Atom-precise coinage metal nanoclusters for near-infrared emission: excited-state dynamics and mechanisms

Understanding the excited-state dynamics of atomically precise coinage metal nanoclusters (CMNCs) is pivotal for elucidating their photoluminescence (PL) mechanisms and rationally tuning emission properties-particularly in the near-infrared (NIR) region, where CMNC-based nanomaterials have tremendous potential for biomedical and optoelectronic applications. This review presents a systematic and comprehensive account of recent advances in investigating the excited-state dynamics and PL mechanisms of NIR-emitting CMNCs with atomic precision, leveraging the synergistic integration of time-resolved spectroscopy and time-dependent density functional theory (TD-DFT) calculations. Distinct from previous reviews that offer a broad survey of CMNC properties, the present review focuses specifically on intrinsic factors, highlighting molecular vibrational features and electronic structure modulation as key determinants of NIR emission. We begin by outlining how time-resolved spectroscopic techniques-including femtosecond and nanosecond transient absorption (fs-/ns-TA) and time-resolved fluorescence spectroscopy (TRFS)-coupled with TD-DFT modeling, facilitate the probing of relaxation dynamics, photophysical behaviors, and the underlying electronic structures of CMNCs. We then highlight how these advanced techniques reveal the role of coherent oscillations and excited-state relaxation in dictating PL efficiency and characteristics, while delving into strategies such as ligand rigidification, metal doping, kernel engineering, and induced structural transformations that suppress non-radiative decay pathways and thereby enhance NIR PL quantum yield (PLQY) in the NIR region. Finally, we conclude by discussing the current challenges and future opportunities in deepening our understanding of optical properties and excited-state dynamics of NIR-emitting CMNCs, underscoring the imperative for advanced experimental methodologies and rational design strategies to optimize their functionalities for emerging applications.