Nonlinear Optical Properties of Thiolate-Protected Gold Clusters

Abstract

Thiolate-protected gold clusters are promising candidates for imaging applications due to their interesting, size-dependent properties. Their high stability and the ability to functionalize the clusters with biocompatible ligands render the clusters for various imaging techniques such as fluorescence microscopy or Second-Harmonic Generation microscopy. The latter nonlinear optical effect has not yet been observed on this type of ultra-small nanoparticles.We hereby present Second-and Third-Harmonic Generation and multi-photon luminescence of two thiolate-protected gold clusters, Au 25 (SCH 2 CH 2 Ph) 18 and Au 38 (SCH 2 CH 2 Ph) 24 . At a fundamental wavelength of 800 nm, the Au 38 (SCH 2 CH 2 Ph) 24 cluster is active. In contrast, Au 25 (SCH 2 CH 2 Ph) 18 does not yield significant SHG signal. We ascribe this to the center of inversion in the Au 25 cluster. Measurements on chiral Au 25 (capt) 18 (capt: captopril) gave an SHG response, supporting this interpretation. We also observed Third-Harmonic Generation at a fundamental wavelength of 1200 nm. At 800 and 1,100 nm, the clusters decompose after short illumination time, but are stable at illumination at 1,200 nm. This may be exploited in combined deep tissue imaging and photothermal heating for theranostics applications.

Adsorption‐induced Symmetry Distortions in W@Au12 Nanoclusters, Leading to Enhanced Hyperpolarizabilities

“…These properties include magnetic behavior, catalytic reactivity,, optical activity,, and more. A pertinent example is the symmetry‐dependent nonlinear optical activity of thiolate‐protected gold clusters ,…”

Nonlinear Optical Properties of Thiolate-Protected Gold Clusters: A Theoretical Survey of the First Hyperpolarizabilities

“…The chiral cluster has not been crystallized, but from its absorption spectra it seems plausible that the cluster essentially adopts the same structure. The breaking of the symmetry can be proven by two techniques, Circular Dichroism 67 and SHG, 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 We confirm the influence of chiral ligands on a model system. We chose the bidentate 1,1'-binapthyl-2,2'-dithiolate (BINAS).…”

Ligand-protected gold clusters: the structure, synthesis and applications

“…It should be noted that the molecular type of absorption spectrum . UV-Vis spectrum of Au25(SCH2Bn)18 cluster (a) 153 and its interpretation based on the Kohn ± Sham orbitals (b). 11 A is the absorbance.…”