Cole Jacqueline M
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, UK.
Chem Soc Rev. 2004 Oct 20;33(8):501-13. doi: 10.1039/b205339j. Epub 2004 Sep 13.
This tutorial review gathers together the recent developments in single-crystal X-ray diffraction that are starting to enable one to quantify directly the nature of light-induced electronic perturbations in chemical structures. Such structural information is key to understanding many photo-activated chemical processes and physical properties, and a description of the scientific impetus behind this incipient area of structural science, from academic and industrial perspectives, is given. Photoisomerism processes, solid-state photochemical reactions and spin-cross-over magnetic transitions, that have long-lived or irreversible light-induced states, are best understood by unravelling their three-dimensional structures measured in situ in their photo-converted state. A review of steady-state laser-induced single-crystal X-ray diffraction studies conducted, to date, and the experimental methodologies used in order to realise such structures, is presented. The structural characterisation of more transient photo-induced species (down to picosecond lifetimes) is paramount to a better understanding of the materials that undergo high-speed electronic switching, which make operative much of the electronics and optics industry, since there exists an inherent relationship between the excited-state structure and the physical properties exhibited. Prime examples include excited-state structures of molecular conductors and luminescent materials with potential applications as molecular wires, light-emitting diodes, non-linear optics, triboluminescence and electroluminescence. Previously, only indirect and qualitative interpretations of the nature of these excited-states could be formulated via spectroscopic techniques, but the developments in ms-ps time-resolved laser pump, X-ray probe single-crystal diffraction techniques, described herein, are overcoming this barrier, affording results that are entirely quantitative via a three-dimensional structural representation. In this regard, a review of structures of transient species studied to date is presented along with a discussion of the key experimental parameters that are required for a successful experiment, in terms of the X-ray, laser and sample characteristics. The importance of auxiliary spectroscopic work and complementary theoretical calculations is also briefly discussed. The paper concludes with a future outlook on new possible X-ray sources that will facilitate such work and extend it to structural studies on even more ephemeral species in the future.
本教程综述汇集了单晶X射线衍射的最新进展，这些进展开始使人们能够直接量化化学结构中光诱导电子扰动的性质。此类结构信息是理解许多光活化化学过程和物理性质的关键，本文从学术和工业角度对这一新兴结构科学领域背后的科学推动力进行了描述。光异构化过程、固态光化学反应和自旋交叉磁跃迁具有长寿命或不可逆的光诱导态，通过揭示其在光转换状态下原位测量的三维结构，能得到最好的理解。本文介绍了迄今为止进行的稳态激光诱导单晶X射线衍射研究以及为实现此类结构所使用的实验方法。对更短暂的光诱导物种（寿命短至皮秒）进行结构表征对于更好地理解经历高速电子开关的材料至关重要，这些材料在电子和光学工业中发挥着重要作用，因为激发态结构与所表现出的物理性质之间存在内在关系。主要例子包括分子导体和发光材料的激发态结构，它们具有作为分子导线、发光二极管、非线性光学、摩擦发光和电致发光的潜在应用。以前，只能通过光谱技术对这些激发态的性质进行间接和定性的解释，但本文所述的毫秒至皮秒时间分辨激光泵浦、X射线探测单晶衍射技术的发展正在克服这一障碍，通过三维结构表示提供完全定量的结果。在这方面，本文介绍了迄今为止研究的瞬态物种的结构，并讨论了就X射线、激光和样品特性而言成功实验所需的关键实验参数。还简要讨论了辅助光谱工作和补充理论计算的重要性。本文最后展望了新的可能的X射线源，这些源将促进此类工作，并在未来将其扩展到对更短暂物种的结构研究。
