Highly Sensitive, Tunable Chirality Amplification through Space Visualized for Gold Nanorods Capped with Axially Chiral Binaphthyl Derivatives

Abstract

The creation and transmission of chirality in molecular systems is a well-known, widely applied notion. Our understanding of how the chirality of nanomaterials can be controlled, measured, transmitted through space, and applied is less well understood. Dynamic assemblies for chiral sensing or metamaterials engineered from chiral nanomaterials require exact methods to determine transmission and amplification of nanomaterial chirality through space. We report the synthesis of a series of gold nanorods (GNRs) with a constant aspect ratio of ∼4.3 capped with C 2 -symmetric, axially chiral binaphthyl thiols, preparation of dispersions in the nematic liquid crystal 5CB, measurements of the helical pitch, and the determination of the helical twisting power as well as the average distance between the chiral nanomaterial additives. By comparison to the neat organic chiral derivatives, we demonstrate how the amplification of chirality facilitated by GNRs decorated with chiral molecules can be used to clearly distinguish the chiral induction strength of a homologous series of binaphthyl derivatives, differing only in the length of the nontethered aliphatic chain, in the induced chiral nematic liquid crystal phase. Considering systematic errors in sample preparation and optical measurements, these chiral molecules would otherwise be deemed identical with respect to chiral induction. Notably, we find some of the highest ever-reported values of the helical twisting power. We further support our experimentally derived arguments of a more comprehensive understanding of chirality transfer by calculations of a suitable pseudoscalar chirality indicator.

Recent developments in the chiroptical properties of chiral plasmonic gold nanostructures: bioanalytical applications

“…The enhancement of chirality by a related series of polyhedral Au NRs can be employed to identify chirality transfer. The nematic liquid crystal phase reflects the variation in chiral induction strength and facilitated cooperative effects with helically arranged chiral objects [71]. In a polar protic solvent, chiral gold nanoclusters (Au NCs) undergo self-aggregation into supraparticles, while in polar aprotic solvent, self-aggregation does not occur.…”

Chirality Transfer from an Innately Chiral Nanocrystal Core to a Nematic Liquid Crystal: Surface‐Modified Cellulose Nanocrystals

“…The p −1 was then plotted against the CNC weight fraction to give the β w values. [d] The DSF here approaches 1 since the GNRs were capped with a monolayer of Chol‐thiols as determined by TGA and assuming such in the calculations [7b] …”

“… Simplified 3D space filling models demonstrating the difference in the density of surface functionalization between: A) CNCs‐Chol and B) GNR‐Chol based on the calculated number of surface molecules functionalizing only one in eight glucose units on the CNC surface vs. forming a dense cholesterol‐thiol monolayer capping the GNRs [7b] …”

“…% for CNCs‐Chol and 0.02 wt. % for the GNR‐Chol [7b] assuming a constant weight fraction of each cholesterol‐decorated nanorod additive of 0.05 wt. % in the N‐LC), an about eightfold decrease in β w vis‐à‐vis the GNR‐Chol is observed for CNCs‐Chol.…”

Supramolecular Chirality Synchronization in Thin Films of Plasmonic Nanocomposites

“…One route to achieve this goal comprises the incorporation of metal nanoparticles within chiral liquid crystal (LC) matrices. 47 − 50 While yielding materials that exhibit interesting optical properties, this method is limited by the requisite that the organic template must be intrinsically chiral. We propose that achiral constituents can also be used to prepare chiral nanocomposites, which may reduce development costs, if only by broadening the scope of available organic building blocks.…”