Two-Dimensional Supramolecular Polymerization of a Bis-Urea Macrocycle into a Brick-Like Hydrogen-Bonded Network

We report on a dendronized bis-urea macrocycle 1 self-assembling via a cooperative mechanism into two-dimensional (2D) nanosheets formed solely by alternated urea-urea hydrogen bonding interactions. The pure macrocycle self-assembles in bulk into one-dimensional liquid-crystalline columnar phases. In contrast, its self-assembly mode drastically changes in CHCl3 or tetrachloroethane, leading to 2D hydrogen-bonded networks. Theoretical calculations, complemented by previously reported crystalline structures, indicate that the 2D assembly is formed by a brick-like hydrogen bonding pattern between bis-urea macrocycles. This assembly is promoted by the swelling of the trisdodecyloxyphenyl groups upon solvation, which frustrates, due to steric effects, the formation of the thermodynamically more stable columnar macrocycle stacks. This work proposes a new design strategy to access 2D supramolecular polymers by means of a single non-covalent interaction motif, which is of great interest for materials development. A dendronized bis-urea macrocycle forms in bulk columnar liquid-crystalline phases, while in chlorinated solvents it self-assembles into two-dimensional (2D) nanosheets with a brick-like organization. This exotic 2D assembly is enabled by solvent effects and a sophisticated hydrogen-bonding pattern, where each monomer interacts with four vicinal macrocycles only through urea-urea interactions.+image

Automated summary

We reported the self-assembly of a dendronized bis-urea macrocycle into two-dimensional nanosheets via a cooperative mechanism. The self-assembly mode of the macrocycle changed drastically in different solvents, and the formation of two-dimensional networks was promoted by solvent effects and a sophisticated hydrogen-bonding pattern.