Understanding Energy and Electron Transfer in Multi-Metal Coordination Compounds

University Of Florida, Gainesville FL

Investigators

Abstract

The Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division supports the work of Professor Valeria Kleiman at the University of Florida to investigate the properties of a class of organometallic molecules that show promise as solar-energy harvesters or conduits for electron motion (molecular wires). Organometallic molecules consist of an organic component (mostly carbon and hydrogen atoms) and metal atoms which play a key role in how the molecules interact with light. The main focus of this project is to understand the first steps following absorption of light, how the energy is transported through the different molecular architectures and how the structure of the molecules can help enhance and control the energy transport process. This project involves tuning the electronic properties of the molecules by varying the kinds of metal atoms used or the nearby organic structures (called "ligands") to which the metal atoms are attached. By observing how energy and electrons move through molecules after they are exposed to light, the Kleiman research team can provide the fundamental information that will be needed to develop efficient solar energy capture and transport systems based on organometallic molecules. It is noted that energy and electron transfer processes in organometallic ssytems occur in very fast time scales (a millionth of a millionth of a second). Thus, these studies utilize ultrafast laser spectroscopy tools, including the use of multidimensional spectroscopies developed in the Kleiman laboratory. The project aims at fundamental understanding of the excited state dynamical parameters leading to photoinduced energy transfer, photoinduced-multielectron-redox reactions, and their competition, as they are modulated by the nature of the metal center and the organic ligands. A major question to answer is the role of vectorial energy transfer vs potential delocalization of the excited states. Within this context the project opens a new venue for the exploration of excited state dynamics and couplings of cyano-bridged metallo-dimers, oligomers and nanoparticles using ultrafast broadband Transient Absorption Spectroscopy combined with 2-Dimensional Electronic Spectroscopy to explore the initial steps following photoexcitation in multi-metal architectures with organic ligands that allow the modulation of their HOMO-LUMO gaps and state couplings. The investigations will include assemblies of increased complexity where the photophysics can be modulated by the orientation of different organic ligands, and where metal centers are covalently bound through NC bridges whose own orbitals cannot trap the excitation but can open coupling-channels between different centers. The broader impact of this project includes the internationalization of graduate education through the collaboration with a laboratory in the University of Buenos Aires (Argentina). Additionally, undergraduate, graduate and postdoc students will learn to use state of the art tools and become proficient in recent spectroscopy technological advances preparing them for careers in industry and/or academia. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.