Molecular Compasses for Modulating Electronic Communication in Pillar[5]quinone

Abstract

Just as a pointer, which moves freely and points to the magnetic North in a compass, affords us with a device for tracking direction on a global scale, a dipole moment in a molecule is capable of aligning itself in a compass-like manner in response to an electric field at the molecular level. Here, we demonstrate that dipole moment pointers, based on amide and ester groups in the dumbbell components of [2]rotaxanes, are susceptible to changes in pole–dipole and dipole–dipole interactions within a redox-active pillar[5]quinone ring component when subjected to redox control. Distinct from free pillar[5]quinone, these molecular compasses exhibit a 1–1–1–1–1 electron-uptake pattern during the first-electron transfers. Density functional theory (DFT) calculations reveal that, upon the reduction of quinoid units in the amide-based molecular compass, the positive end of the dipole moment pointer in the dumbbell component becomes oriented toward the reduced anionic quinone in the ring component, courtesy of hydrogen bonding. The negative end of the dipole moment pointer in the dumbbell component lowers the reduction potentials of the other four quinoid units as a result of electrostatic repulsions, which explain its 1–1–1–1–1 electron-uptake pattern. Our findings highlight how electronic communication between the dipole moment pointers and the quinoid units in the ring component enables the [2]rotaxane to act as a molecular compass, precisely reorienting its dipole moments in response to redox changes.