Department of Chemistry, University of California, Berkeley, CA 94720; andPhysical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Department of Chemistry, University of California, Berkeley, CA 94720; andPhysical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
Proc Natl Acad Sci U S A. 2014 Jul 15;111(28):10061-6. doi: 10.1073/pnas.1409207111. Epub 2014 Jun 9.
Multidimensional nonlinear spectroscopy, in the electronic and vibrational regimes, has reached maturity. To date, no experimental technique has combined the advantages of 2D electronic spectroscopy and 2D infrared spectroscopy, monitoring the evolution of the electronic and nuclear degrees of freedom simultaneously. The interplay and coupling between the electronic state and vibrational manifold is fundamental to understanding ensuing nonradiative pathways, especially those that involve conical intersections. We have developed a new experimental technique that is capable of correlating the electronic and vibrational degrees of freedom: 2D electronic-vibrational spectroscopy (2D-EV). We apply this new technique to the study of the 4-(di-cyanomethylene)-2-methyl-6-p-(dimethylamino)styryl-4H-pyran (DCM) laser dye in deuterated dimethyl sulfoxide and its excited state relaxation pathways. From 2D-EV spectra, we elucidate a ballistic mechanism on the excited state potential energy surface whereby molecules are almost instantaneously projected uphill in energy toward a transition state between locally excited and charge-transfer states, as evidenced by a rapid blue shift on the electronic axis of our 2D-EV spectra. The change in minimum energy structure in this excited state nonradiative crossing is evident as the central frequency of a specific vibrational mode changes on a many-picoseconds timescale. The underlying electronic dynamics, which occur on the hundreds of femtoseconds timescale, drive the far slower ensuing nuclear motions on the excited state potential surface, and serve as a excellent illustration for the unprecedented detail that 2D-EV will afford to photochemical reaction dynamics.
多维非线性光谱学，在电子和振动领域，已经成熟。迄今为止，没有一种实验技术能够结合二维电子光谱学和二维红外光谱学的优势，同时监测电子和核自由度的演化。电子态和振动模态之间的相互作用和耦合对于理解随后的非辐射途径至关重要，特别是那些涉及锥形交叉的途径。我们已经开发出一种新的实验技术，能够关联电子和振动自由度：二维电子-振动光谱学（2D-EV）。我们将这项新技术应用于研究 4-(二氰基亚甲基)-2-甲基-6-p-(二甲氨基)苯乙烯基-4H-吡喃（DCM）激光染料在氘代二甲亚砜中的激发态弛豫途径。从 2D-EV 光谱中，我们阐明了在激发态势能面上的弹道机制，其中分子几乎瞬间向上在能量上向上投影到局部激发和电荷转移态之间的过渡态，正如我们的 2D-EV 光谱中电子轴上的快速蓝移所证明的那样。在这个激发态非辐射交叉中，最低能量结构的变化是明显的，因为特定振动模式的中心频率在许多皮秒时间尺度上发生变化。在数百飞秒时间尺度上发生的基本电子动力学驱动了在激发态势能表面上随后的核运动的慢得多，并且为 2D-EV 将为光化学反应动力学提供的前所未有的细节提供了一个极好的例证。
