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Dirk M. Guldi
University of Cologne, Germany, B.S. ('85) M.S. ('88) Ph.D. ('90)
Tel. (574) 631-7441
Reactive Intermediates and Photoexcited States

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.



Supported by the Division of
Chemical Sciences
Office of
Basic Energy Sciences
at the
U.S. Department of Energy

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Last Modified: 06/28/2010



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