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FREE ENERGY DEPENDENCE OF THE QUENCHING OF CHLOROPHYLL a FLUORESCENCE BY SUBSTITUTED QUINONES *
Author(s) -
Natarajan L. V.,
Blankenship R. E.
Publication year - 1983
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1983.tb04481.x
Subject(s) - quenching (fluorescence) , chemistry , photochemistry , electron transfer , excited state , fluorescence , acetonitrile , marcus theory , analytical chemistry (journal) , reaction rate constant , kinetics , atomic physics , organic chemistry , physics , quantum mechanics
The quenching of chlorophyll a (Chl a ) fluorescence hy a series of substituted benzoquinones. naphthoquinones and anthraquinones has been examined employing ethanol and acetonitrile as solvents. All quinones are good quenchers of fluorescence. There is an excellent linear relation between the Stern‐Volmer quenching constants, K , and the polarographic half wave potentials ( E 1 2 ) of the quinones, with more oxidizing quinones being better quenchers. The quenching data are consistent with the excited state half wave potential of −1.31 eV predicted theoretically, demonstrating that the kinetically estimated value of the Chl a excited state reduction potential agrees with that expected on spectroscopic grounds. The results of quenching are not in agreement with the conventional Marcus theory of electron‐transfer reactions, as there is no evidence of quenching constant. K q . decrease vs Δ G 0 even for free energy changes nearly twice that expected for the onset of the Marcus inverted region. However, the kinetically estimated K q values are in good agreement with the ones calculated by using the Rehm and Weller equation for fluorescence quenching by electron transfer. Our experimental results support the electron transfer mechanism of quenching proposed by Seely.