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Photo voltaic action spectra and efficiencies of chlorophyll a species absorbing near 700 nanometers

, : Photo voltaic action spectra and efficiencies of chlorophyll a species absorbing near 700 nanometers. Photochemistry & Photobiology 31(2): 143-156

Alcohol vapors affect the photovoltaic properties of anhydrous chlorophyll a (Chl a). At C, a photovoltaic cell of the type Al anhydrous Chl a Ag was successively submitted to nonsaturating vapors of methanol, ethanol, 1-propanol, 2-propanol, cyclopropyl carbinol, cyclopentanol, methyl cyclopropyl carbinol, 1-butanol, 1-pentanol and chloroethanol. The action spectrum of anhydrous Chl a has a maximum in the red at 672 nm. This maximum is shifted towards 700 nm under the influence of alcohol vapors. The most important changes occur for ethanol, 1-propanol and 2-propanol. In the same way, the conversion efficiencies of light energy into electrical energy, measured at the maximum in the red are, for the same alcohols, higher than the initial value 1.7 .times. 10-2% obtained on the average for anhydrous Chl a. A maximum value of 6.3 .times. 10-2% has been obtained after rehydration of Chl a solvated with 2-propanol. The influence of alcohol vapors has been interpreted in terms of microcapillarity of anhydrous Chl a and a mean microcavity radius of 11 .+-. 6 .ANG. was deduced from the photocurrent variation with the amount of alcohol vapor present in the measuring area. Furthermore, the action spectrum shift towards 700 nm was interpreted by the formation, at C, of Chl a special aggregates whose action spectrum was obtained by difference. IR spectroscopy demonstrated that anhydrous Chl a obtained from electrodeposition is an assembly of Chl a dimers and that alcohol vapors, producing the special aggregates formation at C, induce a decrease of the free C.dbd.O ketone band and an increase of the associated C.dbd.O esters band is not affected by the Chl a reorganization.

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