Roscioli Jerome D, Ghosh Soumen, LaFountain Amy M, Frank Harry A, Beck Warren F
Department of Chemistry, Michigan State University , East Lansing, Michigan 48824-1322, United States.
Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269-3036, United States.
J Phys Chem Lett. 2017 Oct 19;8(20):5141-5147. doi: 10.1021/acs.jpclett.7b01791. Epub 2017 Oct 6.
It remains an open question whether quantum coherence and molecular excitons created by delocalization of electronic excited states are essential features of the mechanisms that enable efficient light capture and excitation energy transfer to reaction centers in photosynthetic organisms. The peridinin-chlorophyll a protein from marine dinoflagellates is an example of a light-harvesting system with tightly clustered antenna chromophores in which quantum coherence has long been suspected, but unusually it features the carotenoid peridinin as the principal light absorber for mid-visible photons. We report that broad-band two-dimensional electronic spectroscopy indeed reveals the initial presence of exciton relaxation pathways that enable transfer of excitation from peridinin to chlorophyll a in <20 fs, but the quantum coherence that permits this is very short-lived. Strongly coupled excited-state vibrational distortions of the peridinins trigger a dynamic transition of the electronic structure of the system and a rapid conversion to incoherent energy transfer mechanisms.
由电子激发态离域产生的量子相干性和分子激子是否是光合生物中实现高效光捕获和激发能向反应中心转移机制的基本特征,这仍然是一个悬而未决的问题。来自海洋甲藻的多甲藻叶绿素a蛋白是一种光捕获系统的例子,其中天线发色团紧密聚集,长期以来人们一直怀疑其中存在量子相干性,但不同寻常的是,它以类胡萝卜素多甲藻素作为中可见光光子的主要光吸收体。我们报告,宽带二维电子光谱确实揭示了激子弛豫途径的初始存在,这种途径能够在<20飞秒内将激发从多甲藻素转移到叶绿素a,但允许这种转移的量子相干性寿命非常短。多甲藻素强烈耦合的激发态振动畸变触发了系统电子结构的动态转变,并迅速转变为非相干能量转移机制。