Pressure effects in the synthesis of isomeric rotaxanes.

Pressure not only influences the yield in the synthesis of a two-station [2]rotaxane, it also determines the distribution of the co-conformational isomers. At high pressure cyclobis(paraquat-p-phenylene) is preferentially assembled around a monopyrrolotetrathiafulvalene unit, while at low pressure it is preferentially assembled around a hydroquinone unit.