A Single Pulse Picosecond Laser Study of Exciton Dynamics in Chloroplasts

Abstract

Abstract. Using single picosecond laser pulses at 610 nm, the fluorescence yield (φ) of spinach chloroplasts as a function of intensity (I) (1012‐1016 photons/pulse/cm2) was studied in the range of 21–300 K. The quantum yield decreases with increasing intensity and the φ vs I curves are identical at the emission maxima of 685 and 735 nm. This result is interpreted in terms of singlet exciton‐exciton annihilation on the level of the light‐harvesting pigments which occurs before energy is transferred to the Photosystem I pigments which emit at 735 nm. The yield φ is decreased by factors of 12 and 43 at 300 and 21 K, respectively. The shapes of the φ vs I curves are not well accounted for in terms of a model which is based on a Poisson distribution of photon hits in separate photosynthetic units, but can be satisfactorily described using a one‐parameter fit and an exciton‐exciton annihilation model. The bimolecular annihilation rate constant is found to be γ= (5–15) times 10‐9cm3s‐1 and to exhibit only a minor temperature dependence. Lower bound values of the singlet exciton diffusion coefficient (≥ 10‐3cm2s‐1), diffusion length (≥ 2 times 10‐6cm) and Förster energy transfer rates (≥ 3 ≥ 1010s‐1) are estimated from γ using the appropriate theoretical relationships.

Fluorescence and Photosynthesis: Gated Detection and Analysis of Nanosecond Pulse Excitation

“…Moreover, it required about 10"^ saturating laser pulses to decrease oxygen evolution by a factor of two. Thus, under the experimental conditions used in this work (1-10 pulses) the near-UV wavelength of the nitrogen laser was not changing the Chlorella, This result agrees with the known effects of UV on green algae (Halldal and Taube, 1972). However, the blue-green alga Phormidium luridum was rapidly inactivated at this wavelength.…”

“…The data include experiments with preillumination to decrease Δ, the use of Chlorella containing differing amounts of chlorophyll, and also the use of a yellow "greening" mutant of Chlorella. (Herron and Mauzerail, 1972). reaction of singlet-state chlorophyll since the latter lives only 0.3 nsec.…”

Photoelectric study on the kinetics of trapping and charge stabilization in oriented PS II membranes

“…For the energies and duration of the excitation pulses used in this study only singletsinglet annihilation is expected (Geacintov and Breton 1987). The global analysis (Table 3) (Swenberg et al 1976, Geacintov et al 1977, Deprez 1986). …”

Laser Spectroscopy of Model Photosynthetic Systems

“…resulting in a drop in 31 and T of fluorescence. Using the known excitation energy dependence of T (Geacintov et a/., 1977). one may estimate the value of y and then the value of the electronic excitation diffusion coefficient ( D ) , which is related to y (Rubin et nl., 1980).…”