Hidden Vibronic and Excitonic Structure and Vibronic Coherence Transfer in the Bacterial Reaction Center

TL;DR

This study uses 2D electronic spectroscopy and simulations to uncover hidden vibronic and excitonic structures in the bacterial reaction center, revealing coherence transfer processes and resonances relevant to photosynthesis.

Contribution

It provides the first detailed experimental and theoretical analysis of vibronic and excitonic coherence in the bacterial reaction center, including identification of nonsecular coherence transfer.

Findings

Identification of specific excitonic and vibronic signatures

Support for nonsecular vibronic coherence transfer processes

Discovery of multiple intramolecular vibrational resonances

Abstract

We report two-dimensional electronic spectroscopy (2DES) experiments on the bacterial reaction center (BRC) from purple bacteria, revealing hidden excitonic and vibronic structure. Through analysis of the coherent dynamics of the BRC we resolve specific coherent signatures that allow us to definitively assign the upper exciton energy of the "special pair." This assignment is supported by simulations of coherent dynamics of a reduced excitonic model of the BRC. The simulations also identify nonsecular vibronic coherence transfer processes neglected in standard models of photosynthetic energy transfer and charge separation. In addition, the coherent dynamics reveal multiple quasi-resonances between key intramolecular pigment vibrations and excited state energy gaps in the BRC. The functional significance of such electronic-vibrational resonances for photosynthetic energy transfer and charge separation remains an open question.