Insights into the Excited-State Behavior of Metal Nanoclusters: From Structure-Based Properties to Dynamic Control via Ionic Association

Metal nanoclusters (NCs) possess atomically precise structures and quantized electronic states, exhibiting optical properties derived from electronic transitions between orbitals with discrete energy levels. While the structural behaviors of NCs in the ground state have been extensively studied, their excited-state dynamics remain elusive. The excited-state behavior of NCs may include the relaxation pathways, structural change, and the spatial distribution of excitons. In this account, we first survey how heterometal substitution, surface structure, and environmental factors influence the excited-state relaxation pathways in structurally defined NCs. We then highlight our recent discovery of how the dynamic interaction of counterions with the NC surface has an effect on the properties of the excited state. This ionic interaction in the T1 state leads to changes in its energy, spatial localization, and chiroptical activity. This phenomenon, supported by time-resolved spectroscopy and quantum chemical calculations, represents an emerging strategy for controlling the excited state nature of NCs. By complementing conventional static design approaches, dynamic ion association could provide a powerful tool for designing photofunctional NC materials.