Pillar-like Macrocycle Reversibly Self-Assembled from a Molecular Thermally Activated Delayed Fluorescence Emitter Based on B ← N Dative Bonds with Intriguing Fluorescence

Incorporating boron atoms into organic macrocycles imparts unique chemical, electronic, and optical properties. The concept of making use of dative boron-nitrogen (B ← N) bonds for the construction of macrocycles has been proposed, but very few examples have been prepared with functional structures, much less pillar-like and other prismatic macrocycles, and their various functionalities have not been fully exploited. Here, we introduce a "functional molecular wall" synthetic protocol based on the self-assembly characteristics of B ← N dative bonds to construct highly symmetrical macrocycles, forming a quasi-pentagonal-shaped macrocycle (named [5]pyBN-p) with a pillar-like structure. Single-crystal analysis confirmed that its structure exhibited a 5-fold symmetric crown-shaped cavity with a diameter of approximately 9.65 Å, forming four sets of three-dimensional channel stacking structures. In solution, thermal cycling between heating and cooling allows for a fast and fully reversible conversion between monomer pyBN-p and pentameric macrocycle [5]pyBN-p. The resultant macrocycle [5]pyBN-p exhibited delayed fluorescence (DF) property and high photoluminescence quantum yield in the solid state. Notably, the supramolecular aggregates of macrocycle [5]pyBN-p possessed permanent porosity and showed an efficient C₂H₆/C₂H₄ inverse separation capacity. This work highlights a new molecular design strategy for B ← N-containing macrocycles, enriching the family of molecular species and expanding new avenues for their applications.