From Dynamic Chirality to Stable Enantiomers: Conformational Locking via Synergistic Methylation and Macrocyclization

Restricted by low isomerization barriers, many dynamically chiral molecules often remain racemic, which has hindered their application in chiral functional materials. This work reports a synergistic strategy combining steric methylation with macrocyclization to transform dynamic into static chirality. The macrocycle P5P21 was synthesized by embedding the dynamic unit DPP21 into a pillararene. Structural analyses revealed that the pronounced spatial confinement imposed by the pillararene effectively froze the conformational inversion of DPP21, enabling significant chiroptical activity induced by a single methyl group. This strategy dramatically enhanced emission color purity, narrowing the photoluminescence full width at half maximum (FWHM) from 107 to 41 nm, and boosted the quantum yield (PLQY) from 13.1% to 42.7%, yielding efficient narrowband emission in the near-ultraviolet region (371 nm). Mechanistically, macrocyclic locking not only raised the configurational inversion barrier from 17 kcal/mol to >21 kcal/mol, ensuring conformational stability, but also significantly reduced the excited-state reorganization energy, which is key to narrowband emission. This study provides a versatile design paradigm for stable, efficient chiral luminescent materials.