Atomically Precise Metal Nanoclusters for Near-Infrared-II Photonics.

ConspectusLight in the near-infrared-II (NIR-II, 1000-2500 nm) region has enabled groundbreaking advances in photonic technologies, including long-distance optical communication, deep-tissue optical imaging, noninvasive neuromodulation, and high-efficiency solar energy conversion. Traditional NIR-II-responsive materials, such as rare-earth nanoparticles, carbon nanotubes, quantum dots, and organic chromophores, have achieved important progress. However, their performance is often constrained by intrinsic drawbacks, including narrow spectral response, low quantum yields, toxicity, and/or poor stability.Recently, atomically precise metal nanoclusters (NCs), which bridge the gap between small molecules (e.g., complexes) and plasmonic nanoparticles, have emerged as a transformative platform for NIR-II photonics. Their tailorable compositions and atomic-level geometric structures give rise to versatile electronic structures, enabling highly controllable NIR-II absorption and emission and precise structure-property correlations. To date, metal NCs have demonstrated superior sensitivity in NIR-II light absorption, broad spectral responsiveness, and high photon-generation efficiency, outperforming many conventional NIR-II materials. These attributes make metal NCs particularly attractive for applications requiring high optical performance, spectral tunability, and biocompatibility.In this Account, we summarize recent progress in the design, synthesis, and functionalization of NIR-II-responsive metal NCs. We highlight three major design principles that have driven advances in this field: (1) structural anisotropy, which promotes electron delocalization and enhances radiative transitions; (2) heteroatom doping, which modifies electronic transition dipoles and exciton relaxation pathways; (3) ligand engineering, which modulates energy dissipation within NCs and between NCs and their surrounding environment. Together, these approaches offer a versatile framework for controlling NIR-II photon absorption, conversion, and emission at the atomic scale.Additionally, we discuss emerging applications of NIR-II-active metal NCs in deep-tissue optical bioimaging, photothermal therapy, and photocatalysis. The integration of precise structural control with tunable NIR-II optical properties opens new frontiers for next-generation photonic systems, where light manipulation at the atomic level can translate into transformative advances in biomedicine, sensing, and renewable energy technologies. Looking forward, continued exploration of novel NC structures, dopant chemistry, and surface functionalization will further expand the potential of metal NCs in NIR-II photonics, bridging the gap between fundamental discoveries and real-world applications.