Shape-Persistent Anthracene-Based Macrocycles Prepared by Reversible Boronic Ester Formation: Crystallization and Structural Analysis

Abstract

Shape-persistent macrocycles with confined inner spaces have gained significant interest due to their unique properties and potential applications in gas/molecular recognition, nanoscale templates, and nanoelectronics. In this study, we present an efficient synthesis of macrocycles containing anthracene units through reversible boronic ester formation between 1,2-diols and boronic acids. These template-free macrocycles exhibited diverse internal cavities ranging from 11 Å to 20 Å and readily crystallized in solution and on solid substrates. Powder X-ray diffraction analysis revealed that the crystallinity remained after solvent removal. Single crystal X-ray analysis provided detailed insights into the molecular geometry and packing structure. Notably, a macrocycle with phenyl linkers resembles a pseudo-nanocapsule, as the bulky substituents on both sides of the macrocycles prevented the cavity filling by neighbouring molecules. Consequently, the crystalline powders of the macrocycle with phenyl linkers maintained its crystallinity even after annealing, likely resulting in the highest N₂ gas adsorption properties among synthesized macrocycles. This work highlights a robust synthesis strategy for macrocycles, broadening their potential for advanced applications and enabling self-assembled nanoarchitectures.