Dephasing Times in the Phycobiliprotein Antenna Complexes PE545 and PE555

Abstract

Since long-lived quantum coherence have not only been observed in the Fenna-Matthews-Olson (FMO) complex of green sulfur bacteria but also in the phycoerythrin 545 (PE545) photosynthetic antenna system, the interest in these systems has been increased significantly. Moreover, similar results have been found for the PE555 complex in which the two alpha-beta monomers are rotated compared to the PE545 structure leading to a water filled channel. By now, all three complexes have been investigated by a sequential combination of molecular dynamics (MD) simulations, calculations of vertical excitation energies along the trajectory and quantum dynamics for the exciton transfer [1-3]. A comparison of the obtained spectral densities and dynamics will be provided. An interesting property for the systems is the dephasing time which can give an estimate for how long quantum coherences might survive in the respective system. In a first step, the relationship between dephasing time and energy gap fluctuations of the individual pigments has been determined [4]. For the above mentioned complex but also additional exciton and charge transfer systems it can be confirmed that that an inverse proportionality exists between dephasing time and average gap energy fluctuation. Interestingly, an interestingly very similar behavior has been found for all these systems. In a subsequent step, the relationship between dephasing time and excitonic energy gap fluctuations for entire complexes including the respective inter-molecular couplings has been studied.[1] C. Olbrich, J. Strumpfer, K. Schulten, U. Kleinekathofer, J. Phys. Chem. Lett. 2, 1771 (2011).[2] M. Aghtar, J. Strumpfer, C. Olbrich, K. Schulten, U. Kleinekathofer, J. Phys. Chem. Lett. 5, 3131 (2014).[3] S. Chandrasekaran, K. R. Pothula, U. Kleinekathofer, J. Phys. Chem. B, DOI: 10.1021/acs.jpcb.6b05803 (2016).[4] M. I. Mallus, M. Aghtar, S. Chandrasekaran, G. Ludemann, M. Elstner, U. Kleinekathofer, J. Phys. Chem. Lett. 7, 1102 (2016).