Non-Uniform Excited State Electronic-Vibrational Coupling of Pigment–Protein Complexes,The Journal of Physical Chemistry Letters

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Non-Uniform Excited State Electronic-Vibrational Coupling of Pigment–Protein Complexes
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2020-11-25 , DOI: 10.1021/acs.jpclett.0c02454
Shawn Irgen-Gioro ₁ , Karthik Gururangan _{1,

2} , Austin P. Spencer ₁ , Elad Harel _{1,

2}

Affiliation

Photosynthetic organisms exploit interacting quantum degrees of freedom, namely intrapigment electron-vibrational (vibronic) and interpigment dipolar couplings (J-coupling), to rapidly and efficiently convert light into chemical energy. These interactions result in wave function configurations that delocalize excitation between pigments and pigment vibrations. Our study uses multidimensional spectroscopy to compare two model photosynthetic proteins, the Fenna–Matthews Olson (FMO) complex and light harvesting 2 (LH2), and confirm that long-lived excited state coherences originate from the vibrational modes of the pigment. Within this framework, the J-coupling of vibronic pigments should have a cascading effect in modifying the structured spectral density of excitonic states. We show that FMO effectively couples all of its excitations to a uniform set of vibrations while in LH2, its two chromophore rings each couple to a unique vibrational environment. We simulate energy transfer in a simple model system with non-uniform vibrational coupling to demonstrate how modification of the vibronic coupling strength can modulate energy transfer. Because increasing vibronic coupling increases internal relaxation, strongly coupled vibronic states can act as an energy funnel, which can potentially benefit energy transport.

中文翻译：

颜料-蛋白质复合物的非均匀激发态电子振动耦合

光合生物利用相互作用的量子自由度，即内嵌电子振动（振动）和颜料间偶极耦合（J耦合），将光快速有效地转换为化学能。这些相互作用导致波动函数配置使颜料之间的激发和颜料振动离域。我们的研究使用多维光谱法比较了两种模型光合蛋白，即Fenna-Matthews Olson（FMO）复合物和光收集2（LH2），并确认了长寿命激发态的相干性源自颜料的振动模式。在此框架内，J-振动子颜料的偶联应具有级联作用，以改变激子态的结构光谱密度。我们表明，FMO有效地将其所有激发耦合到一组均匀的振动上，而在LH2中，其两个生色环分别耦合到一个独特的振动环境。我们在具有不均匀振动耦合的简单模型系统中模拟能量传递，以演示对振动耦合强度的修改如何调节能量传递。因为增加的电子振动耦合会增加内部弛豫，所以强耦合的电子振动态可以充当能量漏斗，从而可能有益于能量传输。

更新日期：2020-12-17

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