Two triplet emitting states in one emitter: Near-infrared dual-phosphorescent Au 20 nanocluster

Abstract

Intrinsic dual-emission (DE) of gold nanoclusters in the near-infrared (NIR) are fascinating for fundamental importance 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 Au 12 tri-octahedral kernel surrounded by two Au 2 (CZ-PrA) 3 dimers, four Au(CZ-PrA) 2 monomers, and two CZ-PrA − bridges. Au20 exhibits distinguished photophysical properties including NIR DE at 820 and 940 nm, microsecond radiative relaxation, and 6.26% photoluminescent 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.