Solid-State Characterization and Photoinduced Intramolecular Electron Transfer in a Nanoconfined Octacationic Homo[2]Catenane

An octacationic homo[2]­catenane comprised of two mechanically interlocked cyclobis­(paraquat-p-phenylene) rings has been obtained from the oxidation of the septacationic monoradical with nitrosonium hexafluoroantimonate. The nanoconfinement of normally repulsive bipyridinium units results in the enforced π-overlap of eight positively charged pyridinium rings in a volume of <1.25 nm3. In the solid state, the torsional angles around the C–C bonds between the four pairs of pyridinium rings range between 16 and 30°, while the π–π stacking distances between the bipyridinium units are extended for the inside pair and contracted for the pairs on the outsidea consequence of Coulombic repulsion between the inner bipyridinium subunits. In solution, irradiation of the [2]­catenane at 275 nm results in electron transfer from one of the paraphenylene rings to the inner bipyridinium dimer, leading to the generation of a temporary mixed-valence state within the rigid and robust homo[2]­catenane.