidation and reduction potentials provide insights into the orbital energies and electronic structure of a (monopyrrolo)tetrathiafulvalene unit when encircled by a tetracationic cyclobis(paraquat-p-phenylene) ring.