Acetal6arenes (Ac6) are introduced as a new class of rigid chiral macrocyclic arenes in which carbon-centered chirality is embedded in a trioxabicyclo3.3.1nonane motif at macrocyclic waist. Ac6 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 Ac6 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 Ac6 display intense circular dichroism (CD) and circularly polarized luminescence (CPL). The associated dissymmetry factors (gabs and glum) even exceed intrinsic Ac6 values, indicating highly efficient chiral transfer. Ac6 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.
Fang et al. (Mon,) studied this question.