Excitation energy transfer can be unusually efficient and structurally robust when mediated by molecular excitons, which arise in a photosynthetic light-harvesting protein when delocalized excitations of the electronic chromophores are created upon absorption of light. Here we report results from two-dimensional electronic spectroscopy and electronic structure calculations, revealing that excitation energy is transferred between the peridinin and chlorophyll excitons in the peridinin-chlorophyll protein from marine dinoflagellates over a delocalized, two-step pathway. Upon absorption of light by the peridinins in the strong, mid-visible absorption band, excitation energy is trapped by the chlorophylls in less than 50 fs at room temperature. The overall process is slowed only by a few fs upon replacement of chlorophyll a with chlorophyll b. The key step in the pathway transfers excitation from higher-energy peridinin excitons with more extensive delocalization to the lowest-energy peridinin exciton, which is delocalized only over peridinin 614 and the neighboring chlorophyll.

当由分子激子介导时，激发能量转移可能异常有效且结构坚固，当通过吸收光而产生电子发色团的离域激发时，这种激发能转移会在光合作用的光捕获蛋白中产生。在这里，我们报告了二维电子光谱和电子结构计算的结果，揭示了激发能在海洋生物鞭毛虫的鞭毛蛋白-叶绿素蛋白中的鞭毛蛋白和叶绿素激子之间转移，经过了非定域的两步路径。在室温下，在不到50 fs的时间内，叶绿素捕获了皮兰德宁在强的中可见吸收带中吸收的光时，激发能就被叶绿素捕获了。更换叶绿素a时，整个过程只会减慢几fs叶绿素b。该途径中的关键步骤是将激发作用从能量更高的perdininin激子转移到更广泛的离域，再转移到能量最低的peridinin激子，后者仅在peridinin 614和附近的叶绿素上才离域。