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

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.

Supramolecular Gold Chemistry: From Atomically Precise Thiolate-Protected Gold Nanoclusters to Gold-Thiolate Nanostructures

“…The aim of this Special Issue on "Supramolecular Gold Chemistry" was to provide a unique international forum aimed at covering a broad description of results involving the supramolecular chemistry of gold with a special focus on the gold-sulfur interface leading to hybrid materials, ranging from gold-thiolate complexes, [3] to thiolate-protected gold nanoclusters [4][5][6][7][8][9][10][11] and gold-thiolate supramolecular assemblies or nanoparticles. [12][13][14] The role of thiolates on the structure and optical features of gold nanohybrid systems (ranging from plasmonic gold nanoparticles and fluorescent gold nanoclusters to self-assembled Au-containing thiolated coordination polymers) has been highlighted in the review article by Csapó and coworkers [14].…”

“…The discrete electronic states of nanoclusters cause molecular-like behavior, leading to fascinating physical-chemical properties, such as luminescence, magnetism, and catalysis, etc. Jin and coworkers highlight this molecular-like behavior by thoroughly exploring the differences in the photophysical properties of small organic molecules, gold-thiolate complexes, nanoclusters, and metallic-state nanoparticles [8]. The luminescence properties of 6-aza-2-thio-thymine stabilized gold nanoclusters [9] and gold thiolate coordination polymers [12] demonstrate the high potential of such nanomaterials for bio-sensing or lighting devices.…”

Luminescent metal nanoclusters: Biosensing strategies and bioimaging applications

“…[39] Since there is no bandgap and electron‐hole separation or recombination process in plasmonic metal NPs, they hardly emit light. [40] Nevertheless, as the size of metal NPs decreases, their metallic properties gradually disappear and molecule‐like characteristics become dominant. When the size of MNCs is close to the Fermi wavelength of electrons, the motion of electrons in MNCs is severely restricted, which converts the energy bands of the MNCs into discrete energy levels.…”

Self-Assembled Metal Nanoclusters: Driving Forces and Structural Correlation with Optical Properties

“…MNCs are ultra-small particles consisting of a controlled aggregation of metal atoms protected by a shell of organic ligands. Such MNCs are usually obtained at the atomic precision (i.e., with a defined number of metal atoms (nM) and ligand molecules (mL) leading to formula (M n L m )) and display molecular-like properties [ 15 , 19 , 20 , 21 ]. The geometry of the clusters must be determined by quantum chemistry methods that often use group theory, and the optic response is described in terms of molecular transitions whose positions and intensities are predicted by sophisticated calculations of quantum mechanics [ 22 , 23 , 24 ].…”