Close Packing in Trans Conformers Promotes the Formation of Supramolecular Structures with C Symmetry.

Assemblies with C symmetry exhibit important applications in many fields such as enantioselective catalysis. However, their formation is challenging due to their large entropic disadvantage, and molecular information on their formation dynamics is limited because of the lack of effective characterization techniques. Here, using achiral amphiphilic molecules such as N-oleoyl ethanolamide (OEA) and its analogues as modeling assembly units, we demonstrated that the sss polarization signals, generated by femtosecond sum frequency generation vibrational spectroscopy (SFG-VS), provide a powerful tool to monitor the formation dynamics of the C symmetric supramolecular structures at the interfaces. The trans conformation of the assembly units can provide strong π-π interactions and thus produce enough enthalpy to drive the formation of C symmetric supramolecular structures. However, the cis conformation impedes the assembly of C symmetric structures and cannot generate sss and chiral polarization SFG signals. These findings may aid in rationally constructing ordered and functional superstructures and understanding the mechanism of chirality formation.