PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

Resolving the excited state equilibrium of peridinin in solution. Emmanouil Papagiannakis^*,1, Delmar Larsen¹, Ivo van Stokkum¹, Mikas Vengris¹, Roger Hiller², Rienk van Grondelle¹, ¹ Department of Physics and Astronomy, Faculty of Sciences, Amsterdam, The Netherlands² School of Biological Sciences, Sydney, New South Wales, Australia

ABSTRACT- The carotenoid peridinin is abundant in the biosphere, as it is the main pigment bound by the light-harvesting complexes of dinoflagellates, where it collects blue and green sunlight and transfers energy to chlorophyll-a with high efficiency. Its molecular structure is particularly complex, giving rise to an intricate excited-state manifold, which includes a state with intramolecular charge-transfer (ICT) characteristics. To disentangle the excited states of peridinin and understand their function in vivo we applied dispersed pump-probe and pump-dump-probe spectroscopy. The preferential depletion of population from the ICT state by the dump pulse demonstrates that the S₁ and the ICT state are distinct entities. The ensuing dump-induced dynamics illustrates the equilibration of these states which occurs on the timescale of a few picoseconds. Additionally, the dump pulse populates a short-lived ground state intermediate, which is suggestive of a complex relaxation pathway, probably including structural reorientation or solvation of the ground state. These findings indicate that the unique ICT state of peridinin is an efficient energy donor to chlorophyll a in the Peridinin-Chlorophyll-a-Protein complex and thus plays a significant role in global light-harvesting.

KEY WORDS: CAROTENOID