Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
J Phys Chem A. 2014 May 1;118(17):3112-9. doi: 10.1021/jp5018554. Epub 2014 Apr 20.
This work demonstrates the use of triply resonant sum frequency (TRSF) spectroscopy as a "resonance IR" analogue to resonance Raman spectroscopy. TRSF is a four-wave-mixing process where three lasers with independent frequencies interact coherently with a sample to generate an output at their triple summation frequency. The first two lasers are in the infrared and result in two vibrational excitations, while the third laser is visible and induces a two-quantum anti-Stokes resonance Raman transition. The signal intensity grows when the laser frequencies are all in resonance with coupled vibrational and electronic states. The method therefore provides electronic enhancement of IR-active vibrational modes. These modes may be buried beneath solvent in the IR spectrum and also be Raman-inactive and therefore inaccessible by other techniques. The method is presented on the centrosymmetric complex copper phthalocyanine tetrasulfonate. In this study, the two vibrational frequencies were scanned across ring-breathing modes, while the visible frequency was left in resonance with the copper phthalocyanine tetrasulfonate Q band, resulting in a two-dimensional infrared plot that also reveals coupling between vibrational states. TRSF has the potential to be a very useful probe of structurally similar biological motifs such as hemes, as well as synthetic transition-metal complexes.
这项工作展示了三重共振和频（TRSF）光谱作为共振拉曼光谱的“共振红外”类似物的应用。TRSF 是一个四波混频过程，其中三个具有独立频率的激光与样品相干地相互作用，以在它们的三倍和频率处产生输出。前两个激光在红外区，导致两个振动激发，而第三个激光是可见的，并诱导双量子反斯托克斯共振拉曼跃迁。当激光频率都与耦合的振动和电子态共振时，信号强度会增加。因此，该方法提供了对 IR 活性振动模式的电子增强。这些模式可能被溶剂埋藏在红外光谱中，并且是拉曼非活性的，因此无法通过其他技术访问。该方法在对称中心配合物铜酞菁四磺酸盐上进行了介绍。在本研究中，两个振动频率在环呼吸模式上进行了扫描，而可见频率与铜酞菁四磺酸盐 Q 带保持共振，得到了一个二维红外图谱，也揭示了振动态之间的耦合。TRSF 有可能成为一种非常有用的探针，用于研究结构相似的生物基序，如血红素，以及合成的过渡金属配合物。
