Temperature dependent exciton-exciton annihilation in the LH2 antenna complex

Two-color pump-probe measurements of the peripheral light harvesting complex LH2 of Rb.sphaeroides reveal strong temperature dependence of the annihilation rate. The experimental results were modeled via multi-exciton density matrix theory. Based on available literature data we can set an upper limit for the feasible intramolecular internal conversion rate. We show that this also restricts the possible values of the still ill-determined energy of the doubly-excited molecular level of the bacteriochlorophyll, which is responsible for the annihilation process.