Chapter 13 - Tailoring Functionality of Clusters and Their Complexes with Biomolecules by Size, Structures, and Lasers

Abstract

Theoretical investigation of structural, optical, reactivity, and dynamical properties of free clusters and clusters interacting with different environments such as surfaces and isolated biomolecules is presented. We first present the study of the optical properties of silver clusters supported on the MgO surfaces and compare them with the optical properties of hybrid silver-cluster biomolecule systems. The mechanisms responsible for the interactions between different subunits have been determined. The role of support is to shift the absorption and emission properties of pure silver cluster in the visible regime. In contrast, in the case of biomolecule-cluster hybrid systems, enhancement of either the absorption or the emission can be induced depending on the structure and cluster size because of the interaction of excitations between two subunits. Our findings provide fundamental insight necessary for the development of efficient photoemissive centers with possible applications for optical data storage and biosensing. In the context of cluster reactivity, we propose to introduce intrinsic dynamical properties as a new criterion for promoting reactivity of small noble metal clusters relevant for heterogenous catalysis. We demonstrate that the very different nature of the internal vibrational energy redistribution (IVR) such as dissipative or resonant IVR between cluster and adsorbate leads to large and low sticking probabilities for molecular oxygen on silver and gold clusters, respectively, thus promoting reactivity only in the case of gold. Furthermore, we show that femtosecond time-resolved photoelectron spectroscopy (TRPES) in combination with ab initio molecular dynamics (MD) “on the fly” can be used to study the relaxation dynamics of optically excited states in anionic gold clusters (Au n − , n = 5–8). Our results show that the nature of the excited state dynamics strongly depends on the size and structures of the clusters in the size regime in which “each atom counts.” Finally, we present our new strategy for the optimal control of ground state dynamics with shaped IR-pulses on the basis of the semiclassical Wigner distribution approach applicable to complex systems. The scope of the strategy is demonstrated on two prototype examples for rigid and floppy molecules: isomerization of the Na 3 F cluster and the glycine molecule. In the case of Na 3 F, isomerization is single mode selective. In contrast, a larger number of modes are participating in the control of the isomerization process of glycine. We show that from the shaped IR pulses a fundamental insight about processes underlying the optimal control can be gained. Altogether, we demonstrate the role of theory in establishing conditions under which different processes can be experimentally observed or controlled with the aim to stimulate new experiments in the fields bridging cluster science and nanotechnology.