Dresden 2020 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 22: Single Molecule Biophysics (joint session BP/CPP)
BP 22.8: Vortrag
Mittwoch, 18. März 2020, 12:00–12:15, SCH A251
Q band mixing in chlorophyll a - spectral decomposition of Qx and Qy absorption bands — •Clark Zahn1, Till Stensitzki1, Angelica Zacarias2, and Karsten Heyne1 — 1Institutfür Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany — 2Max Planck Institute of Microstructure Physics, Weinberg 2, D06120 Halle, Germany and ETSF
Chlorophyll a (Chl a) is one of the most abundant pigments on earth, responsible for the green color of plants. Despite extensive research, the composition of its visible Q absorption band is yet not well understood. Here, we apply polarization resolved femtosecond Vis pump - IR probe spectroscopy, providing a detailed insight into Q band mixing of Chl a. Vis excitation was tuned to various wavelengths scanning the Q band absorption. We show that the dichroic ratio of the keto-C=O stretching vibration at 1698 cm-1 strongly depends on the excitation wavelength. Hence, the angle between the excited electronic transition dipole moment (tdm) and the vibrational keto-C=O tdm changes significantly across the Q band. Tracing the relative angle Θ for different excitation wavelengths allows to determine the Qx contribution along the Q band region. In this way, Qx is found to contribute 40-60% to absorption of the lower energetic peak at 618 nm and to 75-100% to the absorption of the high energy flank at around 580 nm. Complementary measurements on the C=C stretching vibration at 1608 cm-1 provide corroborating evidence for our findings. Further, we show that from our recent results the three-dimensional orientation of the Qx and Qy tdms can be resolved under guidance of quantum chemical calculations.