High Yield Synthesis of Polyrotaxane Constructed from Pillar[5]arene and Viologen Polymer and Stabilization of Its Radical Cation

New polyrotaxane composed of pillar[5]arene and viologen polymer was successfully prepared with extremely high yield by capping the chain ends with adamantyl moieties. Pillar[5]arene and viologen polymer are soluble in various solvents such as acetone, acetonitrile, methanol, DMF, and DMSO, while the polyrotaxane was soluble in DMF and DMSO and insoluble in the other organic solvents. Formation of inter-molecular hydrogen bonds between the OH moieties of pillar[5]arenes stabilized the structure and reduced the solubility. The polyrotaxane exhibited a thermally induced color change from yellow to violet. On heating, the inter-molecular hydrogen bond became weakened, and the shuttling motion of pillar[5]arenes on the polymer axis was fast. Thus, efficient electron transfer from the electron donors of pillar[5]arenes to the electron acceptor of viologen polymer occurred in the whole polymer chain and the radical cation species were stabilized.