Randolph Thummel
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Randolph Thummel
John and Rebecca Moores Professor
Ph.D., University of California, Santa Barbara, 1971
B.S., Brown University, 1967
Department of Chemistry
University of Houston
Houston, Texas 77204-5003
Office: 5020 - SERC
Phone: 713.743.2734
thummel@uh.edu
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 Organic and Inorganic Chemistry
Our main research interest is the design and synthesis of
novel ligand systems and the careful study of their coordination
chemistry and the properties of their metal complexes. We concentrate
primarily on ligands involving azaaromatic nuclei such as pyridine and
pyrrole (1 – 5). These ligands are synthesized using a wide variety of
techniques ranging from the Friedländer condensation to Stille
couplings. A popular family of ligands involves 2,2'-bipyridine,
terpyridine, and 1,10-phenanthroline. We use steric, conformational,
and electronic effects to modify the properties of these ligands and in
this manner we tune the properties of their corresponding metal
complexes.
Most of our work is aimed at the development of new
photosensitizer molecules for solar energy utilization or biomedical
applications. Our projects fall roughly into three categories and are
funded by three Federal grants as well as a grant from the Robert Welch
Foundation. One project involves using sunlight to photochemically
decompose water into hydrogen and oxygen. We have prepared a series of
dinuclear Ru(II) complexes that, upon exposure to a sacrificial chemical
oxidant (CeIV), very efficiently oxidizes water to dioxygen.
We were surprised to find that this process can be accomplished even
more efficiently by a mononuclear catalyst and we have proposed a
mechanism to explain these observations. Ongoing work is aimed at better
understanding these catalytic processes and also optimizing the
catalyst. Furthermore we hope to drive this reaction with light and are
also examining a corresponding hydrogen evolution catalyst in
collaboration with scientists at Brookhaven National Lab.
A second application for a photosensitizer in solar energy
utilization involves photovoltaics through the design of dye-sensitized
solar cells. We are developing a solid state, combinatorial approach to
the synthesis of photosensitizers directly on the surface of a titanium
dioxide semiconductor. We have also developed new sensitizers based on
1,8-naphthyridine ligands and Bodipy dyes. Thin film solar cells are
constructed and evaluated for their incident photon to current
efficiencies.
A third area of interest involves the interaction of
transition metal complexes with DNA. We are examining two general
classes of complex. The first class involves tridentate analogs of the
intensely studied dppz (dipyridophenazine) molecule (pydppz). We have
found that these complexes bind to DNA by intercalation and demonstrate
the so-called “light switch”
effect. In aqueous environment they are non-luminescent but emit
strongly when bound to DNA. One of these complexes generates singlet
oxygen with nearly 100% efficiency and shows excellent promise as a
photodynamic therapy drug. The second class of complex are diads that
involve a Ru(II) center and a pyrene connected by an ethynyl linkage or a
dinuclear Ru(II) complex. These systems also show photoactivated DNA
mutagenesis and one system appears to interact directly with the DNA
without the involvement of oxygen. These studies are being carried out
in collaboration with two groups at The Ohio State University.
 Our research functions at the interface of many of the more
traditional sub-disciplines of chemistry: organic, inorganic, catalysis,
materials, and biochemistry. Students are trained to deal with a wide
variety of problems using tools such as synthesis, photophysics,
electrochemistry, and biology. More in-depth studies of the systems we
create are often carried out by collaborators all over the world having
more specialized capabilities such as time-resolved spectroscopy, pulse
radiolysis and resonance Raman spectroscopy.
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