Two-dimensional electronic spectroscopy of the Qx to Qy relaxation of chlorophylls a in photosystem II core complex

J Chem Phys. 2022 Apr 14;156(14):145102. doi: 10.1063/5.0079500.

Abstract

Using two-dimensional electronic spectroscopy, we measured the Qx to Qy transfer dynamics of the chlorophyll a (Chl a) manifold in the photosystem II (PSII) monomeric core complex from Arabidopsis thaliana. A PSII monomeric core consists of 35 Chls a and no Chl b, thus allowing for a clear window to study Chl a Qx dynamics in a large pigment-protein complex. Initial excitation in the Qx band results in a transfer to the Qy band in less than 60 fs. Upon the ultrafast transfer, regardless of the excitation frequency within the Qx band, the quasi-transient absorption spectra are very similar. This observation indicates that Chl a's Qx to Qy transfer is not frequency selective. Using a simple model, we determined that this is not due to the lifetime broadening of the ultrafast transfer but predominantly due to a lack of correlation between the PSII core complex's Chl a Qx and Qy bands. We suggest the origin to be the intrinsic loss of correlation during the Qx to Qy internal conversion as observed in previous studies of molecular Chl a dissolved in solvents.

MeSH terms

  • Chlorophyll A
  • Chlorophyll* / chemistry
  • Electronics
  • Light-Harvesting Protein Complexes
  • Photosystem II Protein Complex* / chemistry
  • Spectrum Analysis / methods

Substances

  • Light-Harvesting Protein Complexes
  • Photosystem II Protein Complex
  • Chlorophyll
  • Chlorophyll A