Cupellini Lorenzo, Caprasecca Stefano, Guido Ciro A, Müh Frank, Renger Thomas, Mennucci Benedetta
Dipartimento di Chimica e Chimica Industriale , University of Pisa , via G. Moruzzi 13 , 56124 Pisa , Italy.
Institute of Theoretical Physics, Department of Theoretical Biophysics , Johannes Kepler University Linz , Altenberger Strasse 69 , 4040 Linz , Austria.
J Phys Chem Lett. 2018 Dec 6;9(23):6892-6899. doi: 10.1021/acs.jpclett.8b03233. Epub 2018 Nov 26.
The photosynthetic apparatus of purple bacteria uses exciton delocalization and static disorder to modulate the position and broadening of its absorption bands, leading to efficient light harvesting. Its main antenna complex, LH2, contains two rings of identical bacteriochlorophyll pigments, B800 and B850, absorbing at 800 and 850 nm, respectively. It has been an unsolved problem why static disorder of the strongly coupled B850 ring is several times larger than that of the B800 ring. Here we show that mixing between excitons and charge transfer states in the B850 ring is responsible for the effect. The linear absorption spectrum of the LH2 system is simulated by using a multiscale approach with an exciton Hamiltonian generalized to include the charge transfer states that involve adjacent pigment pairs, with static disorder modeled microscopically by molecular dynamics simulations. Our results show that sufficient inhomogeneous broadening of the B850 band, needed for efficient light harvesting, is only obtained by utilizing static disorder in the coupling between local excited and interpigment charge transfer states.
紫色细菌的光合装置利用激子离域和静态无序来调节其吸收带的位置和展宽，从而实现高效的光捕获。其主要天线复合体LH2包含两个相同的细菌叶绿素色素环，即B800和B850，分别在800纳米和850纳米处吸收光。强耦合的B850环的静态无序比B800环的静态无序大几倍，这一直是一个未解决的问题。在此我们表明，B850环中激子与电荷转移态之间的混合是造成这种效应的原因。通过使用多尺度方法模拟LH2系统的线性吸收光谱，该方法采用了广义的激子哈密顿量，以包括涉及相邻色素对的电荷转移态，并通过分子动力学模拟微观地模拟静态无序。我们的结果表明，高效光捕获所需的B850带足够的非均匀展宽，只有通过利用局部激发态与色素间电荷转移态之间耦合中的静态无序才能获得。
