Femtosecond visible transient absorption spectroscopy of chlorophyll--containing photosystem II.

The recently discovered, chlorophyll--containing, far-red photosystem II (FR-PSII) supports far-red light photosynthesis. Participation and kinetics of spectrally shifted far-red pigments are directly observable and separated from that of bulk chlorophyll- We present an ultrafast transient absorption study of FR-PSII, investigating energy transfer and charge separation processes. Results show a rapid subpicosecond energy transfer from chlorophyll- to the long-wavelength chlorophylls- The data demonstrate the decay of an ∼720-nm negative feature on the picosecond-to-nanosecond timescales, coinciding with charge separation, secondary electron transfer, and stimulated emission decay.

Excited State Frequencies of Chlorophyll f and Chlorophyll a and Evaluation of Displacement through Franck-Condon Progression Calculations.

We present ground and excited state frequency calculations of the recently discovered extremely red-shifted chlorophyll f. We discuss the experimentally available vibrational mode assignments of chlorophyll f and chlorophyll a which are characterised by particularly large downshifts of 13¹-keto mode in the excited state. The accuracy of excited state frequencies and their displacements are evaluated by the construction of Franck-Condon (FC) and Herzberg-Teller (HT) progressions at the CAM-B3LYP/6-31G(d) level.

Femtosecond infrared spectroscopy of chlorophyll f-containing photosystem I.

The recent discovery of extremely red-shifted chlorophyll f pigments in both photosystem I (PSI) and photosystem II has led to the conclusion that chlorophyll f plays a role not only in the energy transfer, but also in the charge separation processes [Nürnberg et al., Science, 2018, 360, 1210-1213]. We have employed ultrafast transient infrared absorption spectroscopy to study the contribution of far-red light absorbing chlorophyll f to energy transfer and charge separation processes in far-red light-grown PSI (FRL-PSI) from the cyanobacterium Chroococcidiopsis thermalis PCC 7203.