Synthesis and Enhanced Linear and Nonlinear Optical Properties of Chromophore–Au Metal Cluster Oligomers

Abstract

Using nanoclusters as building blocks for supracrystals can offer unique optical and electronic properties of metal nanoclusters for designing new materials. The advantage of building nanocluster crystals through molecular linkers is that the linker can be used as a functional group for the nanoclusters (e.g., dye−nanocluster systems). In this study, we employed the ligand exchange reaction to synthesize chromophore−Au 25 nanocluster oligomers and investigated their linear and nonlinear optical properties. The chromophore−Au 25 nanocluster oligomers product mixture was separated into four bands by polyacrylamide gel electrophoresis and characterized by matrix-assisted laser desorption ionization mass spectrometry and scanning transmission electron microscopy imaging. The linear optical properties of the systems were investigated by steady state UV−vis absorption and fluorescence spectroscopy. The chromophore−Au 25 nanocluster oligomers showed increased oscillator strength and transition dipole moment compared to single Au 25 nanoclusters. Energy transfer from the chromophore 4,4′-thiodibenzenethiol (TBT) to the metal cluster was observed in the chromophore−Au 25 nanocluster dimer system. The excited state and fluorescence dynamics were investigated by transient absorption spectroscopy, time-resolved fluorescence upconversion, and time-correlated single photon counting. The chromophore−Au 25 nanocluster oligomers have a long-lived surface state due to the contribution of energy transfer by two nanocluster cores. The two-photon absorption cross sections of the chromophore−Au 25 nanocluster oligomers showed an increasing enhancement trend with increasing oligomer length. An enhancement factor of up to 68 times was found compared to single Au 25 nanoclusters. Finally, we performed a structure−property correlation analysis to explain the observed optical properties of these systems.

Structure–property relationships on thiolate-protected gold nanoclusters

“…In 1994, Brust et al introduced a synthetic method to create a new class of gold nanoparticles protected by thiolate ligands. 1 Since then, these nanoparticles have attracted tremendous research interest due to their intriguing properties ranging from structural, to optical, to electrochemical, [2][3][4][5][6] giving rise to vast potential for applications in the elds of catalysis, chemical sensing, and biomedicine. 7 A class of these nanoparticles are known as thiolate-protected gold nanoclusters (Au NCs).…”

Metal Nanoclusters as Versatile Building Blocks for Hierarchical Structures

“…In their work, Ho-Wu et al investigated the influence a bridging linker can have on linear and nonlinear optical properties of Au NC oligomers. [6] Watersoluble anionic [Au 25 (SG) 18 ] À (SG = glutathione) clusters were covalently linked with 4,4-thiodibenzenethiol (TBT) in the ligand-exchange reaction to produce a mixture of oligomers which were then separated using polyacrylamide gel electrophoresis (PAGE) technique (Figure 4,a and 4,b). The systematic spectroscopic investigation of the formed multimers showed significant changes in their linear and non-linear properties when compared to the single [Au 25 (SG) 18 ] À clusters.…”

Atomically Precise Metal Nanoclusters: Novel Building Blocks for Hierarchical Structures

“…Whereas the dimers showed no optical coupling, the multimers exhibited hybridized plasmon modes with unexpectedly large red‐shifts, most likely due to electron tunneling through the molecular states of the disulfide bridged. A demonstration of the electronic coupling in a NC dimer has been provided by Ho‐Wu et al [55] . who used the ligand exchange strategy to make oligomers of Au 25 connected with 4,4’‐thiodibenzenethiol (Figure 3).…”

“…Ad emonstration of the electronic coupling in aN Cd imer has been provided by Ho-Wue tal. [55] who used the ligand exchange strategy to make oligomers of Au 25 connected with 4,4'-thiodibenzenethiol ( Figure 3). The linear and nonlinearo pticalp ropertiesp ointed to peculiar energy transfer processes between the chromophore and Au 25, as well as between the linked Au 25 units.M ore recently,aA g 25 dimer was prepared using as the linker ac omplex of ruthenium bipyridyl-4-4'-dithiol, introduced via ligand exchange.…”

“…NC-based dimer. Structureand two-photon excitede missionof chromophore (4,4'-thiodibenzenethiol)-Au 25 NC dimer.The Schemed epicts the nonlinear optical behavioroft he NC dimer.R eproduced with permission from ref [55]. (Copyright 2018,A merican Chemical Society).…”