Coupling Dichroism in Strong-Coupled Chiral Molecule-Plasmon Nanoparticle System

The interaction between intense light-matter not only promotes emerging applications in quantum and nonlinear optics but also facilitates changes in material properties. Plasmons can significantly enhance not only molecular chirality but also the coupling strength. In this study, we investigate the coupling dichroism in a strongly coupled chiral molecule–plasmon nanoparticle system using real-time propagation time-dependent density functional theory (RT-TDDFT). By simulating the interaction between L/D-Phenylglycinol molecules and chiral aluminum clusters (Na-doped Al197Na4), we examine the effects of molecular chirality, cluster chirality, and the coupled effect in the system. Our results demonstrate that the achiral/chiral clusters induce significant spectral shifts and enhance molecular circular dichroism (CD) signals due to strong plasmon-molecule coupling. The electric-field distribution and transition contribution maps (TCMs) reveal the formation of bonding and antibonding polaritonic modes, modulated by molecular proximity to the cluster. Both of the coupling factor and decay rate of the coupled system will be modulated by the chirality of the molecules and the cluster. Furthermore, we find that increasing the number of coupled molecules leads to a substantial increase in the intensity of lower polaritonic modes, highlighting the collective behavior in multimolecule systems due to the modal crosstalk or resonance between cluster chirality and molecular chirality. These findings provide valuable insights into the fundamental mechanisms governing plasmonic-enhanced chirality at the atomic scale, which have implications for the design of highly sensitive chiral sensors and optoelectronic devices.