Liganded Silver and Gold Quantum Clusters ─ Towards a New Class of Nonlinear Optical Nanomaterials

Metallic quantum clusters belonging to intermediate size regime between two and few hundred of atoms, represent unique building blocks of new materials. Nonlinear optical (NLO) characteristics of liganded silver and gold quantum clusters reveal remarkable features which can be tuned by size, structure and composition. The two-photon absorption cross sections of liganded noble metal quantum clusters are several orders of magnitude larger than that of commercially-available dyes. Therefore, the fundamental photophysical understanding of those two-photon processes in liganded clusters with few metal atoms deserve special attention, in particularly in context of finding the mechanisms responsible for these properties. A broad range of state-of-the-art experimental methods to determine nonlinear optical properties (i.e. two-photon absorption, two-photon excited fluorescence and second harmonic generation) of quantum clusters are presented. The experimental setup and underlying physical concepts are described.
Furthermore, the theoretical models and corresponding approaches are used allowing to explain the experimental observations and simultaneously offering the possibility to deduce the key factors necessary to design new classes of nanoclusters with large NLO properties. Additionally, selected studied cases of liganded silver and gold quantum clusters with focus on their NLO properties will be presented as promising candidates for applications in imaging techniques such as fluorescence microscopy or Second-Harmonic Generation microscopy.

About the Authors:

Dr. Rodolphe Antoine is a Research director at the National Center for Scientific Research (CNRS). His research field is the study of molecular systems of growing complexity in the gas phase. In 1997, he was recruited at CNRS in Lyon for building a molecular beam deflection experiment for electric polarizability measurements on clusters and biomolecules. Most important results on biomolecules are: the first –and unique- measurements of electric dipole of isolated peptides and the first observation of gas phase beta sheets. In 2004, in order to go through larger and more complex systems, his research moved towards laser spectroscopy on trapped biomolecular ions and nanoparticles. He recently focused on the functional role of small silver and gold quantum clusters in model hybrid systems involving peptides in context of new generation of hybrid nanostructured materials for biosensing.

Prof. Dr. Dr. h.c. Vlasta Bonacic-Koutecky is professor of physical and theoretical chemistry in Department of Chemistry, Humboldt-Universitat zu Berlin. Since 2010, she is the Director of the

Interdisciplinary Center for Advanced Science and Technology (ICAST) and since 2014, she is a head of Center of excellence for science and technology - integration of Mediterranean region (STIM) at the University of Split in Croatia. Her major research areas are:

- Theoretical photochemistry and photophysics

- Chemistry and physics of metal clusters and cluster-biomolecule hybrids

- Development of cluster-based catalytic, optical and biosensing materials

- Quantum chemical adiabatic and nonadiabatic molecular dynamics "on the fly" in the frame of TDDFT

- Semiclassical dynamics

- Theory and methods for simulation of time-resolved spectroscopies

- Optimal control and laser selective photochemistry