Uncovering the Origin of Chirality from Plasmonic Nanoparticle/Cellulose Nanocrystal Composite Films

Abstract Chirality generated by the co‐assembly of plasmonic nanoparticles (NPs) and chiral photonic crystals has attracted broad interest owing to its strong optical activities. However, it is difficult to understand the physical mechanism of the unique chiral responses, for surface‐plasmon‐mediated circular dichroism (SP‐CD) is a hybrid response generated from chiral plasmonic–photonic systems. This study aims to investigate how chirality is generated by this system and the relationship between SP‐CD and plasmonic–photonic couplings. Here, quasi‐continuous plasmon bands are designed to interact with the different photonic bandgaps of cellulose nanocrystals (CNCs). In spectroscopy and simulation, characteristic SP‐CD shape lines derived from the extinction dispersion of plasmonic NPs for circularly polarized light in the CNCs are observed. It is demonstrated that this plasmonic chirality is determined by the coupling states and originates from a multiple scattering combination of plasmonic NPs under a chiral excitation field. A novel transfer‐matrix method is established to perform numerical analysis of this complex multiple scattering efficiently. This study is expected to offer a deep insight into chiral plasmonic–photonic systems.