Two triplet emitting states in one emitter: Near-infrared dual-phosphorescent Au20 nanocluster

Intrinsic dual-emission (DE) of gold nanoclusters in the near-infrared (NIR) are fascinating for fundamental im-portance and practical applications, but their synthesis remains a formidable challenge and sophisticated excited-state processes make elucidating DE mechanisms much more arduous. Here, we report an all-alkynyl-protected gold nanocluster, Au20, showing a prolate Au12 tri-octahedral kernel surrounded by two Au2(CZ-PrA)3 dimers, four Au(CZ-PrA)2 monomers, and two CZ-PrA- bridges. Au20 exhibits distinguished pho-tophysical properties including NIR DE at 820 and 940 nm, microsecond radiative relaxation, and 6.26% photo -luminescent quantum yield at ambient environment in nondegassed solution. Combining systematic studies on steady/transient spectroscopy and theoretical calculation, we identified two triplet charge transfer (CT) states, ligand-to-kernel and kernel-based CT states as DE origins. Furthermore, this NIR DE exhibits highly independent and sensitive response to surrounding environments, which well coincide with its mechanism. This work not only provides a substantial structure model to understand a distinctive DE mechanism but also motivates the further development of NIR DE materials.

Automated summary

In this study, an all-alkynyl-protected gold nanocluster, Au20, with distinguished photophysical properties including near-infrared dual-emission (DE) at 820 and 940 nm and high photo-luminescent quantum yield, was synthesized. Through systematic spectroscopic and theoretical studies, two triplet charge transfer states, ligand-to-kernel and kernel-based CT states, were identified as the origins of DE. The NIR DE also exhibited highly independent and sensitive responses to surrounding environments. This work provides insights into the DE mechanism and promotes the development of NIR DE materials.