Ultrafast Dynamics in Nanomaterials: From Gold Clusters to Dye-Sensitized Semiconductors

Femtosecond resolved "pump-probe" spectroscopic experiments are utilized to probe energy and charge transport mechanisms in a variety of synthetic nanomaterials systems. These systems range from applied materials synthesized for use in solar energy conversion devices (π-conjugated polymers and dye sensitized semiconductors) to materials prepared for more fundamental research ("quantum-sized" gold nanoclusters). Because all quantum mechanical rate models are effectively derivatives of Fermi's Golden Rule, the observed energy and charge transfer dynamics in all systems are discussed in various contexts of this famous rate law. In addition, reduced descriptions of the rate law that are more suitable to the condensed phase systems studied herein are introduced.;Marcus theory of electron transfer is used extensively in the study of both intramolecular and intermolecular electron transfer mechanisms in osmium and ruthenium polypyridyl dye complexes both in neat solution and complexed with TiO2 semiconductor nanoparticles. These electron transfer events were observed to occur on the femtosecond to picosecond timescale in all systems. Picosecond energy transfer events observed in a newly synthesized π-conjugated polymer in the form of exciton "hopping" are discussed in the framework of Förster theory. In addition, sub-picosecond electron transfer from the pure polymer to electron accepting dopants (PCBM) is observed, where the quantum yield is strongly dependent on the microscopic structure of the system. Finally, femtosecond and picosecond energy transfer events in the form of interval conversion between core and semiring ligand localized excited states are observed in two novel gold nanocluster systems, whose < 2 nm size allows them to exhibit molecule-like electronic properties.;For all systems, energy and charge transport dynamics/mechanisms are experimentally investigated using the specialized "pump-probe" spectroscopic technique known as transient grating. Although providing equivalent information to more conventional techniques such as transient absorption, the transient grating technique has many advantages over the former including background free signals and the ability to use extremely low laser fluences. In addition, the use of multiple laser beams to excite and probe samples allows for direct experimental control over all field matter interactions with the samples, which allows one to probe dynamics that would otherwise be unobservable.