Light activated synthesis of the atomically precise fluorescent silver cluster Ag18(Capt)14

Molybdate-Templated Luminescent Silver Alkynyl Nanoclusters: Total Structure Determination and Optical Property Analysis

Two novel MoO42--templated luminescent silver alkynyl nanoclusters with 20-nuclearity ([(MoO42-)@Ag20(C≡CtBu)8(Ph2PO2)7(tfa)2]·(tfa-) (1)) and 18-nuclearity ([(MoO42-)@Ag18(C≡CtBu)8(Ph2PO2)7]·(OH) (2)) (tfa = trifluoroacetate) were synthesized with the green light maximum emissions at 507 and 516 nm, respectively. The nanoclusters were investigated and characterized by single-crystal X-ray crystallography, electrospray ionization mass spectrum (ESI-MS), X-ray photoelectron spectroscopy, thermogravimetry (TG), photoluminescence (PL), ultraviolet-visible (UV-vis) spectroscopy, and density functional theory calculations (DFT). The two nanoclusters differ in their structure by a supplementary [Ag2(tfa)2] organometallic surface motif, which significantly participates in the frontier molecular orbitals of 1, resulting in similar bonding patterns but different optical properties between the two clusters. Indeed, both nanoclusters show strong temperature-dependent photoluminescence properties, which make them potential candidates in the fields of optical devices for further applications.

Accelerated size-focusing light activated synthesis of atomically precise fluorescent Au22(Lys-Cys-Lys)16 clusters

Atomically precise metal nanoclusters are promising candidates for various biomedical applications, including their use as photosensitizers in photodynamic therapy (PDT). However, typical synthetic routes of clusters often result in complex mixtures, where isolating and characterizing pure samples becomes challenging. In this work, a new Au22(Lys-Cys-Lys)16 cluster is synthesized using photochemistry, followed by a new type of light activated, accelerated size-focusing. Fluorescence excitation-emission matrix spectroscopy (EEM) and parallel factor (PARAFAC) analysis have been applied to track the formation of fluorescent species, and to assess optical purity of the final product. Furthermore, excited state reactivity of Au22(Lys-Cys-Lys)16 clusters is studied, and formation of type-I reactive oxygen species (ROS) from the excited state of the clusters is observed. The proposed size-focusing procedure in this work can be easily adapted to conventional cluster synthetic methods, such as borohydride reduction, to provide atomically precise clusters.

Photochemical synthesis of fluorescent Au16(RGDC)14 and excited state reactivity with molecular oxygen

Aqueous metal nanoclusters have emerged as effective materials for biomedical imaging and therapy. Among them, gold nanoclusters (AuNCs) have been widely studied due to their unique electronic structures. These nanoclusters are often optically impure, comprising a mixture of fluorescent clusters with different metal/ligand compositions. The polydispersity of nanoclusters makes it challenging to isolate the most stable structure, and poses further risks for eventual clinical applications. Herein, Au16L14 clusters are reported which are optically pure as assessed by fluorescence excitation-emission matrix (EEM) spectroscopy and parallel factor (PARAFAC) analysis. The reactivity of their excited state with molecular oxygen was also probed, demonstrating that the Au16L14 clusters generate type I reactive oxygen species (ROS), which can make them effective sensitizers for photodynamic therapy.

Anionic Copper Clusters Reacting with NO: An Open-Shell Superatom Cu18. J Phys Chem Lett 2020;11:5807-5814. [PMID: 32597656 DOI: 10.1021/acs.jpclett.0c01643]

Gas-phase metal clusters have been a subject of research interest for allowing reliable strategies to explore the stability and reactivity of materials at reduced sizes with atomic precision. Here we have prepared well-resolved copper cluster anions Cu_n^- (n = 7-37) and systematically studied their reactivity with O₂, NO, and CO. We found remarkable stability of an open-shell cluster Cu₁₈^-, which is comparable with the closed-shell clusters Cu₁₇^- and Cu₁₉^- within the picture of an electronic shell model. Even without having a magic number of valence electrons, intriguingly, the unpaired electron on the singly occupied molecular orbital of Cu₁₈^- is mainly contributed by the central copper atom, while the other 18 delocalized valence electrons occupy the lower-energy superatomic orbitals of the cluster. The finding of such an open-shell superatom Cu₁₈^-, with an electron configuration of 1S²1P⁶1D¹⁰2S¹||1F⁰, is interesting in the sense that an elementary cluster of coinage metal atoms could still behave as a superatom mimicking coinage metals like silver or gold atoms with an empty f orbital. The superatomic stability of this Cu₁₈^- cluster is reinforced by the unique electrostatic interaction between the Cu^- core and Cu₁₇ shell, which provides new insights into the chemistry of metal clusters.