Francisco Hidalgo

Ab Initio Electronic Circular Dichroism of Fullerenes, Single‐Walled Carbon Nanotubes, and Ligand‐Protected Metal Nanoparticles

The versatility and applicability of a time-perturbed density functional method implemented within the SIESTA program package to calculate electronic circular dichroism of diverse nanoparticles is discussed. Results for nanostructures, such as fullerenes, single-wall carbon nanotubes, as well as metallic nanoparticles composed of up to hundreds of atoms were examined by comparison with previously reported experimental and theoretical results. In all cases, the calculated electronic circular dichroism shows very good consistency with other calculations, and a remarkable agreement with experiments. It is concluded that such a high-level method provides theoretical support for the quantification, understanding, and prediction of chirality and its measurement in nanostructures. It is expected that this information would be useful to motivate further experimental studies and interpretation of optical activity in terms of electronic circular dichroism in novel nanostructures.

Optical activity of achiral ligand SCH3 adsorbed on achiral Ag55 clusters: relationship between adsorption site and circular dichroism.

The electronic circular dichroism (CD) spectra of a methyl-thiol adsorbed at different sites on an icosahedral silver nanoparticle is studied by using time-perturbed density functional theory. Despite that separately molecule and nanoparticle are achiral and consequently optically inactive, the Ag(55)-SCH(3) compound emerges with a new symmetry, which may be chiral or not depending on the adsorption site and orientation of the molecule. It is found that chirality is favored when the thiol is adsorbed between two atoms of different coordination number. Chiral compounds have characteristic CD spectra in the UV-visible region, where Ag(55) shows optical absorption but SCH(3) does not; revealing that highly degenerated molecular-like electronic states of Ag(55) are modified by the presence of the molecule inducing optical activity. It is concluded that CD line-shapes and magnitude strongly depend on the site where the adsorption takes place, while its intensity is modulated by the molecule orientation.

On the stability of noble-metal nanoclusters protected with thiolate ligands*

Noble metal nanoclusters (NCs) protected with thiolate ligands have been of interest because of their long-term stability that makes them suitable as building blocks for diverse assembled systems with emergent and improved functions. Despite the advances in synthesis and characterization, the mechanisms that contribute to their stability are still poorly understood. In this article, we review the different criteria that have been used to explain the experimental stability of NCs with a well-defined number of atoms that are protected with thiolate ligands. We discuss why these criteria are not enough to explain the stability. We conclude that there are other physical factors that should be included when explaining the stability of these systems and could be important for the discovery of new noble-metal NCs.