Thiolate-protected atomically precise gold nanoclusters exhibit molecular properties owing to the quantum confinement effect, originating from the ultra-small size of the nanoclusters. The unique characteristics of gold nanoclusters such as large surface area, optical features, and chirality, enable their applications in catalysis, bioimaging, sensing and so on. Additionally, the core-shell structure of the nanocluster, with the metal kernel enveloped by a monolayer of organic ligands, provides the feasibility to manipulate the metal core and surface ligands, thereby optimizing the physicochemical properties to suit specific objectives.
First, we realized the precise manipulation of ligand chemistry on Au25PET18 nanoclusters. Exactly one monothiol functionalized metal-terpyridine complex (metal= Ru, Co, Ni, Fe) is added or exchanged to neutral Au25PET18 nanoclusters through ligand exchange reactions, forming Au25PET18(metal complex)1 and Au25PET17(metal complex)1, respectively. This phenomenon stands out as unique in contrast to common ligand exchange reactions, in which the number of exchanged ligands is typically uncontrollable and incoming ligands can only substitute the existing surface ligand without addition to the parent nanoclusters. We observed that the selective ligand exchange or ligand addition depends on the oxidation properties of metal complexes and charge state of parent Au25PET18 nanocluster. The photoluminescence quantum yield of Au25PET18(Ru complex)1 is 14 times higher than that of pristine Au25PET18.
In addition, Au25 nanocluster can serve as a photosensitizer due to its discrete energy bands. Photocoupled electrocatalytic CO2 reduction (PECR) was investigated using various metal complexes anchored Au25 nanoclusters, [Au25PET17(metal complex)1, abbreviated as Au25-M]. The anchoring of Ru and Ni complexes on Au25 nanoclusters (Au25−Ru and Au25−Ni) leads to adequate CO2 to CO conversion for photocoupled PECR in terms of high selectivity, with Faradaic efficiency of CO (FECO) exceeding 90 % in a wide potential range, remarkable activity (CO production rate up to two times higher than that for pristine Au25PET18) and extremely large turnover frequencies (TOFs, 63012 h−1 at −0.97 V for Au25−Ru and 69989 h−1 at −1.07 V vs. RHE for Au25−Ni). Moreover, PECR stability test indicates the excellent long-term stability of the modified nanoclusters in contrast with pristine Au nanoclusters. These improvements are attributed to more active sites and an efficient electron transfer pathway provided by the metal complexes. It provides a new strategy for designing active and stable nanoclusters for different photo/electrocatalytic applications.
The self-assembly of gold nanoclusters induced by ligand exchange reaction is often plagued by uncontrollability and instability, leading to the formation of oligomer mixtures. In this thesis, we successfully achieved the precise dimeric assembly of gold nanoclusters linked by dithiol functionalized metal-terpyridine complexes (metal = Ni, Fe), based on our observation of controllable ligand exchange on Au25 nanoclusters. Additionally, we investigated the photophysical properties of these assemblies. This study offers a guide for the precise assembly of metal nanoclusters into dimers.
