Excited-state dynamics of protochlorophyllide revealed by subpicosecond infrared spectroscopy |
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Authors: | Colindres-Rojas Miriam Wolf Matthias M N Gross Ruth Seidel Sonja Dietzek Benjamin Schmitt Michael Popp Jürgen Hermann Gudrun Diller Rolf |
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Affiliation: | †Department of Physics, Technical University Kaiserslautern, Kaiserslautern, Germany;‡Institute of Biochemistry and Biophysics, Friedrich Schiller University Jena, Jena, Germany;§Institute of Physical Chemistry, Friedrich Schiller University Jena, Jena, Germany;¶Institute of Photonic Technology Jena, Jena, Germany |
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Abstract: | To gain a better understanding of the light-induced reduction of protochlorophyllide (PChlide) to chlorophyllide as a key regulatory step in chlorophyll synthesis, we performed transient infrared absorption measurements on PChlide in d4-methanol. Excitation in the Q-band at 630 nm initiates dynamics characterized by three time constants: τ1 = 3.6 ± 0.2, τ2 = 38 ± 2, and τ3 = 215 ± 8 ps. As indicated by the C13′=O carbonyl stretching mode in the electronic ground state at 1686 cm−1, showing partial ground-state recovery, and in the excited electronic state at 1625 cm−1, showing excited-state decay, τ2 describes the formation of a state with a strong change in electronic structure, and τ3 represents the partial recovery of the PChlide electronic ground state. Furthermore, τ1 corresponds with vibrational energy relaxation. The observed kinetics strongly suggest a branched reaction scheme with a branching ratio of 0.5 for the path leading to the PChlide ground state on the 200 ps timescale and the path leading to a long-lived state (>>700 ps). The results clearly support a branched reaction scheme, as proposed previously, featuring the formation of an intramolecular charge transfer state with ∼25 ps, its decay into the PChlide ground state with 200 ps, and a parallel reaction path to the long-lived PChlide triplet state. |
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