Mutual Complexation between π–π Stacked Molecular Tweezers

Aromatic and heterocyclic molecules which form electronically complementary π–π stacked complexes have recently found extensive application in functional materials, molecular machines, and stimuli-responsive supramolecular polymers. Here we describe the design and synthesis of model compounds that self-assemble through complementary stacking motifs, paralleling those postulated to exist in high-molecular weight, healable, supramolecular polymer systems. Complexation studies using 1H NMR and UV–vis spectroscopy indicated formation of a complementary complex between a π-electron rich dipyrenyl tweezer-motif and a tweezer-like, π-electron deficient bis-diimide. The binding stoichiometry in solution between the chain-folding diimide and the pyrenyl derivative was equimolar with respect to the two binding motifs, and the resulting association constant was measured at Ka = 1200 ± 90 M–1. Single crystal X-ray analysis of this “tweezer–tweezer” complex showed a low-energy conformation of the triethylenedioxy linker within the bis-diimide chain-fold. Interplanar separations of 3.4–3.5 Å were found within the π-stacks, and supporting hydrogen bonds between pyrenyl amide NH groups and diimide carbonyl oxygens were identified.