Chirality transfer in nematic liquid crystals doped with (S)-naproxen-functionalized gold nanoclusters: an induced circular dichroism study

In a recent study, we found that nematic liquid crystals ( N-LCs) doped with chiral (S)-naproxen-functionalized dodecane thiolate protected gold nanoclusters ( Au2, Au3) or non- chiral alkyl thiolate protected Au clusters ( Au1) produce thin film textures with characteristic uniform stripe patterns separated by areas of homeotropic alignment. While these textures closely resemble textures commonly observed for chiral nematic ( N*-) phases with large helical pitch, so- called cholesteric finger textures, they originate from local concentration differences of the nanoclusters in the N- LC solvent. While areas with higher particle content form linear particle aggregates ( stripe domains) due to the surface anchoring of the N- LC molecules to the cluster surface, areas of lower particle concentration give homeotropic alignment as a result of particles residing at the glass-N-LC interfaces. To elucidate and confirm a chirality transfer from the chirally modified gold clusters to the non- chiral N- LC, despite the complex thin film textures, we here present detailed induced circular dichroism ( ICD) studies of thin films of 5CB doped with the three different Au clusters. These experiments revealed that the chiral Au nanoclusters ( Au2, Au3) successfully transfer chirality to the N- LC host producing a chiral nematic phase ( N*) with the opposite helical sense in comparison to the pure, organic chiral dopant dispersed in the same N- LC host. Thus, these results provide the first experimental proof for the usefulness of gold nanoclusters as chiral dopants for N- LCs. In contrast, for the non- chiral Au cluster, at a macroscopic level, no relationship between the cholesteric finger-like textures and chirality was found.