Nature of the ground and first excited states of the radical cations of photosynthetic bacterial reaction centres Original Research Article

The band shapes of the ∼ 2500 cm−1 electronic absorption (intervalence) transition in radical cations of the photosynthetic reaction centres of Rhodobacter sphaeroides and Rhodopseudomonas viridis are analysed to extract electronic couplings, asymmetries, and reorganization energies. According to this standard analysis, the charge is highly localized on one bacteriochlorophyll of the special pair, in accord with interpretations of older resonance Raman data but in contrast to interpretations of recent ENDOR and TRIPLE data; however, our conclusions are not beyond doubt and the need for further experimental work is indicated. The significance of the observed phase-phonon lines is also discussed, as are some possible consequences of the nature of P+ for the overall kinetics of the reaction centre.