Chlorophyll Triplet States in the CP47-D1-D2-Cytochrome b-559 Complex of Photosystem II

Chlorophyll triplet states have been induced at cryogenic temperatures by illumination of isolated photosystem II CP47-Dl-D2-Cytochrome b-559 (CP47-RC) and D1-D2-Cytochrome b-559 (RC) complexes with repetitive laser flashes. The triplet induced in RC and RC-CP47 complexes had a lifetime of 1.6 ms (at 77K) and was characterized by an absorbance difference spectrum peaking at 680 nm. In CP47-RC complexes, an antenna triplet on CP47 was found with a lifetime of 0.7 ms; the quantum yield of radical pair triplet formation was about 0.2–0.3 below 100K and decreased at higher temperatures. The temperature dependence was analyzed with an equilibrium model for the chlorophyll excited states and the radical pair; the free energy change (ΔG) for charge separation was found to be about -50 meV and independent of temperature.