Introducing Prism[4]arene: A Macrocycle with Enantiomerically Resolvable Inherent Chirality and Intriguing Chiroptical Properties

This study presents the first report of an inherently chiral prismarene with resolved enantiomers. Prism[4]arenes, synthesized via a thermodynamic template approach using a tailor-made selective cation, effectively maintain their chirality due to their strained macrorings and narrow annuli, which prevent the flipping of naphthalene rings. The solid-state structure of the synthesized PrS[4]iPe revealed a racemic crystal composed of all-pR and all-pS enantiomeric pairs, forming supramolecular polymeric chains of homochiral molecules interlinked by intermolecular host-guest interactions. Both enantiomers were resolved by using chiral high-performance liquid chromatography (HPLC), and their chiroptical properties were thoroughly investigated. Configurational assignment was achieved through time-dependent density functional theory (TDDFT) computations alongside electronic circular dichroism/ultraviolet-visible (ECD/UV-vis) spectral analysis. Notably, the circularly polarized luminescence (CPL) properties exhibited a significant dissymmetry ratio of 0.008 for these prism[4]arenes, due to electric and magnetic dipole transition moments both directed along the cylinder axis. Furthermore, the ability of PrS[4]iPe to achieve enantioselective recognition with chiral ammonium guests was demonstrated.