Flow Effects in Supramolecular Chirality

Abstract

There are an increasing number of reports on the emergence of circular dichroic signals when solutions of J‐aggregates are vortex‐stirred. Some authors claim that the transfer of chirality from the macroscopic stirring vortex occurs at the level of electronic transitions. Others argue that the signal observed is not due to true circular dichroism (CD), but rather that it is an artifact due to combinations of linear polarization contributions. For both interpretations it is necessary to assume that the alignment by effect of flows dominates over the Brownian dynamics. Therefore, the topic belongs to supramolecular chemistry because the alignment in current flows can only occur for relatively large particles with an appropriate shape. The phenomenon is detected by CD spectroscopy, which itself is also the main hindrance, even controversial, in its study and interpretation. However, modern Mueller matrix polarimetry can solve some of the problems. The phenomenon has been explained using different scenarios; however, in some of the systems the experimental evidence only supports the model in which deformation (folding/torsion) of elastic soft‐matter yields true CD. Here we discuss the role of the gradient of shear rates in the deformation of nano particles of soft matter to give chiral supramolecular structures, as the first step to explaining the phenomenon.

Kinetic Control of the Supramolecular Chirality of Porphyrin J‐Aggregates

“…Notice that this chiral effect is not related to the emergence of chirality by vortex stirring previously reported for elongated J-aggregate particles of H 4 TPPS 3 (irreversible effect) [9] or H 4 TPPS 4 (reversible effect), [7,8] which have been attributed to the mechanical deformation of the initially straight particles into chiral folded structures (see refs. [9][10][11]).…”

Hydrodynamic Effects in Soft‐matter Self‐assembly: The Case of J‐Aggregates of Amphiphilic Porphyrins

“…Furthermore, mechanical effects may lead to plastic changes in the nanoparticle structure, for example transforming hollow monolayered nanotubes into bilayered ribbons. Despite the lack of enough experimental proofs, elastic changes may occur for some type of particles, e. g. nanotubes under the action of the shear force of laminar flows …”

Hydrodynamic and Thermophoretic Effects on the Supramolecular Chirality of Pyrene‐Derived Nanosheets

“…Both detection and induction of such chiroptical properties in the intentional absence of a chemical bias have been studied intensely over the past years 16. 20 However, very few researchers paid sufficient attention to the preparation methodology and correlation of the chiroptical response with final morphology of self‐assemblies 21. Recently, it has been shown that the pathway complexity of aggregation of the classic meso ‐tetra(4‐sulfophenyl) (TPPS) porphyrin influences the final chiroptical response 22…”