Person:

Kramer, Tobias

The prevalence of long-lasting oscillatory signals in two-dimensional (2D) echo spectroscopy of light-harvesting complexes has led to a search for possible mechanisms. We investigate how two causes of oscillatory signals are intertwined: (i) electronic coherences supporting delocalized wavelike motion and (ii) narrow bands in the vibronic spectral density. To disentangle the vibronic and electronic contributions, we introduce a time-windowed Fourier transform of the signal amplitude. We find that 2D spectra can be dominated by excitations of pathways which are absent in excitonic energy transport. This leads to an underestimation of the lifetime of electronic coherences by 2D spectra.

Advances in time resolved spectroscopy have provided new insight into the energy transmission in natural photosynthetic complexes. Novel theoretical tools and models are being developed in order to explain the experimental results. We provide a model calculation for the two-dimensional electronic spectra of Cholorobaculum tepidum which correctly describes the main features and transfer time scales found in recent experiments. From our calculation one can infer the coupling of the antenna chlorosome with the environment and the coupling between the chlorosome and the Fenna-Matthews-Olson complex. We show that environment assisted transport between the subunits is the required mechanism to reproduce the experimental two-dimensional electronic spectra.