Artificial photosynthetic reaction centers: Mimicking sequential electron and triplet-energy transfer

Rodrigo E. Palacios, Gerdenis Kodis, Stephanie L. Gould, Linda De La Garza, Alicia Brune, John Devens Gust, Thomas A Moore, Ana L Moore

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

An artificial photosynthetic reaction center consisting of a carotenoid (C), a dimesitylparphyrin (P), and a bis(heptafluoropropyl)-porphyrin (P F), C-P-PF, and the related triad in which the central porphyrin has been metalated to give C-PZn-PF have been synthesized and characterized by transient spectroscopy. These triads are models for amphipathic triads having a carboxylate group attached to the PF moiety; they are designed to carry out redox processes across lipid bilayers. Triad C-P-PF undergoes rapid singlet-singlet energy transfer between the porphyrin moieties, so that their excited states are in equilibrium. In benzonitrile, photoinduced electron transfer from the first excited singlet state of P and hole transfer from the first excited singlet state of P F yield the initial charge-separated state C-P.+-P F.-. Subsequent hole transfer to the carotenoid moiety generates the final charge-separated state C.+-P-PF .-, which has a lifetime of 1.1 μs and is formed with a quantum yield of 0.24. In triad C-PZn-PF energy transfer from the PZn excited singlet to the PF moiety yields C-P Zn-1PF. A series of electron-transfer reactions analogous to those observed in C-P-PF generates C .+-PZn-PF.-, which has a lifetime of 750 ns and is formed with a quantum yield of 0.25. Flash photolysis experiments in liposomes containing an amphipathic version of C-PZn-P F demonstrate that the added driving force for photoinduced electron transfer in the metalated triad is useful for promoting electron transfer in the low-dielectric environment of artificial biological membranes. In argon-saturated toluene solutions of C-P-PF and C-P Zn-PF, charge separation is not observed and a considerable yield of triplet species is generated upon excitation of the porphyrin moieties. In both triads triplet energy localized in the PF moiety is channeled to the carotenoid chromophore by a triplet energy-transfer relay mechanism. Certain photophysical characteristics of these triads, including the sequential electron transfer and the triplet energy-transfer relay mechanism, are reminiscent of those observed in natural reaction centers of photosynthetic bacteria.

Original languageEnglish
Pages (from-to)2359-2370
Number of pages12
JournalChemPhysChem
Volume6
Issue number11
DOIs
Publication statusPublished - Nov 11 2005

Fingerprint

Photosynthetic Reaction Center Complex Proteins
Energy transfer
Porphyrins
electron transfer
porphyrins
carotenoids
energy transfer
Carotenoids
Excited states
Electrons
relay
Quantum yield
electrons
excitation
Biological membranes
life (durability)
Lipid bilayers
Argon
Photolysis
Toluene

Keywords

  • Carotenoids
  • Electron transfer
  • Fluorescence spectroscopy
  • Porphyrins
  • Time-resolved spectroscopy

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Artificial photosynthetic reaction centers : Mimicking sequential electron and triplet-energy transfer. / Palacios, Rodrigo E.; Kodis, Gerdenis; Gould, Stephanie L.; De La Garza, Linda; Brune, Alicia; Gust, John Devens; Moore, Thomas A; Moore, Ana L.

In: ChemPhysChem, Vol. 6, No. 11, 11.11.2005, p. 2359-2370.

Research output: Contribution to journalArticle

Palacios, Rodrigo E. ; Kodis, Gerdenis ; Gould, Stephanie L. ; De La Garza, Linda ; Brune, Alicia ; Gust, John Devens ; Moore, Thomas A ; Moore, Ana L. / Artificial photosynthetic reaction centers : Mimicking sequential electron and triplet-energy transfer. In: ChemPhysChem. 2005 ; Vol. 6, No. 11. pp. 2359-2370.
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