Structural effects on photoinduced electron transfer in carotenoid-porphyrin-quinone triads

Darius Kuciauskas, Paul A. Liddell, Su Chun Hung, Su Lin, Simon Stone, Gilbert R. Seely, Ana L Moore, Thomas A Moore, John Devens Gust

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Abstract

meso-Polyarylporphyrins are often used as components of molecules that mimic photosynthetic reaction centers by carrying out photoinduced electron-transfer reactions. Studies of these systems have raised questions concerning the role of alkyl substituents at the "β-pyrrolic" positions on the porphyrin periphery in limiting π-π overlap between the macrocycle and the aryl rings. The degree of overlap affects electronic coupling and, therefore, the rates of electron-transfer reactions. There is also evidence that when the linkages joining porphyrins to electron-acceptor or -donor moieties contain amide bonds, the sense of the amide linkage may strongly affect electron-transfer rate constants. In this study, three carotenoid-porphyrin-quinone molecular triads and various model compounds have been prepared, and electron-transfer has been studied using time-resolved emission and absorption techniques. The results show that steric hindrance due to methyl groups at the β-pyrrolic positions reduces electron-transfer rate constants by a factor of ∼1/5. In addition, amide-containing donor-acceptor linkages having the nitrogen atom attached to the porphyrin meso-aryl ring demonstrate electron-transfer rate constants ∼30 times larger than those for similar linkages with the amide reversed, after correction for thermodynamic effects.

Original languageEnglish
Pages (from-to)429-440
Number of pages12
JournalJournal of Physical Chemistry B
Volume101
Issue number3
Publication statusPublished - Jan 16 1997

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Engineering(all)

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