Variation of Exciton-Vibrational Coupling in Photosystem II Core Complexes from Thermosynechococcus elongatus As Revealed by Single-Molecule Spectroscopy

Abstract

The spectral properties and dynamics of the fluorescence emission of photosystem II core complexes are investigated by single-molecule spectroscopy at 1.6 K. The emission spectra are dominated by sharp zero-phonon lines (ZPLs). The sharp ZPLs are the result of weak to intermediate exciton-vibrational coupling and slow spectral diffusion. For several data sets, it is possible to surpass the effect of spectral diffusion by applying a shifting algorithm. The increased signal-to-noise ratio enables us to determine the exciton-vibrational coupling strength (Huang–Rhys factor) with high precision. The Huang–Rhys factors vary between 0.03 and 0.8. The values of the Huang–Rhys factors show no obvious correlation between coupling strength and wavelength position. From this result, we conclude that electrostatic rather than exchange or dispersive interactions are the main contributors to the exciton-vibrational coupling in this system.

Structural basis of light‐harvesting in the photosystem II core complex

“…To understand the significance of PsbH in the context of light‐harvesting, we have to consider low‐energy states that have been discovered in many photosynthetic systems as reviewed by Reimers et al These states become manifest in optical absorptions energetically well below that of the RC, that is, in the case of PSII at wavelengths larger than about 680 nm (see also the discussion of the RC absorption spectrum below). A distinction has to be made between extremely red‐shifted states of yet unknown origin and more moderately red‐shifted states giving rise to absorption at 694 nm as well as corresponding emission signals . We are only concerned with the latter type of states here.…”

The quest for energy traps in the CP43 antenna of photosystem II

“…The studies on the latter process have a long history, and different views emerged of how it proceeds in detail as reviewed in earlier work [7,8]. To distinguish between different possible EET mechanisms, it is necessary to link two different lines of research: On one hand, there is a myriad of spectroscopic data gathered over the years including stationary and time-resolved optical spectra [9][10][11][12][13][14][15][16][17][18][19], spectral hole-burning (HB) [20][21][22][23][24], and single molecule spectroscopy (SMS) [25,26]. On the other hand, the spatial structure of cyanobacterial PSIIcc was elucidated by X-ray crystallography from the first 3D structure in 2001 [27] via several refinements [28][29][30][31] until the most recent structures at 2.9 Å…”

Recent advances in single-molecule spectroscopy studies on light-harvesting processes in oxygenic photosynthesis

“…Chen et al recommended using the PSII CC samples obtained by re-solubilization of the PCII CC crystals. However, Skandary et al later reported an SMS study using the re-solubilized PSII CC crystal sample and confirmed no difference from the previous study [ 89 ]. Thus, the reduced red-most Chl emissions in the single PSII CC spectra are most probably due to the accumulation of the triplet state of the neighboring β-carotene molecule.…”

“…The Brecht group also pioneered SMS studies for PSII [ 88 , 89 ]. As for PSI, they determined the intensity ratio of I ZPL /( I ZPL + I PW ) to estimate the Huang–Rhys factor S of the emitting pigment.…”

“…They used a similar algorism to correct the spectral diffusion to that used for the analysis of the single PSI spectra. The estimated S values were distributed over a wide range from 0.03 to 0.8, suggesting wide inhomogeneity in the environment of the emitting pigment [ 89 ]. On the other hand, the S values estimated for the PSII CC were much smaller than those for PSI and never exceeded 1.0 for the ZPL located at up to 700 nm.…”