The quantum mystery of photosynthesis may be a vibrational illusion
In short: For years, scientists debated whether plants use quantum coherence to move energy with perfect efficiency. New research using polarization-controlled 2D spectroscopy suggests the answer is more grounded: while electronic coherences vanish almost instantly, long-lived vibrations dominate the complex's behavior.
The Fenna–Matthews–Olson (FMO) complex of green sulfur bacteria has served as a primary model for studying biological energy transfer. Because it is a water-soluble pigment-protein complex with a trimeric structure, researchers have long sought to understand how it mediates excitation energy from light-harvesting chlorosomes to bacterial reaction centers. The debate centered on whether 'quantum beats'—oscillations in the spectra—represented electronic coherences that allowed for efficient, wavelike energy transport.
Recent characterization using polarization-controlled 2D spectroscopy and vibronic exciton modeling has clarified these signals. The study reveals that electronic coherences dephase extremely rapidly, completing their decay within 240 fs even at a temperature of 77 K. In contrast, the long-lived quantum beats observed in previous studies are exclusively vibrational in origin, originating from both ground- and excited-state vibrations.
However, this does not mean vibrations are irrelevant to the process. Vibronically linked excited states are shown to generate particular vibrational coherences by this study. This suggests that while the 'quantum' nature of the energy transfer isn't driven by electronic coherence as once thought, vibronic coupling remains a significant mechanism in how photosynthetic systems manage energy flow.
This distinction matters because it refines our understanding of biological efficiency. It moves the narrative away from a purely exotic quantum-mechanical transport model toward one where protein environments and vibrational dynamics play a decisive role in shaping the energy landscape of life.
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Sources
- Summary by Intellect · source: Identification and characterization of diverse coherences in the Fenna–Matthews–Olson complex - Nature Chemistry
- Also: Fenna–Matthews–Olson complex
- Also: Identification and characterization of diverse coherences in the Fenna–Matthews–Olson complex
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