Femtosecond vibrational dynamics and relaxation in the core light-harvesting complex of photosynthetic purple bacteria

Using 50 fs light pulses we have observed the wavelength dependent phase shifts of oscillatory transients in the transient absorption kinetics of the LH1 complex from purple bacteria at 77 K. We applied the density operator formalism in Liouville space in combination with Redfield relaxation theory to calculate the transient absorption response of the model system consisting of three electronic states and one vibrational mode linearly coupled to the thermal bath. This enabled us to estimate relative displacements of the potential energy surfaces in the higher excited states of the LH1 complex and investigate the influence of coherence transfer processes.