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

Research output: Contribution to journalArticle

94 Citations (Scopus)

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

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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