Transient Absorption of Chlorophylls and Carotenoids after Two-Photon Excitation of LHCII

• Published in: The journal of physical chemistry letters 2021-04, Vol.12 (12), p.3176-3181
• Main Authors: Šebelík, Václav, Kuznetsova, Valentyna, Lokstein, Heiko, Polívka, Tomáš
• Format: Article
• Language: English
• Subjects: Physical Insights into the Biosphere, Atmosphere, and Space
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.1c00122

Femtosecond transient absorption spectroscopy following two-photon excitation (2PE) is used to determine the contributions of carotenoids and chlorophylls to the 2PE signals in the main plant light-harvesting complex (LHCII). For 2PE, excitation at 1210 and 1300 nm was used, being within the known 2PE profile of LHCII. At both excitation wavelengths, the transient absorption spectra exhibit a shape characteristic of excited chlorophylls with only a minor contribution from carotenoids. We compare the 2PE data measured for LHCII with those obtained from 2PE of a lutein/chlorophyll a mixture in acetone. We estimate that although the 2PE cross section of a single carotenoid in acetone is ∼1.7 times larger than that of a Chl a, due to the 1:3.5 carotenoid/Chl ratio in LHCII, only one-third of the absorbed 2PE photons excite carotenoids in LHCII in the 1200–1300 nm range.