Directed Self-Assembly of Ultrasmall Metal Nanoclusters

Directed self-assembly (DSA) of nanoparticles plays a key role in customizing advanced functional materials via collective and synergetic properties between neighbored building blocks. In comparison to the blossom of DSA in large (>3 nm) nanoparticle system witnessed in the past decades, the development of DSA in the sub-two-nanometer regime (e.g., underlying chemistry, fundamental properties of assemblies and potential applications) markedly lags behind. Thanks to continuous progress in synthetic chemistry and total structure determination of atomically precise metal nanoclusters (NCs, <2 nm), metal NCs have recently emerged as an ideal platform to uncovering DSA chemistry at this unique sub-nanometer size regime. In addition, recent achievements in DSA chemistry also manifest that DSA represents an alternative means (other than size and composition engineering of individual NC) to customizing molecular-like properties of metal NCs for practical applications. However, ascribed to the small size and large surface energy, linearly extending common nanoscale driving forces into the DSA setups of atomically precise metal NCs is not a trivial task. In this perspective, we systematically summarize recent advances on DSA chemistry in the sub-two-nanometer regime, according to the underlying molecular or nanoscale interactions in the DSA chemistry of metal NCs, including dipolar, van der Waals, electrostatic interactions, hydrogen-bond, template effect, and amphiphilicity. We also discuss evoked or enhanced properties and thus potential applications of metal NCs made possible by DSA. The design principles and governing chemistry of DSA highlighted, here, may add to the acceptance of metal NCs as functional building blocks for construction of hierarchical architectures, which would not only exhibit promising properties for practical applications but also bring about fascinating opportunities for establishing self-assembly chemistry in a broad size regime.