振动耦合解释了自然和人工光收集器中超快的类胡萝卜素到细菌叶绿素能量转移
Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters
摘要：
光合作用中的初始能量转移发生在捕光色素之间，并且在超快的时间尺度上。我们分析了类胡萝卜素细菌叶绿素的能量转移在LH 2 Marichromatium purpuratum以及在人工捕光二分体系统，通过使用瞬态光栅和二维电子光谱与10 fs的时间分辨率。我们发现，Förster型模型重现实验观察到的60 fs的转移时间，但高估了耦合常数，这导致了不一致的线性吸收和电子二维光谱。我们表明，一个振动模型，它把类胡萝卜素的电子地面和激发态的振动作为系统的哈密顿量的一部分，再现所有测量的量。重要的是，这里提出的电子振动模型可以解释快速的能量转移速率与只有适度的耦合常数，这是与基于结构的计算。反直觉地，类胡萝卜素电子基态上的振动能级在细菌叶绿素的激发态群体转移中起着核心作用，因为供体-受体能隙和振动基态能量之间的共振是这些系统中超快能量转移速率的物理基础。
英文摘要：
The initial energy transfer in photosynthesis occurs between the light-harvesting pigments and on ultrafast timescales. We analyze the carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium purpuratum as well as in an artificial light-harvesting dyad system by using transient grating and two-dimensional electronic spectroscopy with 10 fs time resolution. We find that Förster-type models reproduce the experimentally observed 60 fs transfer times, but overestimate coupling constants, which leads to a disagreement with both linear absorption and electronic 2D-spectra. We show that a vibronic model, which treats carotenoid vibrations on both electronic ground and excited state as part of the system's Hamiltonian, reproduces all measured quantities. Importantly, the vibronic model presented here can explain the fast energy transfer rates with only moderate coupling constants, which are in agreement with structure based calculations. Counterintuitively, the vibrational levels on the carotenoid electronic ground state play a central role in the excited state population transfer to bacteriochlorophyll as the resonance between the donor-acceptor energy gap and vibrational ground state energies is the physical basis of the ultrafast energy transfer rates in these systems.
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