Excitation energy transfer pathways in asymmetric covalent chlorophyll a tetramers

Victoria L. Gunderson, Thea M. Wilson, Michael R Wasielewski

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

We report the observation of multiple excitation energy transfer (EET) pathways in a covalently linked, chlorophyll (Chl) tetramer having three different fixed Chl-Chl distances. The tetramer was synthesized by covalently attaching 20-(4-ethynylphenyl)Chl to the 1,3,6,8-positions of pyrene to give Chl 4-py. Reference Chl oligomers were prepared by attaching 20-(4-ethynylphenyl)Chl to the 1-position of pyrene (Chl-py), the 1,8 and 3,6 positions of pyrene (para-Chl2-py and ortho-Chl2-py, respectively), and the 1,3,5-positions of benzene (meta-Chl3). The Chlx-py derivatives were studied using femtosecond transient absorption (TA) and transient absorption anisotropy (TAA) spectroscopy, and compared with data obtained earlier on meta-Chl3. Using femtosecond TA, the decay of Chl 4-py was monitored after photoexcitation of its Q y band with a 655 nm, 130 fs laser pulse. A triexponential decay of 1*Chl 4-py (τ = 7 ps, 152 ps, and 4.2 ns) was observed, with the two shorter time constants being laser intensity dependent. This dependency is indicative of singlet- singlet annihilation and is attributed to EET via two pathways, those involving the two closest Chl's (ortho/meta), which are kinetically indistinguishable, and the two most distant (para) Chl's. Further confirmation of multiple EET pathways was made by femtosecond TAA measurements. Forster energy transfer lifetimes were calculated for the three possible energy transfer pathways (ortho,20ps; meta, 34 ps; and para, 150 ps) and compared to the experimental results. Our results indicate that EET between nonadjacent chromophores having high oscillator strengths, such as the para Chl's in Chl 4-py, is significant, and the additional utilization of the minor EET contributing pathways may provide greater avenues for designing efficient light harvesting in future artificial photosynthetic systems.

Original languageEnglish
Pages (from-to)11936-11942
Number of pages7
JournalJournal of Physical Chemistry C
Volume113
Issue number27
DOIs
Publication statusPublished - Jul 9 2009

Fingerprint

Excitation energy
chlorophylls
Chlorophyll
Energy transfer
energy transfer
excitation
Pyrene
pyrenes
Anisotropy
chlorophyll a
anisotropy
Photoexcitation
decay
Chromophores
Benzene
photoexcitation
oligomers
Oligomers
oscillator strengths
chromophores

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

Excitation energy transfer pathways in asymmetric covalent chlorophyll a tetramers. / Gunderson, Victoria L.; Wilson, Thea M.; Wasielewski, Michael R.

In: Journal of Physical Chemistry C, Vol. 113, No. 27, 09.07.2009, p. 11936-11942.

Research output: Contribution to journalArticle

Gunderson, Victoria L. ; Wilson, Thea M. ; Wasielewski, Michael R. / Excitation energy transfer pathways in asymmetric covalent chlorophyll a tetramers. In: Journal of Physical Chemistry C. 2009 ; Vol. 113, No. 27. pp. 11936-11942.
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