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

Abstract

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.

Synthesis of novel pillar-shaped cavitands “Pillar[5]arenes” and their application for supramolecular materials

“…The reaction mixture was evaporated to dryness and the residue was washed several times with acetonitrile to give the polyrotaxane. The pillar [5]arene-based polyrotaxane was isolated in an extremely high yield (93%), due to the high stability of the complexes between 6 and the viologen polymer [103]. Such stability in organic media is quite different from that of CD-based polypseudorotaxanes [104].…”

Radical-radical rotaxanes with tetracationic cyclophane ring, and quaternary azaaromatic rotaxanes with cage macrocycles

“…In this way the formation of polyrotaxane 16 leads to stabilization of viologen radical cations. 61 In 16 an intermolecular hydrogen bond between pillararenes exists, and slow shuttling occurs. Upon heating this hydrogen bond is weakened, and the shuttling of pillarenes occurs freely and becomes faster.…”

Polyrotaxanes

“…These examples include various macrocycles, for example, crown ethers (CEs) (6)(7)(8)(9), cyclophanes (CPs) (10,11), calix[n]arenes (12)(13)(14), CDs (15)(16)(17)(18)(19), cucurbiturils (CBs) (20), cyclobis(paraquat-p-phenylene) (21), and pillararenes (22)(23)(24), and numerous types of axes depending on the macrocycles. As shown in Figure 1, polyrotaxanes are categorized into two classes based on their structure: main-chain polyrotaxanes and side-chain polyrotaxanes.…”