Acta Phys. -Chim. Sin. ›› 2018, Vol. 34 ›› Issue (7): 792-798.

Special Issue: 原子水平上精确控制纳米簇和纳米粒子

• ARTICLE •

### PPh3: Converts Thiolated Gold Nanoparticles to [Au25(PPh3)10(SR)5Cl2]2+

Min ZHU1,2,Manbo LI1,Chuanhao YAO1,Nan XIA1,Yan ZHAO1,2,Nan YAN1,Lingwen LIAO1,Zhikun WU1,*()

1. 1 Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanotechnology, CAS Center for Excellence in Nanoscience, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, P. R. China
2 University of Science and Technology of China, Hefei 230026, P. R. China
• Received:2017-09-12 Published:2018-03-26
• Contact: Zhikun WU E-mail:zkwu@issp.ac.cn
• Supported by:
the National Natural Science Foundation of China(21222301);the National Natural Science Foundation of China(21528303);the National Natural Science Foundation of China(21603234);the National Natural Science Foundation of China(21771186);the National Natural Science Foundation of China(21171170);the National Natural Science Foundation of China(21601193);the National Basic Research Program of China(2013CB934302);the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology(2014FXCX002);the CAS/SAFEA International Partnership Program for Creative Research Teams

Abstract:

Research on gold nanoclusters is at the frontier of nanoscience and nanotechnology. The introduction of the first phosphine-protected gold nanocluster, Au11(PPh3)7(SCN)3 (where PPh3 stands for triphenylphosphine and Ph stands for benzene), can be dated back to 1969. As research in the field progressed, many structures of phosphine-protected nanoclusters such as Au5, Au8, Au13, and Au39 were reported. However, the stability of these phosphine-protected nanoclusters was not satisfactory, which handicapped their research and application. In an attempt to find alternatives for phosphine-protected nanoclusters, thiolated gold nanoclusters have attracted extensive attention in recent years. So far, there has been great progress primarily owing to the development of wet-chemical synthesis techniques, among which the utilization of ligand-exchange has been proved to be very effective to synthesize thiolated gold nanoclusters. It can be easily understood that phosphine in gold nanoclusters can be exchanged with thiolate because the latter has stronger affinity for gold. However, we recently found that the reverse ligand-exchange, i.e., the exchange of thiolate with phosphine, can also take place. Some questions have naturally arisen: Is the reverse ligand-exchange only applicable to superatomic [Au25(SR)18] (SR: thiolate) nanoclusters? Can it occur in other thiolated gold nanoclusters? If so, is this reverse ligand-exchange also dependent on the starting nanoclusters? These intriguing issues have inspired us to conduct this work.

We investigated the reactions of PPh3 with some thiolated gold nanoparticles, including [Au23(SC6H11)16], Au24(SC2H4Ph)20, Au36(TBBT)28 (where TBBT stands for 4-(tert-butyl) benzene-1-thiolate), Au38(SC2H4Ph)20, mixed nanoclusters, and 3 nm Au nanoparticles. Surprisingly, the experimental results showed that under the action of PPh3, thiolated gold nanoclusters (or nanoparticles) with different compositions, structures, sizes, and protecting thiolates can be uniformly transformed to [Au11(PPh3)8Cl2]+ and then [Au25(PPh3)10(SR)5Cl2]2+. In other words, PPh3 is a universal converter for these thiolated gold nanoparticles. However, gold nanoparticles that are protected by polyvinylpyrrolidone (PVP) or citrate and [Ag25(SPhMe2)18] particles cannot be transformed to [Au25(PPh3)10(SR)5Cl2]2+ and [Ag25(PPh3)10(SR)5Cl2]2+, respectively, under the same conditions, which indicated that the special reactivity with PPh3 is unique to thiolated gold nanoparticles. Our preliminary investigation on a possible reaction path between thiolated gold nanoparticles and PPh3 also revealed that the peeling process found in Au25 nanoclusters may be applicable to the conversion of [Au23(SC6H11)16], but not other nanoclusters like Au24(SC2H4Ph)20 and Au36(TBBT)28.

Employing this special chemistry, we synthesized seven [Au25(PPh3)10(SR)5Cl2]2+ species with various ligands and investigated the effect of the ligand on the luminescence properties of [Au25(PPh3)10(SR)5Cl2]2+. We found that the luminescence quantum yields decreased in the following order: [Au25(PPh3)10(SCH2Ph-t-Bu)5Cl2]2+ (1.32 × 10−4) > [Au25(PPh3)10(SCH2Ph)5Cl2]2+ (8.23 × 10−5) > [Au25(PPh3)10(SC2H4Ph)5Cl2]2+ (5.35 × 10−6) > [Au25(PPh3)10(SC12H25)5Cl2]2+ (5.02 × 10−6) > [Au25(PPh3)10(SPh-t-Bu)5Cl2]2+ (3.97 × 10−6) > [Au25(PPh3)10(SC6H13)5Cl2]2+ (3.73 × 10−6) > [Au25(PPh3)10(S-c-C6H11)5Cl2]2+ (1.53 × 10−6). Therefore, it can be concluded that SCH2Ph-t-Bu is the best ligand, while S-c-C6H11 is the worse one for triggering luminescence from gold nanoparticles in the investigated thiolates.

Since such diversity in surface ligands is not found in other nanoclusters (e.g., [Au25(SR)18]), the special chemistry between thiolated gold nanoparticles and PPh3 provides excellent opportunities to investigate the effect of ligands on the properties of gold nanoparticles and to screen ligands for special applications.

In summary, in this work we reveal the unique chemistry of thiolated gold nanoparticles with PPh3 and provide excellent opportunities for investigating ligand effects of gold nanoparticles and screening ligands for special applications.

MSC2000:

• O648