Coherence and population dynamics of chlorophyll excitations in FCP complex: Two-dimensional spectroscopy study

TL;DR

This study used two-dimensional spectroscopy at 77 K to investigate energy transfer and coherence in the fucoxanthin-chlorophyll protein complex, revealing vibrational influences and new chlorophyll c states involved in energy transfer.

Contribution

It provides new insights into the spectral dynamics and identifies previously unrecognized chlorophyll c states participating in energy transfer within the complex.

Findings

Identification of intramolecular vibrations dominating early coherence dynamics

Discovery of non-interacting chlorophyll c states involved in energy transfer

Hypothesis of vibrations-assisted coherent energy transfer mechanisms

Abstract

The energy transfer processes and coherent phenomena in the fucoxanthin-chlorophyll protein complex, which is responsible for the light harvesting function in marine algae diatoms, were investigated at 77 K by using two-dimensional electronic spectroscopy. Experiments performed on the femtosecond and picosecond timescales led to separation of spectral dynamics, witnessing evolutions of coherence and population states of the system in the spectral region of ${\rm Q}_{y}$ transitions of chlorophylls $a$ and $c$. Analysis of the coherence dynamics allowed us to identify chlorophyll (Chl) $a$ and fucoxanthin intramolecular vibrations dominating over the first few picoseconds. Closer inspection of the spectral region of the ${\rm Q}_{y}$ transition of Chl $c$ revealed previously not identified mutually non-interacting chlorophyll $c$ states participating in femtosecond or picosecond energy transfer to the Chl $a$ molecules. Consideration of separated coherent and incoherent dynamics allowed us to hypothesize the vibrations-assisted coherent energy transfer between Chl $c$ and Chl $a$ and the overall spatial arrangement of chlorophyll molecules.