BPCPPDYSOE21 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 16: Single Molecule Biophysics II
BP 16.6: Vortrag
Dienstag, 23. März 2021, 12:40–13:00, BPa
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. Despite extensive research, the composition of its absorption spectrum 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. The excitation was tuned to various wavelengths covering 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. By tracing this angle Θ for different excitation wavelengths, we are able to determine the Qx contribution along the Q band region. We find that Qx contributes 42-71% to the absorption of the lower energetic peak at 618 nm and to 59-100% 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. Our results provide a direct spectral disentanglement of the Q band, without any previous assumptions. Thus, making them a reliable benchmark for quantum chemical calculations.