Facile one-pot synthesis of white emitting gold nanocluster solutions composed of red, green and blue emitters

Gold nanoclusters (AuNCs) have emerged as a new class of stable and biocompatible photo-emitters. While red emitting clusters comprising ca. 20-25 Au atoms are readily synthesized by several methods, smaller clusters with higher energy luminescence are much less commonly reported. Here, we report on a straightforward one-step synthesis of red, green, blue and violet emitting AuNCs under mild conditions. Produced in pure ethylene glycol, the structural and optical properties of AuNCs are tuned by adding either aniline or indole. By combining high-resolution TEM, electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and photoluminescence spectroscopy, we identify Au6 (blue), Au11 (green) and Au22 (red) in solutions produced with aniline. This tricolor mixture produces a pure white luminescence under broadband excitation. Au5 (violet) and Au7 (blue) produced with indole exhibit a large 27% quantum yield making them among the brightest blue emitting gold clusters. Importantly, when AuNCs are capped with a thiopegylated ligand shell bearing a terminal carboxylate, amine or biotin, they become water soluble and stable while preserving intact their photo-physical characteristics. This work provides an easy access to robust emitters with tunable fluorescence and surface functionality for potential use in biolabelling, hyperspectral sensing or display technology.