Blue Luminescence Emitted from Monodisperse Thiolate‐Capped Au₁₁ Clusters

Abstract

Gold clusters (Au n , n = the number of gold atoms in the core) containing less than 200 down to a few atoms have gained great attention in the last decade. [1][2][3][4][5][6][7][8] Because only a few gold atoms are contained in the clusters, the size of the clusters approaches the de Broglie wavelength of the conduction electrons. The density of states is insufficient to merge the valence and conduction bands, which allows discrete cluster energy levels to become possible. As a result, gold clusters are likely to behave as "artificial atoms", showing photoluminescence. The quantum yields (QYs) of the clusters are enhanced by several orders of magnitude compared to that of the bulk gold (QY = 10 À10 ), [9] which gives gold clusters potential applications in sensors and labeling.Organothiolate-monolayer-protected gold products exhibit superb stability against air, long-term storage and concentration extremes. [10,11] Due to their extraordinary stability, the fluorescence emission of thiolate-capped Au clusters, especially prepared via modified Brust methods, has been a focus of intensive research. Au 145 clusters surrounded by a passivating layer of dodecanethiol molecules showed luminescence and a quantum yield of (4.4 AE 1.5) 10 À5 .[12] Photoemission from gold clusters (10-39 Au atoms) protected by glutathione were reported, and the emission efficiencies were in the range of 1 10 À4 to 4 10 À3 .[13] Visible luminescence was emitted from gold clusters with 1.8 nm diameter cores and protected by a monolayer of tiopronin thiolate, with a QY of 0.3 % for 451 nm excitation. [14] These elegant studies have undoubtedly opened up many exciting potential applications for the gold clusters. However, these thiolate-protected gold clusters suffer from low QYs, which have become a major obstacle in practical applications.In general, alkyl-and arylthiols containing no functional groups are chosen as the ligands to protect fluorescent gold clusters in Brust two-phase methods. Herein, in contrast to the reported fluorescent thiolate-protected gold clusters prepared via Brust two-phase procedure, we chose carboxylic-acid-terminated thiolated molecules, 3-mercaptopropionic acid (MPA), as the stabilizing agents, and successfully synthesized Au 11 clusters. Clear blue luminescence was observed from the clusters, and fluorescence quantum yield was 8.6 %. [13] From the detailed peak shape analysis, Tanaka and co-workers have found that the Au 4f core-level spectra consist of two components, which are the inner Au atoms and surface Au atoms bonded to surface thiolates.[15] The AuA C H T U N G T R E N N U N G (4f 7/2 ) peak positions of the surface Au components have been located at a higher binding energy than the corresponding inner components. Most of the Au atoms are located on the surface of clusters. Furthermore, the Au atoms in the clusters donate 5d electrons to the thiolates when capped with strongly interacting thiol molecules.[16] These two factors lead to the AuA C H T U N G T R E N N U N G (4f 7/2 ) binding energies of go...

Luminescent metal nanoclusters: controlled synthesis and functional applications

“…In recent years, employing state-of-the-art quantum chemistry codes, relatively accurate prediction and explanation of the optical properties of a broad range of NCs have been realized [8–12]. A broad range of luminescent metal NCs composed of gold (Au) [5–7, 13–27], silver (Ag) [12, 25–36], copper (Cu) [25, 35, 37, 38], platinum (Pt) [25, 39, 40], bismuth (Bi) [11, 41–45], molybdenum (Mo) [46–48] or mixed metals [49–51] have been successfully fabricated using diverse top-down or bottom-up approaches. Compared with other counterparts, Au and Ag NCs have attracted more attention and have been intensively studied over the past decade.…”

Fluorescent Gold Nanoclusters with Interlocked Staples and a Fully Thiolate‐Bound Kernel

“…[43] However,some Au clusters with green or blue fluorescence have also been described. [44,[46][47][48][49][50] This discrepancy could be due to the fact that the emission wavelength of gold nanoclusters is influenced by multiple factors such as the protecting ligands [46,48] and the …”

Fluorescent Gold Nanoclusters with Interlocked Staples and a Fully Thiolate‐Bound Kernel

“…reported that dihydrolipoic acid protected gold nanoclusters displayed an emission maximum at 700 nm . However, some Au clusters with green or blue fluorescence have also been described . This discrepancy could be due to the fact that the emission wavelength of gold nanoclusters is influenced by multiple factors such as the protecting ligands and the nanocluster size .…”