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

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.