A Covalent Organic Helical Cage with Remarkable Chiroptical Amplification

Purely organic shape-persistent chiral cages are designed through the use of rigid chiral axes. Covalent dimerization of a tripodal fragment bearing chiral allenes forms a molecular twisted prism with loop-like lateral edges presenting 10-fold chiroptical amplification compared to its isolated building blocks. The expected geometry of covalent organic helical cage (M,M)3 -1 was confirmed by X-ray crystal structure analysis. Comparison of the chiroptical responses of this shape-persistent molecular container with more flexible analogues highlights how the control of the conformational freedom of the molecule can be used to obtain molecular cages with strong chiroptical responses. Selective inclusion-complex formation with ferrocenium ions [(P,P)3 -1@Fc(+) ] was confirmed and quantified with HR-ESI-MS and NMR spectroscopy.