Chirality enhancement in macro-chiral liquid crystal nanoparticles

Abstract

The amplification of molecular chirality by metal nanoparticles (NPs) is an important and rapidly evolving field in nanomaterial research with wide applications in smart materials, catalysis, and solvent–solute interactions. Here we present the results of the synthesis of gold nanoparticles (AuNPs) functionalized both with chiral ligands based on the binaphthol motif and with nematogenic groups (ChirAuLC). The materials were characterized chemically and the ratios between chiral groups and LC groups was determined. Synchrotron radiation circular dichroism (SRCD) and synchrotron based X-ray diffraction (XRD) studies show that the AuNPs favoured by the LC state arrange themselves into ordered columns and a helical superstructure appears in the mesophase of collective NPs. A specific focus has been the investigation of the chiral induction of ChirAuLC composites in two different nematic LC hosts. For a number of selected mixtures, the helical twisting power (HTP) of these NPs in systems was calculated from systematic optical observations based on optical polarizing microscopy (OPM). The experimental data show that the HTP of the investigated ChirAuLC composite is significantly larger than that of free “small molecule” chiral groups when dispersed in the same LC host and the chiral transfer efficiency of ChirAuLC is higher than NPs functionalized only with chiral groups (ChirAuNP). This is new and can be explained by a combination of a surface chirality and the domino effect of bound mesogens interacting with the bulk.