Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
Nat Commun. 2017 Mar 10;8:14732. doi: 10.1038/ncomms14732.
Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational-vibrational, electronic-vibrational and electronic-electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment-protein complexes.
电子和振动相关性报告了分子物种的动力学和结构，但实验揭示这些相关性极具挑战性。在这里，我们展示了一种方法，该方法可以通过量子相干选择性探测振动和电子简并中的状态之间的相关性。具体来说，我们测量了一个完全相干的四维光谱，该光谱同时编码了振动-振动、电子-振动和电子-电子相互作用。通过结合近脉冲共振和非共振激发，可以在没有不需要的低阶杂散信号的情况下测量溶液中复杂有机分子的所需五阶信号。该方法的一个关键特征是电子和振动频率分辨率，能够实现单个量子相干途径的隔离和分配。然后，在原本宽阔且无特征的二维电子光谱中揭示系统的振电子结构。该方法适用于研究在电子跃迁强烈耦合到声子和振动的情况下难以捉摸的量子效应，例如光合作用色素蛋白复合物中的能量转移。
