Quantum-coherent dynamics in photosynthetic charge separation revealed by wavelet analysis

TL;DR

This study uses wavelet analysis on 2D electronic spectroscopy data to reveal sustained quantum coherence in photosynthetic charge separation, highlighting coherence's role in efficient electron transfer in PSII RC.

Contribution

First application of wavelet analysis to 2DES data in photosynthesis, providing time-resolved insights into vibronic coherence during charge separation.

Findings

Coherence between excitons persists over 500 fs.

Coherence between exciton and charge-transfer states lasts at least 1 ps.

Coherence aids in sampling pathways and efficient electron transfer.

Abstract

Experimental/theoretical evidence for sustained vibration-assisted electronic (vibronic) coherence in the Photosystem II Reaction Center (PSII RC) indicates that photosynthetic solar-energy conversion might be optimized through the interplay of electronic and vibrational quantum dynamics. This evidence has been obtained by investigating the primary charge separation process in the PSII RC by two-dimensional electronic spectroscopy (2DES) and Redfield modeling of the experimental data. However, while conventional Fourier transform analysis of the 2DES data allows oscillatory signatures of vibronic coherence to be identified in the frequency domain in the form of static 2D frequency maps, the real-time evolution of the coherences is lost. Here we apply for the first time wavelet analysis to the PSII RC 2DES data to obtain time-resolved 2D frequency maps. These maps allow us to demonstrate that i) coherence between the excitons initiating the two different charge separation pathways is active for more than 500 fs, and ii) coherence between exciton and charge-transfer states, the reactant and product of the charge separation reaction, respectively, is active for at least 1 ps. These findings imply that the PSII RC employs coherence i) to sample competing electron transfer pathways, and ii) to perform directed, ultrafast and efficient electron transfer.