Published on Web 07/19/2002
Charge Transport in Photofunctional Nanoparticles
Self-Assembled from Zinc
5,10,15,20-Tetrakis(perylenediimide)porphyrin Building Blocks
Tamar van der Boom, Ryan T. Hayes, Yongyu Zhao, Patrick J. Bushard,
Emily A. Weiss, and Michael R. Wasielewski*
Contribution from the Department of Chemistry and Center for Nanofabrication and
Molecular Self-Assembly, Northwestern UniVersity, EVanston, Illinois 60208-3113
Received March 22, 2002
Abstract: Molecules designed to carry out photochemical energy conversion typically employ several
sequential electron transfers, as do photosynthetic proteins. Yet, these molecules typically do not achieve
the extensive charge transport characteristic of semiconductor devices. We have prepared a large molecule
in which four perylene-3,4:9,10-tetracarboxydiimide (PDI) molecules that both collect photons and accept
electrons are attached to a central zinc 5,10,15,20-tetraphenylporphyrin (ZnTPP) electron donor. This
molecule self-assembles into ordered nanoparticles both in solution and in the solid-state, driven by van
der Waals stacking of the PDI molecules. Photoexcitation of the nanoparticles results in quantitative charge
separation in 3.2 ps to form ZnTPP+PDI- radical ion pairs, in which the radical anion rapidly migrates to
PDI molecules that are, on average, 21 Å away, as evidenced by magnetic field effects on the yield of the
PDI triplet state that results from radical ion pair recombination. These nanoparticles exhibit charge transport
properties that combine important features from both photosynthetic and semiconductor photoconversion
systems.
Introduction
controlling charge transport in organic nanostructures that take
advantage of the speed and efficiency of ultrafast photoinduced
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tectures from functional building blocks. Self-assembly can be
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* Address correspondence to this author. E-mail: wasielew@chem.
northwestern.edu.
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10.1021/ja026286k CCC: $22.00 © 2002 American Chemical Society