The Surface Diels-Alder Reaction of Tetracene and Pentacene Crystals; Blurring the Lines Between Solid State, Surface, and Synthetic Chemistry

本课题由化学系化学结构与动力学机制B项目资助，Jacob W.芝加哥洛约拉大学化学和生物化学系的西塞克研究典型有机半导体的表面化学：并四苯和并五苯。 由于这些材料与经典表面几乎没有相似之处，因此控制其反应性的规则需要本文研究的全新反应机制。 这些实验的结果使我们能够提高这些材料在下一代设备中的性能，包括小型显示器（例如智能手机屏幕）中的发光二极管和晶体管。 这笔赠款还支持他们的新兴科学家研讨会，该研讨会让高中生沉浸在主办实验室的实验中。 这个大量订阅的项目也作为赠款的一部分进行评估，并在德保罗大学作为试点扩大。更具体的科学，该项目着眼于三个领域，突出传统无机基质和分子晶体表面的化学之间的差异。 前两个中心的事实，几何考虑（基于在晶体中的分子取向）似乎是反应性的主要决定因素。 在第一部分中，一个表面腔的想法，周围的分子包围的反应位点，是发达国家解释并四苯和并五苯晶体的面之间的反应性差异。 通过X射线光电子能谱法评估随时间推移的覆盖率。 第二部分研究了反应腔如何也负责抑制半导体中最具反应性的键。 这表现在并四苯和并五苯晶体的不同表面上形成的不同区域异构体中。 基板和吸附参数（电子，空间位阻和相位）检查其对区域异构体形成的影响。 该项目的最后一部分研究了吸附物的行为是如何受到晶体的极低能量表面的影响。 由于表面能小于金属表面的十分之一，预计吸附物的覆盖率和停留时间在并五苯和并四苯上要低得多。 石英晶体微天平研究结合红外反射吸收光谱允许反应动力学与吸附质覆盖进一步的机械细化得到证实。

In this project, funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Jacob W. Ciszek of the Department of Chemistry and Biochemistry at Loyola University Chicago studies the surface chemistry of the prototypical organic semiconductors: tetracene and pentacene. Because these materials bear little resemblance to classical surfaces, the rules governing their reactivity require entirely new reaction mechanisms which are examined herein. The results from these experiments allow us to improve the performance of these materials in next generation devices including the light emitting diodes and transistors found in small displays (e.g. smartphone screens). This grant also supports their Emerging Scientists Workshop, which immerses high school students in experiments found in host laboratories. This heavily subscribed program is also evaluated as part of the grant, and is expanded as a pilot at DePaul University.More specific to the science, this project looks at three areas, which highlight differences between chemistry at traditional inorganic substrates and the surfaces of molecular crystals. The first two center on the fact that geometric considerations (based off molecular orientation in the crystal) appears to be the primary determinant of reactivity. In part one, the idea of a surface cavity, where surrounding molecules envelop the reactive loci, is developed to explain the reactivity differences between the faces of tetracene and pentacene crystals. Coverage is assessed over time via X-ray photoelectron spectroscopy. Part two examines how the reaction cavity is also responsible for inhibition of the most reactive bonds in the semiconductor. This manifests itself in different regioisomers formed on the various surfaces of tetracene and pentacene crystals. Both substrate and adsorbate parameters (electronic, steric, and phase) are examined for their impact on regioisomer formation. The final portion of the project examines how adsorbate behavior is impacted by the very low energy surface of the crystal. With surface energies less than a tenth of metallic surfaces, the coverage and residence time of the adsorbates are expected to be much lower on pentacene and tetracene. Quartz crystal microbalance studies in conjunction with infrared reflection absorption spectroscopy allow reaction kinetics to be corroborated with adsorbate coverage for further mechanistic refinement.