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.Sig-nificant 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 C-H…π in-teractions were responsible for the stabilized self-included conformers.The addition of MeOH or compet-itive 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.