Chiroptical switching of molecular universal joint triggered by complexation/release of a cation: A stepwise synergistic complexation

Pillar[5]arene-based molecular universal joints (MUJs), bearing fused crown ether subring (MUJ1 and MUJ3) or a ring without ether oxygen atom (MUJ2), were synthesized and enantio‑differentiated. Significant chiral inversion was observed for the crown ether-fused MUJs upon the addition of equivalent cations Na+, showing an anisotropy (g) factor of 0.014, while alkyl subring-fused MUJ2 showed no CD inversions. Unprecedentedly, sodium ion triggered rolling-in motion of the subring to the pillar[5]arene cavity was verified, and the synergistic noncovalent interaction of cation-π interactions and CH…π interactions were responsible for the stabilized self-included conformers. The addition of MeOH or competitive hosts 15-crown-5 ether disassembled the complex of MUJ1 and Na+ followed by a rolling-out of the subring, which made the sodium-ion triggered chiroptical switching reversible.