Conformationally constrained macrocyclic diporphyrin-fullerene artificial photosynthetic reaction center

Vikas Garg, Gerdenis Kodis, Mirianas Chachisvilis, Michael Hambourger, Ana L Moore, Thomas A Moore, John Devens Gust

Research output: Contribution to journalArticle

62 Citations (Scopus)

Abstract

Photosynthetic reaction centers convert excitation energy from absorbed sunlight into chemical potential energy in the form of a charge-separated state. The rates of the electron transfer reactions necessary to achieve long-lived, high-energy charge-separated states with high quantum yields are determined in part by precise control of the electronic coupling among the chromophores, donors, and acceptors and of the reaction energetics. Successful artificial photosynthetic reaction centers for solar energy conversion have similar requirements. Control of electronic coupling in particular necessitates chemical linkages between active component moieties that both mediate coupling and restrict conformational mobility so that only spatial arrangements that promote favorable coupling are populated. Toward this end, we report the synthesis, structure, and photochemical properties of an artificial reaction center containing two porphyrin electron donor moieties and a fullerene electron acceptor in a macrocyclic arrangement involving a ring of 42 atoms. The two porphyrins are closely spaced, in an arrangement reminiscent of that of the special pair in bacterial reaction centers. The molecule is produced by an unusual cyclization reaction that yields mainly a product with C2 symmetry and trans-2 disubstitution at the fullerene. The macrocycle maintains a rigid, highly constrained structure that was determined by UV-vis spectroscopy, NMR, mass spectrometry, and molecular modeling at the semiempirical PM6 and DFT (B3LYP/6-31G) levels. Transient absorption results for the macrocycle in 2-methyltetrahydrofuran reveal photoinduced electron transfer from the porphyrin first excited singlet state to the fullerene to form a P•+- C60•--P charge separated state with a time constant of 1.1 ps. Photoinduced electron transfer to the fullerene excited singlet state to form the same charge-separated state has a time constant of 15 ps. The charge-separated state is formed with a quantum yield of essentially unity and has a lifetime of 2.7 ns. The ultrafast charge separation coupled with charge recombination that is over 2000 times slower is consistent with a very rigid molecular structure having a small reorganization energy for electron transfer, relative to related porphyrin-fullerene molecules.

Original languageEnglish
Pages (from-to)2944-2954
Number of pages11
JournalJournal of the American Chemical Society
Volume133
Issue number9
DOIs
Publication statusPublished - Mar 9 2011

Fingerprint

Photosynthetic Reaction Center Complex Proteins
Fullerenes
Porphyrins
Electrons
Quantum yield
Excited states
Solar Energy
Molecules
Molecular modeling
Excitation energy
Sunlight
Chemical potential
Cyclization
Energy Transfer
Chromophores
Potential energy
Molecular Structure
Ultraviolet spectroscopy
Energy conversion
Discrete Fourier transforms

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Conformationally constrained macrocyclic diporphyrin-fullerene artificial photosynthetic reaction center. / Garg, Vikas; Kodis, Gerdenis; Chachisvilis, Mirianas; Hambourger, Michael; Moore, Ana L; Moore, Thomas A; Gust, John Devens.

In: Journal of the American Chemical Society, Vol. 133, No. 9, 09.03.2011, p. 2944-2954.

Research output: Contribution to journalArticle

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