Abstract
ConspectusA comprehensive understanding of electron transfer (ET) mechanisms in metal nanoclusters (NCs) is pivotal for unlocking their full potential in diverse chemical, biological, and energy-related applications. Owing to their atomic-level structural precision, ET dynamics in metal NCs can be precisely controlled and fine-tuned at the single-molecule or even single-atom level, thereby facilitating the establishment of well-defined structure-ET-application relationships. Furthermore, metal NCs occupy a unique transitional domain between individual atoms and larger nanoparticles, exhibiting distinctive electron-hole Coulombic coupling driven by strong quantum confinement effects. Therefore, investigating ET in metal NCs serves as a critical bridge between traditional molecular ET theories and those developed for larger nanoparticles.In this Account, we summarize our group's recent systematic studies on ET processes in metal NCs. We demonstrate that the ET dynamics of metal NCs are well described by Marcus theory, which predicts a bell-shaped dependence of the ET rate on the driving force. This Marcus-type behavior provides a molecular-level foundation for finely modulating ET rates in metal NC systems. On this basis, we propose three molecular-engineering strategies to regulate ET kinetics in metal NC-molecule assemblies: (i) switching between Rehm-Weller and Marcus ET regimes, (ii) tuning Marcus ET parameters through molecular design, and (iii) implementing proton-coupled ET pathways.The unusual "molecule-like" ET dynamics discovered in metal NCs originate from their discrete energy levels. This allows for direct ET from a single reactant state to a single product state─a process that starkly contrasts with conventional nanoparticles, which display a multitude of product states due to their quasi-continuous energy levels. Such unique ET behavior enables metal NCs to transition from a stepwise ET-proton transfer pathway to a concerted electron-proton transfer process with a significantly reduced energy barrier during proton-coupled ET reactions. Consequently, metal NCs realize both faster and more programmable ET rates, offering enhanced control over ET processes.Leveraging these mechanistic insights, we underscore the significant practical potential of ET kinetics in advancing the fabrication of water-soluble luminophores, biomedical sensing technologies, the oxygen evolution reaction, and the CO reduction reaction. We believe that this Account will not only promote the development of quantitative nanoscale structure-ET-application correlations but also contribute to the refinement of theoretical models for charge transfer chemistry at the nanoscale. Ultimately, these achievements are expected to accelerate the rational design and practical deployment of metal NCs across a wide range of cutting-edge technological fields, including optical probes, biosensing, bioimaging, nanomedicine, catalysis, and advanced optical devices.
