Vibronic coupling between molecules has been recently discussed to play an important role in photosynthetic functions. Furthermore, this type of coupling between electronic states has been suggested to define photophysical properties of chlorophylls, a family of photosynthetic molecules. However, experimental investigation of vibronic coupling presents a major challenge. One subtle way to study this coupling is by excitation and observation of the superpositions of vibrational states via transitions to vibronically mixed states. Such superpositions, called coherences, are then observed as quantum beats in non-linear spectroscopy experiments. Here we present polarization-controlled two-dimensional electronic spectroscopy study of the chlorophyll c1 molecule at cryogenic (77 K) temperature. By applying complex analysis to the oscillatory signals we are able to unravel vibronic coupling in this molecule. The vibronic mixing picture that we see is much more complex than was thought before.

最近已经讨论了分子之间的振动耦合在光合作用中起重要作用。此外，已经提出了电子态之间的这种类型的耦合来定义叶绿素（一种光合分子家族）的光物理性质。然而，振动耦合的实验研究提出了一个重大挑战。研究这种耦合的一种微妙方式是通过激发和观察振动状态的叠加（通过过渡到振动混合态）。然后，在非线性光谱实验中，将这种称为相干的叠加观测为量子拍。在这里，我们介绍了叶绿素c1的偏振控制二维电子光谱研究分子在低温（77 K）温度下。通过对振荡信号进行复杂的分析，我们能够解开该分子中的振动耦合。我们看到的振动混合图像比以前想象的要复杂得多。