Pressure-driven, solvation-directed planar chirality switching of cyclophano-pillar[5]arenes (molecular universal joints)

Abstract

Planar chiral cyclophanopillar[5]arenes with a fused oligo(oxyethylene) or polymethylene subring (<b>MUJ</b>s), existing as an equilibrium mixture of subring-included (in) and -excluded (out) conformers, respond to hydrostatic pressure to exhibit dynamic chiroptical property changes, leading to an unprecedented pressure-driven chirality inversion and the largest ever-reported leap of anisotropy (<i>g</i>) factor for the <b>MUJ</b> with a dodecamethylene subring. The pressure susceptivity of <b>MUJ</b>s, assessed by the change in <i>g</i> per unit pressure, is a critical function of the size and nature of the subring incorporated and the solvent employed. Mechanistic elucidations reveal that the in-out equilibrium, as the origin of the <b>MUJ</b>'s chiroptical property changes, is on a delicate balance of the competitive inclusion of subrings <i>versus</i> solvent molecules as well as the solvation of the excluded subring. The present results further encourage our use of pressure as a unique tool for dynamically manipulating various supramolecular devices/machines.