Consistent Model of Ultrafast Energy Transfer in Peridinin Chlorophyll- a Protein Using Two-Dimensional Electronic Spectroscopy and Förster Theory

J Phys Chem B. 2019 Aug 1;123(30):6410-6420. doi: 10.1021/acs.jpcb.9b04324. Epub 2019 Jul 19.

Abstract

Solar light harvesting begins with electronic energy transfer in structurally complex light-harvesting antennae such as the peridinin chlorophyll-a protein from dinoflagellate algae. Peridinin chlorophyll-a protein is composed of a unique combination of chlorophylls sensitized by carotenoids in a 4:1 ratio, and ultrafast spectroscopic methods have previously been utilized in elucidating their energy-transfer pathways and timescales. However, due to overlapping signals from various chromophores and competing pathways and timescales, a consistent model of intraprotein electronic energy transfer has been elusive. Here, we used a broad-band two-dimensional electronic spectroscopy, which alleviates the spectral congestion by dispersing excitation and detection wavelengths. Interchromophoric couplings appeared as cross peaks in two-dimensional electronic spectra, and these spectral features were observed between the peridinin S2 states and chlorophyll-a Qx and Qy states. In addition, the inherently high time and frequency resolutions of two-dimensional electronic spectroscopy enabled accurate determination of the ultrafast energy-transfer dynamics. Kinetic analysis near the peridinin S1 excited-state absorption, which forms in 24 fs after optical excitation, reveals an ultrafast energy-transfer pathway from the peridinin S2 state to the chlorophyll-a Qx state, a hitherto unconfirmed pathway critical for fast interchromophoric transfer. We propose a model of ultrafast peridinin chlorophyll-a protein photophysics that includes (1) a conical intersection between peridinin S2 and S1 states to explain both the ultrafast peridinin S1 formation and the residual peridinin S2 population for energy transfer to chlorophyll-a, and (2) computationally and experimentally derived peridinin S2 site energies that support the observed ultrafast peridinin S2 to chlorophyll-a Qx energy transfer.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Carotenoids / chemistry*
  • Chlorophyll A / chemistry*
  • Chlorophyll A / metabolism
  • Dinoflagellida / chemistry*
  • Dinoflagellida / metabolism
  • Energy Transfer
  • Kinetics
  • Models, Chemical
  • Spectrum Analysis / methods*
  • Thermodynamics

Substances

  • peridinin
  • Carotenoids
  • Chlorophyll A