FLUORESCENCE LIFETIMES OF CHLOROPHYLL a: SOLVENT, CONCENTRATION AND OXYGEN DEPENDENCE |
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Authors: | John S ConnollyA Frederick Janzen†Edward B Samuel |
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Institution: | Photoconversion Research Branch, Solar Energy Research Institute, Golden, CO 80401, USA.;Photochemical Research Associates, 45 Meg Drive, London, Ontario N6E 2V2, Canada |
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Abstract: | Fluorescence lifetimes (τf) of chlorophyll a (Chi a ) have been measured by the single-photon-counting technique over a wide range of concentrations (?10-7?10-4 M ) in deoxygenated pyridine, diethyl ether, toluene and methanol. At pigment concentrations ?1 μ M , reabsorption of fluorescence induces significant artifacts on measured values of τf which are dependent on detection wavelength and the specific geometry of the experiment. There is a clear dependence of τf on the nature and degree of solvation, including both coordination of the central magnesium and hydrogen-bonding of the solvent (viz. alcohols) to the macrocycle. Quenching of the excited singlet state by molecular oxygen was measured quantitatively in ether, and a bimolecular rate constant markedly slower than the diffusion-controlled limit was obtained. |
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