Holzapfel, Wolfgang; Finkele, Ulrich; Kaiser, Wolfgang; Oesterhelt, Dieter; Scheer, Hugo; Stilz, Hans Ulrich; Zinth, Wolfgang
Observation of a bacteriochlorophyll anion radical during the primary charge separation in a reaction center.
In: Chemical Physics Letters, Vol. 160, No. 1: pp. 1-7
The primary light-induced charge separation in reaction centers of Rhodobacter sphaeroides was investigated with femtosecond time resolution. The absorption changes in the time range 100 fs to 1 ns observed after direct excitation of the primary donor P at 860 nm could only be explained by a kinetic model which uses three time constants. This finding supports the following reaction scheme: (i) the electronically excited primary donor P* decays with a time constant of 3.5 ps and populates a very short-lived intermediate involving a reduced accessory bacteriochlorophyll molecule; (ii) with a time constant of 0.9 ps the electron is transferred to the neighboring bacteriopheophytin molecule; and (iii) from there within 200 ps to the quinone.