Colloidal Assemblies of Chiral Plasmonic Nanoparticles Induce Tunable Circular Dichroism Response

Abstract Plasmonic nanoparticles with strong chiral optical activity are promising systems for a wide range of applications. Self‐assembly of achiral metallic nanoparticles thanks to chiral molecules or templates is a well‐known strategy to prepare chiral plasmonic nanomaterials. In this work, the assembly of chiral plasmonic particles without using a chiral templating agent is investigated. For that purpose, previously developed chiral core‐shell Au@Ag and Au@Au particles are assembled in a controlled way by lowering the surfactant concentration in solution. The assembly leads to pseudo‐linear structures that are revealed by electron microscopy, and the plasmonic responses are characterized by circular dichroism (CD) and UV‐Vis‐NIR spectroscopies. The chiral optical response strongly depends on the system and assembly conditions. For Au@Ag, the CD signal is tuned with contributions appearing in the red region of the spectrum, while for Au@Au, the CD response is unexpectedly lost. The origin of this difference remains undetermined, it is hypothesized that the coupling of circular dichroism modes or the generation of chiral superstructures may influence the chiroptical properties. These experimental results highlight the non‐obvious and complex nature of the chirality generation mechanisms in such plasmonic systems.