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Fluorescence anisotropy of chlorophyll a and chlorophyll b in castor oil

1989; Elsevier BV; Volume: 973; Issue: 3 Linguagem: Inglês

10.1016/s0005-2728(89)80382-2

1879-2650

M. van Gurp, G. van Ginkel, Y.K. Levine,

Spectroscopy and Quantum Chemical Studies

A detailed study of the fluorescence anisotropy of chlorophyll a and chlorophyll b in castor oil is presented. Scanningacross the wavelength of emission the value of the fluorescence anisotropy shows a considerable variation. This indicates that differently polarized emission moments are present. When excitation spectra of the fluorescence anisotropy are recorded at two distinct emission wavelengths, two separate curves are foundthat cross each other several times. The difference between the two spectra yields information about the extent to which absorption transitions overlap. It is found that over the whole spectrum of visible light, absorption transition bands overlap, so that the valueof the fluorescence anisotropy cannot be interpreted in terms of a single anglebetween absorption and emission moment. It rather yields an average direction of the overlapping transitions. Castor oil at room temperature is not sufficiently viscous to quench the rotational depolarization of the chlorophyll fluorescence. A limiting valueof the fluorescence anisotropy is obtained using time-resolved measurements.