Atomically precise metal nanoclusters (MNCs) composed of a few to hundreds of metal atoms represent an emerging class of nanomaterials with a precise composition. With the size approaching the Fermi wavelength of electrons, their energy levels are well-separated, leading to molecule-like properties, like discrete single electronic transitions, tunable photoluminescence (PL), inherent structural anisotropy, and distinct redox behavior. Extensive synthetic efforts and electronic structure revelation have expanded applicability of MNCs in catalysis, optoelectronics, and biology. This review highlights the intriguing photophysical and electrochemical behaviors of MNCs and their regulatory parameters and applications. Initially, we present a brief discussion on the evolution of MNCs from gas-phase naked metal clusters to monolayer ligand-protected MNCs along with representative studies on their electronic structure. Due to their quantized molecular orbitals, they often exhibit PL, which can be regulated based on their capping ligands, number of atoms, crystal packing, presence of heterometal, and surrounding environment. Apart from PL, the relaxation pathways of MNCs on an ultrafast time scale have been extensively studied, which significantly differ from that of plasmonic metal nanoparticles. Moreover, their interaction with high-intensity light results in unique non-linear optical properties. The synergy between MNCs in a hierarchical self-assembled structure has been exploited to enhance their PL by precisely tuning their non-covalent interactions. Moreover, several NC-based hybrids have been designed to exhibit efficient electron or energy transfer in the photoexcited state. In the next section, we briefly focus on the redox behavior of NCs and facile electron transfer to suitable substrates, which result in enzyme-like catalytic activity. Utilizing these photophysical and electrochemical behaviors, NCs are widely employed in catalysis, optical sensing, and light-harvesting applications, which are also discussed in this review. In the final section, conclusions and open questions for the NC research community are included. This review will provide a comprehensive view of the emerging physicochemical properties of MNCs, thereby enabling an understanding for their precise modulation in future.

中文翻译：

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对具有新兴光物理特性的原子精确金属纳米团簇的全面综述，适用于各种应用


由几个到数百个金属原子组成的原子精确金属纳米团簇 （MNC） 代表了一类具有精确成分的新兴纳米材料。当电子的大小接近费米波长时，它们的能级被很好地分离，从而产生类似分子的特性，如离散的单电子跃迁、可调谐的光致发光 （PL）、固有的结构各向异性和独特的氧化还原行为。广泛的合成工作和电子结构揭示扩大了 MNC 在催化、光电子和生物学中的适用性。这篇综述重点介绍了 MNC 有趣的光物理和电化学行为及其调控参数和应用。最初，我们简要讨论了 MNC 从气相裸金属簇到单层配体保护的 MNC 的演变，以及对其电子结构的代表性研究。由于它们的量子化分子轨道，它们经常表现出 PL，可以根据它们的加帽配体、原子数、晶体堆积、异金属的存在和周围环境进行调节。除了 PL 之外，MNCs 在超快时间尺度上的弛豫途径也得到了广泛的研究，这与等离激元金属纳米颗粒的弛豫途径明显不同。此外，它们与高强度光的相互作用产生了独特的非线性光学特性。分层自组装结构中 MNC 之间的协同作用已被利用，通过精确调整其非共价相互作用来增强其 PL。此外，已经设计了几种基于 NC 的杂化物，以在光激发态下表现出高效的电子或能量转移。 在下一节中，我们将简要介绍NCs的氧化还原行为和电子向合适的底物的简单转移，从而产生类似酶的催化活性。利用这些光物理和电化学行为，NCs 被广泛用于催化、光学传感和光捕获应用，本文也将对此进行讨论。在最后一部分，包括结论和北卡罗来纳州研究界的开放性问题。本文将全面了解 MNCs 新兴的物理化学性质，从而为将来的精确调控提供帮助。