Left or Right? The Direction of Compression-Generated Vortex-Like Flow Selects the Macroscopic Chirality of Interfacial Molecular Assemblies

A new method is described through which the macroscopic chirality of interfacial molecular assemblies of an achiral porphyrin can be mechanically controlled using an original yet efficient Langmuir–Blodgett (LB) technique. By using the unilateral compression geometry, we find that the assemblies deposited from the mirror regions of the LB trough display mirror macroscopic chirality. It is indicated that vortex-like flows could be generated during compression, and that it is the direction of this compression-generated vortex-like flow that determine the macroscopic chirality of the formed assemblies. Moreover, the standard sample-fabrication method with bilateral compression geometry is reformed, and we find that the samples formulated around the left-hand- and right-hand-side Langmuir barriers display opposite macroscopic chiralities. The results suggest that mechanically controlled supramolecular chirogenesis could be efficiently realized through such an LB technique. The investigation establishes a new forum for further investigation of the mechanically induced preferred supramolecular chirality in terms of interfacial organization, and provides the old LB technique with new opportunities for controlling the macroscopic chirality of a supramolecular system that is wholly composed of achiral units.