Gold Nanoclusters: Bridging Gold Complexes and Plasmonic Nanoparticles in Photophysical Properties.

Meng Zhou,Chenjie Zeng,Tatsuya Higaki,Qi Li,Rongchao Jin

doi:10.3390/nano9070933

Abstract

Recent advances in the determination of crystal structures and studies of optical properties of gold nanoclusters in the size range from tens to hundreds of gold atoms have started to reveal the grand evolution from gold complexes to nanoclusters and further to plasmonic nanoparticles. However, a detailed comparison of their photophysical properties is still lacking. Here, we compared the excited state behaviors of gold complexes, nanolcusters, and plasmonic nanoparticles, as well as small organic molecules by choosing four typical examples including the Au10 complex, Au25 nanocluster (1 nm metal core), 13 diameter Au nanoparticles, and Rhodamine B. To compare their photophysical behaviors, we performed steady-state absorption, photoluminescence, and femtosecond transient absorption spectroscopic measurements. It was found that gold nanoclusters behave somewhat like small molecules, showing both rapid internal conversion (<1 ps) and long-lived excited state lifetime (about 100 ns). Unlike the nanocluster form in which metal–metal transitions dominate, gold complexes showed significant charge transfer between metal atoms and surface ligands. Plasmonic gold nanoparticles, on the other hand, had electrons being heated and cooled (~100 ps time scale) after photo-excitation, and the relaxation was dominated by electron–electron scattering, electron–phonon coupling, and energy dissipation. In both nanoclusters and plasmonic nanoparticles, one can observe coherent oscillations of the metal core, but with different fundamental origins. Overall, this work provides some benchmarking features for organic dye molecules, organometallic complexes, metal nanoclusters, and plasmonic nanoparticles.

Highlights

Gold nanomaterials have attracted great interest in both fundamental science and practical applications such as sensing, catalysis, and optoelectronics owing to their unique properties [1,2,3,4,5,6,7,8,9]
For gold nanoparticles with diameters between 3–100 nm, the strong surface plasmon resonance (SPR) dominates in the absorption spectrum, which is caused by collective excitation of free electrons
The structure of a thiolate-protected gold nanocluster typically consists of a metal core with Au–Au bonds (~2.8 Å) and surface Au–S staple motifs [11]

Summary

Introduction

Gold nanomaterials have attracted great interest in both fundamental science and practical applications such as sensing, catalysis, and optoelectronics owing to their unique properties [1,2,3,4,5,6,7,8,9]. The structure of a thiolate-protected gold nanocluster typically consists of a metal core with Au–Au bonds (~2.8 Å) and surface Au–S staple motifs [11]. The Au(I) complexes, on the other hand, do not have a metal core, albeit gold aurophilic interactions (Au···Au distance > 3 Å) often exist owing to the closed-shell d [10] configuration of Au(I) [14,15]. Plasmonic gold nanoparticles (AuNPs), gold nanoclusters, and Au(I) complexes have distinct optical features as a result of their differences in size, structure, and bonding. NanomaPtlearisalms 2o0n19i,c9g, 9o3l3d nanoparticles (AuNPs), gold nanoclusters, and Au(I) complexes have di2sotifn1c3t optical features as a result of their differences in size, structure, and bonding. Tbheehaevleicotrrso.nTahnedelpehctornoonnadndynpahmoincosnardeydniasmcuiscsseadreanddisccuomssepdaraenddincodmetpaailr.eTdhien odbettaaiinl.eTdhreesoublttasinareed orfesgureltast aimrepoorftagnrecaettoimupnodretrasntcaendtothuenirdoeprsttiacanldretshpeoirnsoepatincdalfurerstphoernsperoamndotefuthrtehierrappprolimcaottieontshienir saepnpsilnicgatainodnsoipntiscesn. sing and optics

Materials and Methods

Results and Discussions

Conclusions