On the Stability and Optical Activity of Metallic and Bimetallic Protected Nanoclusters

On the Stability and Optical Activity of Metallic and Bimetallic Protected Nanoclusters

Condensed Matter & AMO Seminar

Date

September 20, 2018 - 2:00pm to 3:00pm

Location

School of Physics - Howey

Room

N110

Affiliation

Universidad Nacional Autonoma de Mexico

Abstract

Some of the main challenges in nanoscience and nanotechnology are the reproducibility and uniformity of the properties of nanostructures. These are crucial for the advancement of this field from the fundamental point of view and future applications. The study of metallic nanoparticles passivated with thiolate ligands has rapidly grown over the last two decades. Synthesis methods have allowed obtaining nanoparticles with a precise number of atoms, which ensures the uniformity and reproducibility of their physical properties.

A large number of atomically exact ligand-protected nanoclusters (NCs) have been fabricated using gold, silver and both species. Here, I analyze the criteria that have been used to explain the experimental stability of metal NCs with a precise number of atoms protected with thiolate ligands. Based on experimental evidence, I show that these criteria are not enough to explain stability and thus, I propose to explore in detail the role of the ligand composition on the stabilization of these NC, which has not been adequately considered.

Additionally, these NCs are good candidates to be used to increase the sensitivity of chiroptical techniques, such as circular dichroism (CD) to characterize chiral molecules. CD signals are tiny in intensity limiting the analysis to samples with large concentrations of chiral molecules, and large enantiomeric excess, being this latter difficult and expensive to achieve. Thus, the increment of the detection limit in chiral spectroscopies would have a significant impact in pure and applied sciences.

It was found that optical activity increases when some chiral molecules are adsorbed in metallic NPs. However, CD signals might significantly differ from that measured of the molecules alone. Although significant, CD response of molecules adsorbed in metallic NPs is yet poorly understood. Here, I want to respond to some open questions. In particular, we investigate how the intrinsic chirality of the molecule, the number of molecules, the specie of the metallic NC, and the induced chiral arrangement of the molecules affect the optical activity in metallic NCs.