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

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.

23 pages, 5 figures, submitted to Nature Communications

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• Light-harvesting efficiency cannot depend on optical coherence in the absence of orientational order
• Observing Quantum Coherent Oscillations in a Three-Level Atoms via Electromagnetically Induced Transparency by Two-Dimensional Spectroscopy
• Vibronic Resonance Along Effective Modes Mediates Selective Energy Transfer in Excitonically Coupled Aggregates