Two-excitons, annihilation and coherent multidimensional spectroscopy:
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| Tõnu Pullerits | |
| Lund University | |
| Exciton-exciton annihilation occurs when two excitations are simultaneously generated within a so called domain - interconnected part of a light harvesting antenna. If two excitations come into close proximity, they may fuse forming a doubly excited state. From this state fast internal conversion to the first excited state follows reducing the number of excitations. Annihilation conditions are easy to create by pulsed laser excitation and it can be utilized to study size, connectivity, electronic structure and dynamics of photosynthetic antenna systems [1, 2]. Besides acting as tool, the annihilation can also lead to unwanted experimental errors. We showed recently that the annihilation-related fifth order terms may interfere with the common third order terms in coherent multidimensional spectroscopy experiments [3]. The effect can substantially distort the results since excitation intensities in such experiments are usually quite high. We have also studied temperature dependence of the excitation annihilation in the peripheral light harvesting antenna (LH2) of photosynthetic purple bacterium Rhodobacter (Rb.) sphaeroides [4]. Multi-exciton density matrix formalism was used to describe the experimental kinetics. We could draw conclusions about temperature dependence of the intramolecular internal conversion rate in bacteriochlorophyll (BChl) molecules. The same formalism was used to calculate various fifth order coherent multidimensional signals [5]. 1. G. Trinkunas, J.L. Herek, T. Polivka, V. Sundström, T. Pullerits. 2001. Exciton delocalization probed by excitation annihilation in the light-harvesting antenna LH2. Phys. Rev. Lett. 86: 4167-4170. 2. A. Schubert, A. Stenstam, W. J. D. Beenken, J. L. Herek, R. J. Cogdell, T. Pullerits and V. Sundström. 2004. Self-assembly of the bacterial LH2 revealed by ultrafast spectroscopy and electron microscopy. Biophys. J. 86:2363-2373. 3.B. Brüggemann, P. Kjellberg and T. Pullerits. 2007. Non-perturbative calculation of 2D spectra in heterogeneous systems: Exciton relaxation in the FMO complex. Chem. Phys. Lett. 444: 192-196. 4. B. Brüggemann, N. Christensson and T. Pullerits. 2009. Temperature dependent exciton-exciton annihilation in the LH2 antenna complex. Chem. Phys.357:140-143. 5. B. Brüggemann and T. Pullerits. 2011. Nonperturbative modeling of fifth-order coherent multidimensional spectroscopy in light harvesting antennas. New J. Phys. 13:025024 |