SusChEM: Molecular Information and Crystal Control in Solid State Photochemical Reactivity

在化学系化学结构、动力学和机理B项目的资助下，加州大学洛杉矶分校化学和生物化学系的Miguel A. Garcia-Garibay教授正在建立新的合成策略，利用在晶体状态下发生的高阶和刚性反应，将简单的化学物质转化为更复杂、高价值的物质。他们的策略依赖于结构的选择，当被紫外线吸收激活时，这些结构会形成高度反应的中间体。通过在晶体状态下进行这些反应，而不是在液体状态下进行，他们能够获得几乎纯的固体产物，而不需要溶剂、催化剂或额外的试剂。该项目属于SusChEM组合，因为该反应不使用溶剂，也不需要能量来分离和去除副产物。这个项目为一些学生提供了一个极好的多学科训练基地。研究生和暑期本科生来自三个合作的黑人学院和大学机构：霍华德大学，克拉克亚特兰大大学和斯佩尔曼学院。通过选择产生高活性中间体的稳定分子，该项目实施了强大的策略来设计晶体中的反应，该项目解决了六取代酮的固态光脱羰基化以及三唑啉、吡唑啉和选定的芳香叠氮化物的光脱氮。自由基对、双自由基和亚硝基在高放热过程中由反应物的激发态在结晶状态下生成，并详细分析了它们的产物形成和动力学。在固体状态下，自由基-自由基结合反应与立体化学保留和选择性亚硝基插入发生。光化学反应是在表征良好的结晶相中进行的，通过热分析和光谱手段分析了它们从反应物的固相到产物的固相的转变。进行表征是为了确定相应的相图和清洁高效反应所需的条件。利用单晶x射线衍射获得的结构信息和悬浮在水中的纳米晶体激光闪光光解测量获得的动力学测量结果，探索了详细的反应机理。

With funding from the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Professor Miguel A. Garcia-Garibay of the Department of Chemistry and Biochemistry at the University of California-Los Angeles is establishing new synthetic strategies to transform simple chemicals into more complex, high value substances, by taking advantage of reactions that occur under the high order and rigidity of the crystalline state. Their strategy relies on the selection of structures that are known to form highly reactive intermediates when activated by the absorption of ultraviolet light. By executing those reactions in the crystalline state, instead of doing them in liquids, they are able to obtain nearly pure solid products with no need for solvents, catalysts or additional reagents. This project is in the SusChEM portfolio as the reactions do not use solvent and require no energy for the separation and removal of byproducts. This project provides an excellent multidisciplinary training ground for several students. Graduate students and summer undergraduates from three partnering Historically Black Colleges and Universities institutions: Howard University, Clark Atlanta University, and Spellman College, are involved. Having implemented robust strategies to engineer reactions in crystals by selecting stable molecules that generate highly reactive intermediates, this project addresses the solid state photodecarbonylation of hexasubstituted ketones and the photodenitrogenation of triazolines, pyrazolines, and selected aromatic azides. Radical pairs, biradicals, and nitrenes are generated in the crystalline state in highly exothermic processes from the excited state of the reactants, and their product formation and kinetics are analyzed in detail. In the solid state, radical-radical combination reactions with retention of stereochemistry, and selective nitrene insertions occur. Photochemical reactions are carried out in well-characterized crystalline phases and their transformations from the solid phase of the reactant to the solid phase of the product are analyzed by thermal analysis and spectroscopic means. This characterization is done in order to determine the corresponding phase diagrams and the conditions required for clean and efficient reactions. Detailed reaction mechanisms are explored by taking advantage of structural information available from single crystals X-ray diffraction and kinetic measurements obtained from laser flash photolysis measurements using nanocrystals suspended in water.