Tuning the Self-Assembly of Rectangular Amphiphilic Cruciforms

The self-assembly of a series of nonionic amphiphilic cruciforms based on the 1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB) skeleton, in which the peripheral substituents have been modified to modulate the morphology of the supramolecular structures, is reported. The presence of linear paraffinic and hydrophilic chains in TPEBs 1 and 2 gives rise to two-dimensional structures of high aspect ratio. In contrast, the incorporation of dendronized hydrophilic chains results in the formation of twisted ribbons in amphiphile 3 and impedes the organized self-assembly of TPEB 4. Theoretical calculations show that the self-assembly of these amphiphiles might be initiated with the formation of pi-stacked dimeric units. Compound 2, which self-assembles into different morphologies depending on the solvent, interacts by pi-stacking and also by the interdigitation of the peripheral decyl tails to generate bidimensional supramolecular structures. The steric demand exerted by the dendronized polar wedges in 3 and 4 strongly conditions their supramolecular organization. This steric demand together with the interdigitation of the decyl chains results in the self-assembly of cruciform 3 into helical aggregates. However, the lack of the paraffinic chains in 4 impedes this helical organization, and the formation of amorphous material is visualized. The joint experimental and theoretical study presented herein provides relevant guidelines for the modulated self-assembly of nonionic amphiphilic molecules.