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The selective picosecond excitation of Rhodopseudomonas sphaeroides (R-26) reaction centers (RCs) at 870 nm induces the formation of the transient state within < 1 ps followed by the conversion into the state PF (P'+Bph'-) during 7 it 2 ps at both 293 K and 110 K. The transient state including the intense bleaching at 8OOnm has been shown not to be due: (a) to photon excitation at 870nm; (b) the excitation of P+; (c) photoselection effects. The transient state is interpreted as the state '[P+B-] in agreement with earlier works. The primary formation of the state '[P+B-] and the big effective singlet-triplet splitting in this state correspond to the spectral splitting of the P band at 900nm in R-26 RCs and at 1000 nm in Rhodopseudomonas viridis RCs found at 4.2K and attributed to the optical transition to both 'P and '[P+B-] states. Selective picosecond spectroscopy Bacterial reaction center Electron transfer bacteriochiorophyll

Burning of spectral holes within the absorption band of the primary electron donor P in reaction centers of Rhodopseudomenus viridis is studied using selective excitation at 1014 nm and 1.7 K. A narrow (< I .O cm-') spectral hole with relatively weak electron-phonon and vibronic coupling is burned if the intermediary electron acceptor I is pre-reduced. The hole is broadened up to -9&150 cm-i if I is neutral and the electron-transfer chain is open. Broadening of the hole is discussed in terms of the fast (_ 7&l 10 fs) electron hopping between P* and P+BL-(BL, bacteriochlorophyll monomer in L protein subunit).