Supramolecular Gelation of Rigid Triangular Macrocycles through Rings of Multiple C-H•••O Interactions Acting Cooperatively

When equimolar solutions of the enantiomeric naphthalenediimide-based highly rigid triangles R-Delta and S-Delta in ClCH2CH2Cl are mixed, the racemate rac-Delta forms an organogel that is composed of interwoven fibers, resulting from the columnar stacking of the triangles in an alternating R-Delta/S-Delta fashion. Under identical conditions, the pure enantiomers do not form organogels. Density functional theory calculations reveal that the racemic RS dimer is more stable than the RR dimer as a result of the enantiomeric relationship between R-Delta and S-Delta, allowing them to act as two complementary rings comprised of 12 [C-H center dot center dot center dot O] interactions with an unprecedented and uninterrupted circular ADDAADDAADDA.DAADDAADDAAD alignment of hydrogen bond donors (D) and acceptors (A), in contrast with the square wave manner in which the RR dimer forms a complementary yet interrupted ADADAD.DADADA circular sequence of six longer [C-H center dot center dot center dot O] hydrogen bonds. It follows that gelation is favored by weak interactions acting cooperatively in rings under precise stereoelectronic control.