Mutual complexation between p-p stacked molecular tweezers

Aromatic and heterocyclic molecules which form electronically complementary p-p stacked complexes have recently found extensive application in functional materials, molecular machines, and stimuli-responsive supra- molecular polymers. Here we describe the design and synthesis of model compounds that self-assemble through complemen- tary 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 p-electron rich dipyrenyl tweezer-motif and a tweezer-like, p-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 p-stacks, and supporting hydrogen bonds between pyrenyl amide NH groups and diimide carbonyl oxygens were identified.