Controlling Ultrafast Processes in Biological Chromophores with Femtosecond Lasers

Tiago Buckup, Jürgen Hauer, and Marcus Motzkus

Faculty of Chemistry, University of Marburg, Hans-Meerwein-Straße, 35032 Marburg, Germany




The goal of quantum control with femtosecond lasers is to adapt the spectral and temporal characteristics of the excitation light to the inherent molecular resonances and dynamics, in such a way, that ultrafast molecular processes can be not just selectively addressed but also manipulated. This is especially attractive in the case of complex systems like biological chromophores, due to the possible insight gain on light-steered functions and potential technological applications.

Carotenoids are biological molecules with an important role in the light harvesting processes of bacteria and plants. Quantum control, as a new spectroscopy tool, is able to investigate the ultrafast molecular dynamics of carotenoids and clarify its complex electronic network. In our group, several carotenoids with different conjugation lengths were systematically studied in solution as well as embedded in the bacterial light-harvesting antenna complex (LH2) of R. acidophila, a photosynthetic purple bacterium.

Carotenoids in their biological function show usually a complex energy deactivation network with overlapping absorption bands. This demands a new spectroscopy method. Quantum control spectroscopy offers here a way out of this problem: with adapted laser pulses it is possible to choose a particular energy pathway and, thus, allowing the separation of specific electronic states. Quantum control was combined with several time-resolved nonlinear techniques, as transient absorption and degenerate four-wave-mixing, with resolutions better than 20 fs and was applied to several biological examples.