Discrete Stacking of Aromatic Oligoamide Macrocycles

Unlike the precise structural control
typical of closed assemblies,
curbing the stacking of disc- and ring-shaped molecules is quite challenging.
Here we report the discrete stacking of rigid aromatic oligoamide
macrocycles 1. With increasing concentration, the aggregation
of 1 quickly plateaus, forming a discrete oligomer, as
suggested by 1D 1H, 2D nuclear Overhauser effect, and diffusion-ordered
NMR spectroscopy. Quantum-chemical calculations indicate that the
tetramer of 1 is the most stable among oligomeric stacks.
X-ray crystallography revealed a tetrameric stack containing identical
molecules adopting two different conformations. With a defined length
and an inner pore capable of accommodating distinctly different guests,
the tetramers of 1 densely pack into 2D layers. Besides
being a rare system of conformation-regulated supramolecular oligomerization,
the discrete stacks of 1, along with their higher-order
assemblies, may offer new nanotechnological applications.

与封闭组装体典型的精准结构调控不同，抑制盘状与环状分子的堆叠颇具挑战性。本文报道了刚性芳香寡酰胺大环化合物1的离散堆叠行为。随着浓度升高，化合物1的聚集过程快速进入平台期，最终形成离散寡聚体，该结论得到一维氢谱（1D ¹H NMR）、二维核Overhauser效应谱（2D nuclear Overhauser effect spectroscopy）以及扩散排序核磁共振谱（diffusion-ordered NMR spectroscopy）的佐证。量子化学计算结果表明，在1的寡聚堆叠体中，四聚体是最稳定的组装形式。X射线晶体衍射分析显示，该四聚堆叠体由相同分子构成，但呈现两种不同的构象。该四聚体具有确定的长度，且内部孔道可容纳结构差异显著的客体分子，因此能够紧密堆积形成二维层状结构。作为一种罕见的构象调控型超分子寡聚化体系，化合物1的离散堆叠体及其高阶组装体有望为纳米技术领域带来全新应用场景。