Supramolecular hydrogels and high-aspect-ratio nanofibers through charge-transfer-induced alternate coassembly.

Weak charge-transfer interactions between electron-rich and electron-deficient aromatic molecules have been extensively used for the design of various supramolecular assemblies in solution, such as rotaxanes, catenanes, and foldamers. The conformation of various donor–acceptor (D–A) polymers in solution has been tuned by chargetransfer interactions in synergy with either solvophobic or ion-binding interactions. In addition, extended solid-phase assemblies of alternate donor and acceptor molecules for device applications were attained by cocrystallization and liquid-crystalline mesophase coassembly. Columnar mesophases of alternate donor and acceptor molecules have enhanced columnar organization and higher charge-carrier mobilities compared to their individual components. 1D self-assembled nanowires based on organic p-conjugated systems have attracted a great deal of attention in recent years in the field of organic and supramolecular electronics. 10] Several approaches, which make use of hydrogenbonding and p-stacking interactions, have been used to design self-assembled fibers of donor–acceptor arrays, and create supramolecular p–n heterojunctions for photovoltaics. However, use of charge-transfer interactions for the design of two-component, alternate 1D supramolecular fibers of donor and acceptor molecules in solution is difficult to achieve, as the orthogonal self-assembly (phase separation) of individual components may prevent their efficient coassembly, and hence a careful design of monomers is required. 1D charge-transfer nanofibers are expected to exhibit better conductivity caused by the directional movement of their high-density charge carriers and a well-ordered, stronger p-stacked architecture as a result of better p overlapping of face-to-face-packed aromatic molecules. 13] These observations prompted us to investigate whether nanofibers of alternate donor and acceptor molecules coassembled through charge-transfer interactions can be constructed using supramolecular chemistry design principles. Herein, we show that high-aspect-ratio cylindrical micelles and hydrogels of a donor–acceptor charge-transfer complex can be constructed by self-assembly in water. Although a variety of peptide and rod–coil amphiphiles, as well as sugar derivatives, have been reported to form hydrogels, this is the first report of hydrogel formation that exploits charge-transfer interactions between chromophores. We synthesized a donor–acceptor pair, a coronene tetracarboxylate tetrapotassium salt (CS), and a dodecylfunctionalized methyl viologen derivative (DMV) for the design of coassembled nanostructures (Scheme 1). After