Isolating in-crystallo reaction intermediates during 4+4 light-driven cycloaddition

Pentiptycene-anthracene (PAn-OCn) crystals are an ideal platform for delving into the fundamental aspects of in crystallo photochemical processes due to their light-driven [4+4] cycloadditive chemistry. In our previous experiments at the ESRF we used the unusual setup at the FIP2 (BM07) beamline, where an online microspectrophotometer is built perpendicularly to the X-ray beamline, to conduct simultaneous fluorescence and X-ray diffraction experiments with a time-resolution of ~30 seconds. From these, and based on a variety of analytical techniques, we observed the structural/kinetic features of PAn-OCn chemistry. Most importantly, our data suggested the presence of a reaction intermediate, which, due to low occupancy and short life-time, we could not structurally characterize. Thus, we propose to repeat our PAn-Ocn experiments at the ESRF at a higher time-resolution to determine the nature of the reaction intermediate.

五并蒽（Pentiptycene-anthracene，简称PAn-OCn）晶体因具备光驱动[4+4]环加成反应特性，是研究晶体内光化学过程基础机制的理想模型体系。此前我们在欧洲同步辐射装置（European Synchrotron Radiation Facility, ESRF）的FIP2（BM07）光束线站开展实验时，采用了该线站的非常规配置：将在线显微分光光度计垂直于X射线光束线搭建，以此实现时间分辨率约30秒的荧光与X射线衍射同步采集实验。基于上述实验及多种分析手段，我们揭示了PAn-OCn光化学反应的结构与动力学特征。尤为关键的是，实验数据表明该反应存在一种反应中间体，但由于其占位率较低且寿命极短，我们未能完成其结构表征。因此，我们提议在欧洲同步辐射装置提升时间分辨率，重复开展PAn-OCn相关实验，以明确该反应中间体的本质。