Acetal[6]Arenes: Rigid Chirality‐on‐Annulus Macrocycles Promoting Charge‐Transfer Co‐Assembly With Exceptional (Chiro)Optical Properties

Abstract

ABSTRACT Acetal[6]arenes ( Ac[6] ) are introduced as a new class of rigid chiral macrocyclic arenes in which carbon‐centered chirality is embedded in a trioxabicyclo[3.3.1]nonane motif at macrocyclic waist. Ac[6] efficiently forms charge‐transfer (CT) complexes with electron‐deficient aromatic guests in both solution and the solid state. Single‐crystal x‐ray diffraction reveals that guest molecules bind to the outer surface of Ac[6] through well‐defined stacking interactions. In contrast, the corresponding acyclic bis‐acetal precursors show no complexation behavior, indicating that the rigid macrocyclic topology suppresses ring‐unit flipping and significantly enhances interfacial π–π interactions. The resulting solid‐state complexes exhibit dual emission at CT band (prompt fluorescence and TADF). Notably, complexes derived from enantiopure Ac[6] display intense circular dichroism (CD) and circularly polarized luminescence (CPL). The associated dissymmetry factors ( g abs and g lum ) even exceed intrinsic Ac[6] values, indicating highly efficient chiral transfer. Ac[6] shows robust guest‐capture capability, forming CT complexes not only via solution co‐crystallization but also through simple physical mixing and even gas‐phase guest uptake. By exploiting time‐dependent capture kinetics and multicolor optoelectronic properties, we developed applications for optical sensing and time‐encoded encryption. These results establish macrocyclization of rigid chirality‐on‐annulus units as a powerful strategy for creating functional supramolecular CT materials with emergent chiroptical and optoelectronic properties.