Tunable Plasmonic Circular Dichroism of Hierarchical Chiral Assemblies

Plasmonic circular dichroism (PCD) is a powerful approach for enhancing chiroptical effects at the nanoscale with promising applications such as optical information processing, sensing, and catalysis. However, a key challenge remains in achieving both strong and tunable optical responses. While most strategies use either intrinsically chiral nanoparticles (NPs) or achiral NPs arranged into chiral assemblies, combining both offers a promising route to amplify chiral optical responses. Here, 4-fold-twisted gold nanorods (cGNRs) were assembled by depletion-induced self-assembly (DISA) into chiral superstructures with tunable PCD properties. By reducing cGNR helicity via chemical etching, we study how building block helicity affects hierarchical structure formation. Whereas static helical supercrystals were obtained on substrates upon evaporation-induced self-assembly (EISA), DISA allowed us to dynamically modulate the interparticle distance in solution from 13 ± 1.2 nm to 6.9 ± 1.0 nm. The assembly/disassembly process was found to be fully reversible, thereby enabling a modulation of the g-factor by 2 orders of magnitude with a switching rate of approximately 1 h. Beyond achieving high dissymmetry factors of 0.2, our approach establishes a reconfigurable PCD platform that is free from ligand exchange constraints and compatible with different NP shapes. Though response times remain too slow for optical computing, these findings are relevant for the development of optical modulators and memory devices based on dynamic chiral metafluids.