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

Abstract

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.

Interfacial organization of achiral porphyrins via unidirectional compression: a general method for chiroptical porphyrin assemblies of selected chirality

“…80%) samples display negative CD signals. These statistical results show a similar tendency to those of the samples constructed by using a compression speed of 0.2 mm per second, 25 preliminarily suggesting that the compression direction and/or the deposition region might be the main factor that determines the macroscopic chirality of the interfacial assemblies, while the compression speed might contribute less to this issue.…”

“…25 As shown in Fig. 1A (top panel), for typical samples assembled by compression from the left-hand side, the assemblies formed at the front side of the Langmuir trough exhibit a negative CD signal around 438 nm, while those formed at the back side of the trough display a mirror-imaged CD curve.…”

“…25 It was found that the chirality of the assemblies was determined by the direction of the compression-generated vortex-like flow. However, it still remains an open yet significant question whether such an interfacial protocol is similar to the directional stirring and spin-coating based strategies such that it could only be limited to specific porphyrins (TPPMe), or it, to some extent, is a general method to control the chirality of the assemblies of a wide variety of achiral porphyrins.…”

Stirring competes with chemical induction in chiral selection of soft matter aggregates

“…More striking is the report that the combination of soft aggregation and stirring may lead not only to chiral induction 22,23 but, more importantly, also to sign selection, in both three 24,25 and two dimensions 26,27 . Discussions on the true nature of such an enantioselection in three-dimensional aggregates have raised some controversy [28][29][30][31][32][33] .…”

Assembly of π‐Conjugated Nanosystems for Electronic Sensing Devices

“…[26] Consequently, patterned nanoarrays, nanostripes, nanofibers, nanoparticles, nanotubes, and even chiral assemblies could be fabricated. [24,[27][28][29][30] For example, Chen et al reported that by taking the advantage of their thinner and flexible gold nanowires (AuNWs) building blocks, giant superlattice nanomembranes could be fabricated via LB techniques. [31,32] It was found that high transparency, conductivity, and stretchability could be achieved simultaneously in such single-layer AuNWs superlattice nanomembrane, which make them facile to be integrated into lightweight, foldable optoelectronic devices with low consumption of materials and energy.…”