Effect of coordinated ligands on interporphyrin photoinduced-electron-transfer rates

John Devens Gust, Thomas A Moore, Ana L Moore, H. K. Kang, J. M. DeGraziano, P. A. Liddell, G. R. Seely

Research output: Contribution to journalArticle

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Abstract

The effect of coordination of various pyridines on the rate of photoinduced interporphyrin electron transfer in a molecular dyad consisting of a zinc porphyrin covalently linked to a free base porphyrin moiety has been investigated using time-resolved fluorescence techniques. Coordination of pyridine itself to the zinc ion results in a nearly 30-fold increase in the rate constant for one of the photoinduced-electron-transfer reactions. In similar studies with a series of pyridine ligands bearing substituents with electron-donating or accepting properties, the data correlate well with the substituent constant under the Hammett linear free energy relationship. The reaction constant ρ has a value of -0.35, which indicates that the rate of electron transfer is increased by electron donation to the zinc porphyrin. Electrochemical experiments with a poorly-coordinating electrolyte suggest that this donation stabilizes the interporphyrin charge-separated state, in which the zinc porphyrin moiety is positively charged, and that this stabilization in turn leads to a larger rate constant for electron transfer. Effects of this type undoubtedly play a role in metalloproteins in which a porphyrin metal ion is ligated to the protein. They may also affect the interpretation of solvent effects noted in electron-transfer reactions involving metallated porphyrins.

Original languageEnglish
Pages (from-to)13637-13642
Number of pages6
JournalJournal of Physical Chemistry
Volume97
Issue number51
Publication statusPublished - Jan 1 1993

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porphyrins
Porphyrins
electron transfer
Ligands
ligands
Electrons
zinc
Zinc
pyridines
Pyridine
Rate constants
Bearings (structural)
Metalloproteins
Pyridines
metal ions
electrons
Electrolytes
Free energy
stabilization
Metal ions

ASJC Scopus subject areas

  • Engineering(all)
  • Physical and Theoretical Chemistry

Cite this

Effect of coordinated ligands on interporphyrin photoinduced-electron-transfer rates. / Gust, John Devens; Moore, Thomas A; Moore, Ana L; Kang, H. K.; DeGraziano, J. M.; Liddell, P. A.; Seely, G. R.

In: Journal of Physical Chemistry, Vol. 97, No. 51, 01.01.1993, p. 13637-13642.

Research output: Contribution to journalArticle

Gust, JD, Moore, TA, Moore, AL, Kang, HK, DeGraziano, JM, Liddell, PA & Seely, GR 1993, 'Effect of coordinated ligands on interporphyrin photoinduced-electron-transfer rates', Journal of Physical Chemistry, vol. 97, no. 51, pp. 13637-13642.
Gust, John Devens ; Moore, Thomas A ; Moore, Ana L ; Kang, H. K. ; DeGraziano, J. M. ; Liddell, P. A. ; Seely, G. R. / Effect of coordinated ligands on interporphyrin photoinduced-electron-transfer rates. In: Journal of Physical Chemistry. 1993 ; Vol. 97, No. 51. pp. 13637-13642.
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