Pushing a bistable [2]rotaxane out of equilibrium and isolation of the metastable-state co-conformation.

Incorporating a steric barrier between the two stations in a bistable [2]rotaxane based on monopyrrolotetrathiafulvalene and cyclobis(paraquat--phenylene) allows the high-energy metastable-state co-conformation to be physically isolated following a single redox cycle, thus making it possible to store energy (4.4 J L) and to follow its interconversion back to the ground-state co-conformation.

Insight from Electrochemical Analysis in the Radical Cation State of a Monopyrrolotetrathiafulvalene-Based [2]Rotaxane.

Mechanically interlocked molecules are a class of compounds used for controlling directional movement when barriers can be raised and lowered using external stimuli. Applied voltages can turn on redox states to alter electrostatic barriers but their use for directing motion requires knowledge of their impact on the kinetics. Herein, we make the first measurements on the movement of cyclobis(paraquat-p-phenylene) (CBPQT) across the radical-cation state of monopyrrolotetrathiafulvalene (MPTTF) in a [2]rotaxane using variable scan-rate electrochemistry.

Mechanistic studies of isomeric [2]rotaxanes consisting of two different tetrathiafulvalene units reveal that the movement of cyclobis(paraquat--phenylene) can be controlled.

Controlling the movement in artificial molecular machines is a key challenge that needs to be solved before their full potential can be harnessed. In this study, two isomeric tri-stable [2]rotaxanes 1·4PF and 2·4PF incorporating both a tetrathiafulvalene (TTF) and a monopyrrolotetrathiafulvalene (MPTTF) unit in the dumbbell component have been synthesised to measure the energy barriers when the tetracationic cyclobis(paraquat--phenylene) (CBPQT) ring moves across either a TTF or an MPTTF dication. By strategically exchanging one of the thiomethyl barriers on either the TTF unit or the MPTTF unit with the bulkier thioethyl group, the movement of the CBPQT ring in 1 and 2 can be controlled to take place in only one direction upon tetra-oxidation.

Evaluating the energy landscape of an out-of-equilibrium bistable [2]rotaxane containing monopyrrolotetrathiafulvalene.

The unique redox properties of monopyrrolotetrathiafulvalene can be used to induce directional movement in interlocked molecules. In this study, the kinetics for the directional movement of cyclobis(paraquat--phenylene) across the dioxidised monopyrrolotetrathiafulvalene in a [2]rotaxane is quantified by time-resolved H NMR spectroscopy.

Quantifying the barrier for the movement of cyclobis(paraquat--phenylene) over the dication of monopyrrolotetrathiafulvalene.

A bistable [2]pseudorotaxane 1⊂CBPQT·4PF and a bistable [2]rotaxane 2·4PF have been synthesised to measure the height of an electrostatic barrier produced by double molecular oxidation (0 to +2). Both systems have monopyrrolotetrathiafulvalene (MPTTF) and oxyphenylene (OP) as stations for cyclobis(paraquat--phenylene) (CBPQT). They have a large stopper at one end while the second stopper in 2 is composed of a thioethyl (SEt) group and a thiodiethyleneglycol (TDEG) substituent, whereas in 1⊂CBPQT, the SEt group has been replaced with a less bulky thiomethyl (SMe) group.