Chiral Plasmonic Excitation-Controlled Galvanic Replacement Reaction

High Resolution Image Download MS PowerPoint Slide The induction of chirality in the shape of metal nanoparticles using circularly polarized light (CPL) offers a ligand-free pathway to chiral plasmonic materials, yet the mechanism(s) underlying this symmetry breaking in colloidal systems is largely unknown. Here, we present a comprehensive mechanistic study of CPL-controlled galvanic replacement reactions (GRR) in freely rotating colloidal core–shell Au@Ag nanobars (AgNBs), using Au 3+, Pt 4+, and Pd 4+ halide complexes. We demonstrate that plasmon excitation significantly accelerates the GRR and promotes regioselective silver oxidation and redeposition, leading to significant circular dichroism (CD) signals at plasmon resonance peaks. It was found that CPL induces chirality via a two-step reaction: The first several seconds of CPL-controlled GRR contribute about half of the CD signal magnitude. Slower (several minutes) plasmon-induced silver redeposition contributes to the other half of the CD signal and is affected by the presence of halide ions and by the symmetry breaking in the first part. Optimal CD peak intensities were achieved in cases where the light-induced GRR was significantly faster than the dark GRR. Halide identity and the pH level strongly affected both the GRR rates and optical activity.