Karki Khadga J, Chen Junsheng, Sakurai Atsunori, Shi Qi, Gardiner Alastair T, Kühn Oliver, Cogdell Richard J, Pullerits Tönu
Chemical Physics and NanoLund , Lund University , Box 124 , 22100 Lund , Sweden . Email:
Institute of Industrial Science , The University of Tokyo , 4-6-1 Komaba, Meguro , Tokyo 153-8505 , Japan.
Chem Sci. 2019 Jul 4;10(34):7923-7928. doi: 10.1039/c9sc01888c. eCollection 2019 Sep 14.
Electronic 2D spectroscopy allows nontrivial quantum effects to be explored in unprecedented detail. Here, we apply recently developed fluorescence detected coherent 2D spectroscopy to study the light harvesting antenna 2 (LH2) of photosynthetic purple bacteria. We report double quantum coherence 2D spectra which show clear cross peaks indicating correlated excitations. Similar results are found for rephasing and nonrephasing signals. Analysis of signal generating quantum pathways leads to the conclusion that, contrary to the currently prevailing physical picture, the two weakly coupled pigment rings of LH2 share the initial electronic excitation leading to quantum mechanical correlation between the two clearly separate absorption bands. These results are general and have consequences for the interpretation of initially created excited states not only in photosynthesis but in all light absorbing systems composed of weakly interacting pigments where the excitation transfer is commonly described by using Förster theory. Being able to spectrally resolve the nonequilibrium dynamics immediately following photoabsorption may provide a glimpse to the systems' transition into the Förster regime.
电子二维光谱能够以前所未有的细节探索非平凡量子效应。在此，我们应用最近开发的荧光检测相干二维光谱来研究光合紫色细菌的光捕获天线2（LH2）。我们报告了双量子相干二维光谱，其显示出清晰的交叉峰，表明存在相关激发。在重相位和非重相位信号中也发现了类似结果。对产生信号的量子路径的分析得出结论，与当前流行的物理图像相反，LH2的两个弱耦合色素环共享初始电子激发，导致两个明显分开的吸收带之间存在量子力学相关性。这些结果具有普遍性，不仅对光合作用中初始产生的激发态的解释有影响，而且对所有由弱相互作用色素组成的光吸收系统也有影响，在这些系统中，激发转移通常用福斯特理论来描述。能够在光吸收后立即光谱分辨非平衡动力学，可能会让我们瞥见系统向福斯特 regime 的转变。
