Mimicry of carotenoid photoprotection in artificial photosynthetic reaction centers: Triplet-triplet energy transfer by a relay mechanism

Devens Gust, Thomas A. Moore, Ana L. Moore, Darius Kuciauskas, Paul A. Liddell, Brian D. Halbert

Research output: Contribution to journalArticlepeer-review

69 Citations (Scopus)

Abstract

Two artificial photosynthetic reaction centers consisting of a porphyrin (P) covalently linked to both a carotenoid polyene (C) and a fullerene derivative (C60) have been prepared and found to transfer triplet excitation energy from the fullerene moiety of C-P-3C60 to the carotenoid polyene, yielding 3C-P-C60. The transfer has been studied both in toluene at ambient temperatures and in 2-methyltetrahydrofuran at lower temperatures. The energy transfer is an activated process, with E(a) = 0.17 eV. This is consistent with transfer by a triplet energy transfer relay, whereby energy first migrates from C-P-3C60 to the porphyrin, yielding C-3P-C60 in a slow, thermally activated step. Rapid energy transfer from the porphyrin triplet to the carotenoid gives the final state. Triplet relays of this sort have been observed in photosynthetic reaction centers, and are part of the system that protects the organism from damage by singlet oxygen, whose production is sensitized by chlorophyll triplet states. The fullerene-containing triads can also demonstrate stepwise photoinduced electron transfer to yield long-lived C.+-P-C60.- charge-separated states. Electron transfer occurs even at 8 K. Charge recombination of C.+-P-C60.- yields 3C-P-C60, rather than the molecular ground state. These photochemical events are reminiscent of photoinduced electron transfer in photosynthetic reaction centers.

Original languageEnglish
Pages (from-to)209-216
Number of pages8
JournalJournal of Photochemistry and Photobiology B: Biology
Volume43
Issue number3
DOIs
Publication statusPublished - Jun 1 1998

Keywords

  • Carotene
  • Energy transfer
  • Photosynthesis
  • Porphyrin
  • Triplet

ASJC Scopus subject areas

  • Radiation
  • Radiological and Ultrasound Technology
  • Biophysics
  • Radiology Nuclear Medicine and imaging

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