Intramolecular electron transfer through the 20-position of a chlorophyll a derivative: An unexpectedly efficient conduit for charqe transport

Richard F. Kelley, Michael J. Tauber, Michael R Wasielewski

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Abstract

Suzuki cross-coupling reactions have afforded 20-phenyl-substituted Chlorophyll a derivatives (ZCPh) in good yields and significant quantities from readily available Chl a. A series of donor-acceptor dyads was synthesized in which naphthalene-1,8:4,5-bis(dicarboximide) or either of two perylene-3,4:9,10-bis(dicarboximide) electron acceptors is attached to the para position of the 20-phenyl group. Comparisons with the analogous dyads based on a zinc 5,10,15-tri(n-pentyl)-20-phenylporphyrin donor show that, for a given acceptor and solvent, the rates of photoinduced charge separation and recombination as well as the calculated electronic coupling matrix elements, V, for these reactions differ by less than a factor of 2. However, EPR and ENDOR spectroscopy corroborated by DFT calculations show that the highest occupied MO of ZCPh+. has little spin (charge) density at the 20-carbon atom, whereas Z3PnPh+. has significant spin (charge) density there, implying that V, and therefore the electron-transfer rates, should differ significantly for these two macrocyclic donors. DFT calculations on ZCPh +. and Z3PnPh+., with two -0.5 charges located where the nearest carbonyl oxygen atoms of the acceptor would reside in the donor-acceptor dyads, show that the presence of the negative charges significantly shifts the charge density of both ZCPh+. and Z3PnPh+. from the macrocycle onto the phenyl rings. Thus, the presence of adjacent covalently linked radical anions at a fixed location relative to each of these radical cations results in nearly identical electronic coupling matrix elements for electron transfer and therefore very similar rates.

Original languageEnglish
Pages (from-to)4779-4791
Number of pages13
JournalJournal of the American Chemical Society
Volume128
Issue number14
DOIs
Publication statusPublished - Apr 12 2006

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Chlorophyll
Charge density
Electrons
Derivatives
Discrete Fourier transforms
Perylene
Atoms
Cross Reactions
Electron Spin Resonance Spectroscopy
Naphthalene
Genetic Recombination
Anions
Paramagnetic resonance
Cations
Zinc
Spectrum Analysis
Negative ions
Carbon
Positive ions
Spectroscopy

ASJC Scopus subject areas

  • Chemistry(all)

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Intramolecular electron transfer through the 20-position of a chlorophyll a derivative : An unexpectedly efficient conduit for charqe transport. / Kelley, Richard F.; Tauber, Michael J.; Wasielewski, Michael R.

In: Journal of the American Chemical Society, Vol. 128, No. 14, 12.04.2006, p. 4779-4791.

Research output: Contribution to journalArticle

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