Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

Gordana Dukovic

Second Advisor

Niels Damrauer

Third Advisor

David Jonas

Fourth Advisor

Joel Eaves

Fifth Advisor

Paul King

Abstract

The use of photoexcited electrons and holes in semiconductor nanocrystals as reduction and oxidation reagents is an intriguing way of harvesting photon energy to drive chemical reactions. This dissertation describes research efforts to understand the photoexcited charge transfer kinetics in complexes of colloidal CdS nanorods coupled with either a water oxidation or reduction catalyst. The first project focuses on the charge transfer interactions between photoexcited CdS nanorods and a mononuclear water oxidation catalyst derived from the [Ru(bpy)(tpy)Cl]+ parent structure. Upon excitation, hole transfer from CdS oxidizes the catalyst (Ru2+→Ru3+) on a 100 ps – 1 ns timescale. This is followed by a 10 – 100 ns electron transfer that reduces the Ru3+ center. The relatively slow electron transfer dynamics may provide opportunities for accumulation of the multiple holes at the catalyst, which is necessary for water oxidation. The second project details the electron transfer kinetics in complexes of CdS nanorods coupled with [FeFe]-hydrogenase, which catalyzes H+ reduction. These complexes photochemically produce H2 with quantum yields of up to 20%. The kinetics of electron transfer from CdS nanorods to hydrogenase play a critical role in the overall photochemical reactivity, as the quantum efficiency of electron transfer defines the upper limit on the quantum yield of H2 generation. For optimized complexes, the electron transfer rate constant and the electron relaxation rate constant in CdS nanorods are comparable, with values of ≈107 s1, resulting in a quantum efficiency of electron transfer of 42%. Insights from these time-resolved spectroscopic studies are used to discuss the intricate kinetic pathways involved in photochemical H2 generation in photocatalytic complexes. Finally, experimental results from photodriven H2 generation and measurements of nanocrystal excited state lifetimes when the length of the nanocrystal-surface ligand was varied provide a deeper understanding into the mechanism for electron transfer from photoexcited nanorods to hydrogenase.

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