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Dirk
M. Guldi
University of Cologne, Germany, B.S. ('85) M.S.
('88) Ph.D. ('90)
Tel. (574) 631-7441
e-mail: guldi.1@nd.edu
Reactive Intermediates and Photoexcited
States
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Scientific
Interests 
Carbon Nanostructures
— charge separation in fullerene and nanotube containing donor-acceptor
systems.
Molecular
Recognition & Biomimetic Motifs — control over the
composition, separation, orientation, and charge-separation in donor-acceptor
ensembles.
Layered
Nanostructures — engineering of extended 1-D, 2-D, or
3-D architectures at the molecular level.
Metallotexaphyrin
— their role in photodynamic and X-ray therapeutic applications.
Recent
Accomplishments
Solvent-dependent conformational changes of a peptide bridge, separating
a ruthenium(II) trisbipyridine donor unit from a fulleropyrrolidine
acceptor unit, is shown to influence the electron transfer process
that occurs in a [Ru(bpy)3]2+-C60
dyad upon photoexcitation. While in CH2Cl2
an intact hydrogen bonding network facilitates charge-separation,
strong protic solvents disrupt the helical secondary structure of
the peptide spacer. Our results strongly support the view that,
upon disruption of the 310-helical structure, the separation
between the two components, C60 and [Ru(bpy)3]2+,
of the dyad tends to increase to a point that disfavors their mutual
electronic interactions. Thus, an unfolding of the 310-helix
leads to a statistically unordered conformation and consequently
to a greater average distance between the two termini.
Several novel molecular donor-acceptor ensembles were probed as
artificial reaction centers. Unquestionably, the most striking but
also puzzling observation is that charge-recombination in zinc porphyrin
/ fullerene dyads and triads is located in the inverted region of
the Marcus parabola, with lifetimes ranging from as short as tens
of picoseconds to nearly seconds. This phenomenon makes these novel
systems particularly appealing for solar energy conversion and photovoltaic
applications, which is currently under intense investigation in
our laboratory. A conceptional breakthrough in our work stems from
recent results regarding a 24% efficient charge-separation within
a molecular tetrad. The lifetime of the spatially-separated (~49
Å) radical pair, product of a sequence of energy and electron
transfer reactions, reaches well beyond milliseconds (0.38 s), into
a time domain which has never been accomplished so far in an artificial
photosynthetic reaction center.
A fascinating concept was illustrated in one of our recent initiatives,
namely, the possibility of organizing structurally different ionic
fullerene derivatives into morphologically different nanoscale composites.
Remarkably, spheres, nanorods, and nanotubules were formed in water
depending on the side chain appendage of the fullerene spheroid.
In fact, the efficient method to fabricate almost perfect and uniformly
shaped nanotubular crystals that order spontaneously opens the way
to the possibility of exploiting the fullerene properties at the
nanometer scale.
Selected Publications
- D.M. Guldi, K.-D. Asmus Electron Transfer from C76
(D2) and C78 (C2v’) to Radical
Cations of Various Arenes; Evidence for the Marcus Inverted Region.
J. Am. Chem. Soc., 1997, 119, 5744.
- A. Polese, S. Mondini, A. Bianco, C. Toniolo, G. Scorrano, D.M.
Guldi, M. Maggini Solvent-Dependent Intramolecular Electron Transfer
in a Peptide-Linked [Ru(bpy)3]2+-C60
Dyad. J. Am. Chem. Soc., 1999, 121, 3456.
- D.M. Guldi, M. Prato Excited States of Fullerene Derivatives.
Acc. Chem. Res., 2000, 33, 695.
- C. Luo, D.M. Guldi, M. Maggini, E. Menna, S. Mondini, N.A. Kotov,
M. Prato Stepwise Assembled Photoactive Films Containing Donor-Linked
Fullerenes. Angew. Chem. Int. Ed., 2000, 39, 3905.
- V. Georgakilas, F. Pellarini, M. Prato, D.M. Guldi, M. Melle-Franco,
F. Zerbetto Supramolecular Self-Assembled Fullerene Nanostructures
Made to Order. Proc. Natl. Acad. Science, 2002, 99, 5075.
- A.A. Mamedov, N.A. Kotov, M. Prato, D.M. Guldi, J.P. Wicksted,
A. Hirsch Molecular Design of Strong SWNT/Polyelectrolyte Multilayers
Composites. Nature Materials, 2002, 1, 190.
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