Exciton-vibrational relaxation and transient absorption dynamics in LH1 of Rhodopseudomonas viridis:: A Redfield theory approach

We explain the ultrafast transient absorption (TA) dynamics in the core LH1 antenna of Rhodopseudomonas viridis at 77 K (Monshouwer, R. Baltuska. A.: van Mourik, F.; van Grondelle, R. J, Phys. Chem. A 1998, 102, 4360) using a disordered exciton model with strong coupling to two vibrational modes and weak coupling of vibrational and electronic coordinates to the thermal bath. A quantitative fit of the excitation wavelength-dependent TA dynamics was obtained using the density matrix equation with the Redfield relaxation operator. The sequential and coherent contributions to the TA dynamics were analyzed separately. The time-dependent red shift of TA was explained in terms of exciton relaxation. The lifetimes of higher exciton states of 12-75 fs (depending on the state) were determined from the fit.