Ultrafast, multi-dimensional infrared (IR) spectroscopy has been advanced in recent years to a versatile analytical tool with a broad range of applications to elucidate molecular structure on ultrafast timescales, and it can be used for samples in a many different environments. Following a short and general introduction on the benefits of 2D IR spectroscopy, the first part of this chapter contains a brief discussion on basic descriptions and conceptual considerations of 2D IR spectroscopy. Outstanding classical applications of 2D IR are used afterwards to highlight the strengths and basic applicability of the method. This includes the identification of vibrational coupling in molecules, characterization of spectral diffusion dynamics, chemical exchange of chemical bond formation and breaking, as well as dynamics of intra- and intermolecular energy transfer for molecules in bulk solution and thin films. In the second part, several important, recently developed variants and new applications of 2D IR spectroscopy are introduced. These methods focus on (i) applications to molecules under two- and three-dimensional confinement, (ii) the combination of 2D IR with electrochemistry, (iii) ultrafast 2D IR in conjunction with diffraction-limited microscopy, (iv) several variants of non-equilibrium 2D IR spectroscopy such as transient 2D IR and 3D IR, and (v) extensions of the pump and probe spectral regions for multi-dimensional vibrational spectroscopy towards mixed vibrational-electronic spectroscopies. In light of these examples, the important open scientific and conceptual questions with regard to intra- and intermolecular dynamics are highlighted. Such questions can be tackled with the existing arsenal of experimental variants of 2D IR spectroscopy to promote the understanding of fundamentally new aspects in chemistry, biology and materials science. The final part of the chapter introduces several concepts of currently performed technical developments, which aim at exploiting 2D IR spectroscopy as an analytical tool. Such developments embrace the combination of 2D IR spectroscopy and plasmonic spectroscopy for ultrasensitive analytics, merging 2D IR spectroscopy with ultra-high-resolution microscopy (nanoscopy), future variants of transient 2D IR methods, or 2D IR in conjunction with microfluidics. It is expected that these techniques will allow for groundbreaking research in many new areas of natural sciences.

近年来，超快速多维红外（IR）光谱技术已发展成为一种多功能分析工具，具有广泛的应用范围，可阐明超快速时标上的分子结构，并且可用于许多不同环境中的样品。在简要介绍了二维红外光谱的优点之后，本章的第一部分简要讨论了二维红外光谱的基本描述和概念性考虑。随后，使用2D IR的出色经典应用程序来突出该方法的优势和基本适用性。其中包括识别分子中的振动耦合，表征光谱扩散动力学，化学键形成和断裂的化学交换，以及本体溶液和薄膜中分子的分子内和分子间能量转移动力学。在第二部分中，介绍了一些重要的，最近开发的2D红外光谱的变体和新应用。这些方法着重于（i）在二维和三维约束下的分子应用，（ii）2D IR与电化学的结合，（iii）超快2D IR与衍射极限显微镜相结合，（iv）几种变体非平衡2D红外光谱，例如瞬态2D红外和3D红外，以及（v）泵浦和探测光谱区域的扩展，用于多维振动光谱向混合振动电子光谱学的方向发展。根据这些示例，强调了有关分子内和分子间动力学的重要开放科学和概念性问题。可以使用现有的2D红外光谱实验变体来解决这些问题，以促进对化学，生物学和材料科学领域新的根本方面的理解。本章的最后部分介绍了当前进行的技术开发的几个概念，这些概念旨在利用2D红外光谱作为分析工具。这些发展包括将2D IR光谱学和等离子光谱学结合起来用于超灵敏分析，将2D IR光谱学与超高分辨率显微镜（纳米技术），瞬态2D IR方法的未来变体或2D IR与微流体技术相结合。