Extremely strong tubular stacking of aromatic oligoamide macrocycles

Abstract

As the third-generation rigid macrocycles evolved from progenitor <b>1</b>, cyclic aromatic oligoamides <b>3</b>, with a backbone of reduced constraint, exhibit extremely strong stacking with an astoundingly high affinity (estimated lower limit of <i>K</i>_dimer > 10¹³ M^-1 in CHCl₃), which leads to dispersed tubular stacks that undergo further assembly in solution. Computational study reveals a very large binding energy (-49.77 kcal mol^-1) and indicates highly cooperative local dipole interactions that account for the observed strength and directionality for the stacking of <b>3</b>. In the solid-state, X-ray diffraction (XRD) confirms that the aggregation of <b>3</b> results in well-aligned tubular stacks. The persistent tubular assemblies of <b>3</b>, with their non-deformable sub-nm pore, are expected to possess many interesting functions. One such function, transmembrane ion transport, is observed for <b>3</b>.