Primary Charge Separation in Reaction Centers: Time-Resolved Spectral Features of Electric Field Induced Reduction of Quantum Yield

Electric field effects on reaction centers from Rb. sphaeroides have been detected in ps transient absorption at 90K. Upon application of a field of 7105V/cm the bleaching of the bacteriopheophytin at the A-branch (HA, 545nm) monitored after 30ps mirrors a reduction of the quantum yield of P+H A - formation by ⋍11% (P being the special pair). A similar field induced reduction of the quantum yield is observed when probing the bleaching of P at 870nm. However, this effect evolves with a time constant of ⋍900ps. We conclude that the loss channel employs an intermediate state with this lifetime before repopulating the ground state. Field induced formation of P+H B - (B-branch) was excluded from measurements in the Qx transition of HB at 533nm. Measurements in the blue and red wings of the 800nm Qy band of the two bac-teriochlorophylls (BA and BB) are compatible with the state P+H A - being the long-lived intermediate involved in the loss of quantum yield.