Hierarchical Self-Assembly of a Porphyrin into Chiral Macroscopic Flowers with Superhydrophobic and Enantioselective Property

Supramolecular self-assembly provides an efficient way to fabricate simple units into various hierarchical nano/microstructures, which could mimic the bioself-assembly and develop functional materials. Since chiral molecules and chiral nanostructures are widely adopted by biological systems, an introduction of the chiral factor into the self-assembly process will provide better understanding of the biological systems. Here, using a chiral amphiphilic histidine to assist the self-assembly of a porphyrin with four carboxylic acids, we obtained hierarchical chiral nano- to microstructures. We have found that through the hydrogen bonds/electrostatic interactions between the porphyrin and histidine derivatives, the pi-pi stacking between the porphyrins, and hydrophobic interactions between the amphiphilic histidine, the two components could self-assemble into chiral nanohelices and microflowers. The supramolecular chirality of these structures was confirmed by scanning electron microscopy images as well as the circular dichroism spectra, which was found to follow the molecular chirality of the histidine derivative. More interestingly, the microflower structures formed a superhydrophobic and chiral surface, which exhibited macroscopic enantioselective recognition of some and D-amino acids via contact angle measurements.