Picosecond fluorescence studies of photosystem II.

Much effort has been expended in the measurement of the fluorescence decay kinetics of chlorophyll in vioo (for examples see papers cited in Harris et al., 1976). To the present time most techniques have lacked either the precision or the time resolution required for accurate determinations. Recent work using high-powered lasers has been hampered asa result of anomalousmultiphotoneffects(Campillo et al., 19766; Porter eta!., 1977). In the present paper we report measurements of Photosystem I1 fluorescence using a single-photon counting technique utilizing low-power excitation from a tunable dye laser. This method has the advantages of a much better time-resolution capability than conventional single-photon counting techniques (Wild et a/., 1977; Spears et al., 1978) and of a higher sensitivity, enabling much lower incident light intensities to be used than those required for streak-camera or fast-shutter methods.