Symmetry-breaking host-guest assembly in a hydrogen-bonded supramolecular system

Bio-inspired self-assembly is invaluable to create well-defined giant structures from small molecular units. Owing to a large entropy loss in the self-assembly process, highly symmetric structures are typically obtained as thermodynamic products while formation of low symmetric assemblies is still challenging. In this study, we report the symmetry-breaking self-assembly of a defined C₁-symmetric supramolecular structure from an O_h-symmetric hydrogen-bonded resorcin[4]arene capsule and C₂-symmetric cationic bis-cyclometalated Ir complexes, carrying sterically demanding tertiary butyl (^tBu) groups, on the basis of synergistic effects of weak binding forces. The flexible capsule framework shows a large structural change upon guest binding to form a distorted resorcin[4]arene hexameric capsule, providing an asymmetric cavity. Location of the chiral guest inside the anisotropic environment leads to modulation of its Electric Dipole (ED) and Magnetic Dipole (MD) transition moments in the excited state, causing an increased emission quantum yield, longer emission lifetime, and enhancement of the dissymmetry factor (g_lum) in the circularly polarized luminescence.