Electrochemical production of chlorophyll a and pheophytin a excited states

Michael R. Wasielewski, Rebecca L. Smith, Arthur G. Kostka

Research output: Contribution to journalArticle

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Abstract

The reaction of chlorophyll a+ (Chl a+) with either Chl a- or pheophytin a- (Pheo a-) in addition to the reaction of Pheo a+ with Pheo a- was studied in butyronitrile (BCN), BCN-1% THF, THF, and DMF. The electrochemically produced radical ion pairs Chl a+-Chl a- and Pheo a+-Pheo a- react in each solvent to produce a 10-7-10-6 yield of luminescent states on the basis of the initial number of radical pairs. The Chl a+-Pheo a- reaction produces no observable luminescence in any of the solvents examined. The luminescence maximum for the Pheo a+-Pheo a- reaction occurs at 730 nm in each solvent and is strongly red-shifted relative to the fluorescence maxima for optically excited Pheo a in these solvents. A similar result is obtained for the Chl a+-Chl a- reaction in BCN. However, emission from the Chl a+-Chl a- reaction in the other three solvents occurs at 680 nm and corresponds more closely to normal fluorescence from optically excited Chl a. The red-shifted spectra are consistent with the formation of excimers. AC voltammetry of Chl a in BCN provides evidence that Chl a is aggregated in the ground state in this solvent. Chl a reduction shows four waves in BCN and two waves in the other three solvents. Thus, the Chl a+-Chl a- reaction in BCN does not form a true excimer, whereas the Pheo a+-Pheo a- reactions in each solvent do. The luminescence efficiencies of these charge-transfer neutralization reactions are discussed in terms of the geometric constraints on electron-transfer reactions in photosynthetic reaction centers.

Original languageEnglish
Pages (from-to)6923-6928
Number of pages6
JournalJournal of the American Chemical Society
Volume102
Issue number23
Publication statusPublished - 1980

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Chlorophyll
Excited states
Luminescence
Fluorescence
Photosynthetic Reaction Center Complex Proteins
pheophytin a
chlorophyll a
Voltammetry
Ground state
Charge transfer
Electrons
Ions

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Electrochemical production of chlorophyll a and pheophytin a excited states. / Wasielewski, Michael R.; Smith, Rebecca L.; Kostka, Arthur G.

In: Journal of the American Chemical Society, Vol. 102, No. 23, 1980, p. 6923-6928.

Research output: Contribution to journalArticle

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