Efficient energy transfer and electron transfer in an artificial photosynthetic antenna-reaction center complex

Gerdenis Kodis, Paul A. Liddell, Linda De la Garza, P. Christian Clausen, Jonathan S. Lindsey, Ana L Moore, Thomas A Moore, John Devens Gust

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Abstract

A highly efficient functional mimic of a photosynthetic antenna-reaction center complex has been designed, synthesized, and studied spectroscopically. The antenna, consisting of four covalently linked zinc tetraarylporphyrins, (PZP)3-PZC, has been coupled to a free-base porphyrin-fullerene artificial photosynthetic reaction center, P-C60, to form a (PZP)3-PZC-P-C60 hexad. As revealed by time-resolved absorption and emission studies in 2-methyltetrahydrofuran solution at ambient temperature, excitation of a peripheral zinc porphyrin moiety is followed by singlet-singlet energy transfer to the central zinc porphyrin to give (PZP)3-1PZC-P-C60 with a time constant of 50 ps. The excitation is passed on to the free-base porphyrin in 32 ps to produce (PZP)3-PZC-1P-C60, which decays by electron transfer to the fullerene with a time constant of 25 ps. The resulting (PZP)3-PZC-P.+-C60.- charge-separated state is generated with a quantum yield of 0.98 based on light absorbed by the porphyrin antenna. Direct excitation of the free-base porphyrin moiety or the fullerene also generates this state with a yield near unity. Thermodynamically favorable migration of positive charge into the zinc porphyrin array transforms the initial state into a long-lived ((PZP)3-PZC).+-P-C60 .- charge-separated state with a time constant of 380 ps. The final charge-separated state, formed in high yield (∼0.90), decays to the ground state with a lifetime of 240 ns. In benzonitrile, the lifetime is 25 μs. A previous hexad, which differs from the current hexad solely in the nature of the free-base porphyrin, gave a charge-separated state with a lower yield (0.69) and a shorter lifetime (1.3 ns). The difference in performance is attributed to differences in electronic composition (a2u versus a1u HOMO), conformation, and oxidation potential (1.05 versus 0.84 V) between the meso-tetraarylporphyrin and the β-octaalkylporphyrin of the current and former hexads, respectively. These results can be explained on the basis of an understanding of factors that affect through-bond energy-transfer and electron-transfer processes. The results demonstrate that it is possible to design and prepare synthetic, porphyrin-based antenna-reaction center complexes that mimic the basic photochemical functions of natural photosynthetic light-harvesting antennas and reaction centers in simple, structurally well-defined constructs.

Original languageEnglish
Pages (from-to)2036-2048
Number of pages13
JournalJournal of Physical Chemistry A
Volume106
Issue number10
DOIs
Publication statusPublished - Mar 14 2002

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Porphyrins
porphyrins
Energy transfer
electron transfer
antennas
energy transfer
Antennas
Fullerenes
Electrons
zinc
time constant
fullerenes
Photosynthetic Reaction Center Complex Proteins
life (durability)
Quantum yield
Ground state
excitation
Conformations
Zinc
decay

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Efficient energy transfer and electron transfer in an artificial photosynthetic antenna-reaction center complex. / Kodis, Gerdenis; Liddell, Paul A.; De la Garza, Linda; Clausen, P. Christian; Lindsey, Jonathan S.; Moore, Ana L; Moore, Thomas A; Gust, John Devens.

In: Journal of Physical Chemistry A, Vol. 106, No. 10, 14.03.2002, p. 2036-2048.

Research output: Contribution to journalArticle

Kodis, Gerdenis ; Liddell, Paul A. ; De la Garza, Linda ; Clausen, P. Christian ; Lindsey, Jonathan S. ; Moore, Ana L ; Moore, Thomas A ; Gust, John Devens. / Efficient energy transfer and electron transfer in an artificial photosynthetic antenna-reaction center complex. In: Journal of Physical Chemistry A. 2002 ; Vol. 106, No. 10. pp. 2036-2048.
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N2 - A highly efficient functional mimic of a photosynthetic antenna-reaction center complex has been designed, synthesized, and studied spectroscopically. The antenna, consisting of four covalently linked zinc tetraarylporphyrins, (PZP)3-PZC, has been coupled to a free-base porphyrin-fullerene artificial photosynthetic reaction center, P-C60, to form a (PZP)3-PZC-P-C60 hexad. As revealed by time-resolved absorption and emission studies in 2-methyltetrahydrofuran solution at ambient temperature, excitation of a peripheral zinc porphyrin moiety is followed by singlet-singlet energy transfer to the central zinc porphyrin to give (PZP)3-1PZC-P-C60 with a time constant of 50 ps. The excitation is passed on to the free-base porphyrin in 32 ps to produce (PZP)3-PZC-1P-C60, which decays by electron transfer to the fullerene with a time constant of 25 ps. The resulting (PZP)3-PZC-P.+-C60.- charge-separated state is generated with a quantum yield of 0.98 based on light absorbed by the porphyrin antenna. Direct excitation of the free-base porphyrin moiety or the fullerene also generates this state with a yield near unity. Thermodynamically favorable migration of positive charge into the zinc porphyrin array transforms the initial state into a long-lived ((PZP)3-PZC).+-P-C60 .- charge-separated state with a time constant of 380 ps. The final charge-separated state, formed in high yield (∼0.90), decays to the ground state with a lifetime of 240 ns. In benzonitrile, the lifetime is 25 μs. A previous hexad, which differs from the current hexad solely in the nature of the free-base porphyrin, gave a charge-separated state with a lower yield (0.69) and a shorter lifetime (1.3 ns). The difference in performance is attributed to differences in electronic composition (a2u versus a1u HOMO), conformation, and oxidation potential (1.05 versus 0.84 V) between the meso-tetraarylporphyrin and the β-octaalkylporphyrin of the current and former hexads, respectively. These results can be explained on the basis of an understanding of factors that affect through-bond energy-transfer and electron-transfer processes. The results demonstrate that it is possible to design and prepare synthetic, porphyrin-based antenna-reaction center complexes that mimic the basic photochemical functions of natural photosynthetic light-harvesting antennas and reaction centers in simple, structurally well-defined constructs.

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