Novel Cation Radical and Exciplex Chemistry

通过这个奖项，化学结构、动力学和机理B项目将支持罗切斯特大学的Joseph P. Dinnocenzo教授研究在温和条件下高活性芳基自由基的选择性形成。从这些研究中获得的机理见解可以为在合成和新材料设计中合理利用化学提供必要的知识。此外，对新发现的阳离子复合物和双发射复合物的研究将为这些新的激发态中间体提供知识。更好地了解这些杂合中间体的基本光物理性质的研究将为设计有效的光诱导电子转移反应和在传感应用中的潜在应用提供有价值的知识。学生同事将学习进行化学合成和进行光化学的机理研究。包括一系列不太传统的技术（荧光测定法、瞬态吸收光谱、时间相关单光子计数、电化学和现代计算方法）。因此，在美国国家科学基金会支持下训练的学生将为在他们的专业科学生涯中解决各种多学科问题做好充分的准备。该项目还将通过罗切斯特大学的NSF REU暑期项目使本科生受益，特别关注从传统上未被充分代表的科学和工程群体中招募学生。Dinnocenzo实验室最近的工作表明，芳基三烷基锡烷阳离子自由基经历亲核试剂辅助的断裂反应，其中不太稳定的芳基自由基往往比更稳定的烷基自由基更容易形成，这似乎是一个逆向热力学的结果。这种选择性在离子自由基化学中是前所未有的。拟议的研究将通过合成、稳态光氧化实验和纳秒瞬态吸收光谱的结合，探索芳基三烷基-日耳曼和-硅烷阳离子自由基的裂解反应，来检验这些显著结果的普遍性。此外，将研究Dinnocenzo实验室最近发现的两种新型电荷转移激络合物中间体。一类外杂是由阳离子激发态受体与中性供体反应形成的，这导致了前所未有的发射性阳离子外杂的形成。研究目标包括通过理论拟合复合物的辐射寿命（由时间相关的单光子计数确定）及其荧光光谱来确定复合物（如电子耦合矩阵元素）的电子性质，探索阳离子复合物的普遍性，并测量它们的一些光物理性质。一个相关的项目将调查在PI的实验室中发现的例子，其中观察到来自单个受体和供体的两个异构体发射。初步结果表明，两类异构体的溶剂重组能存在显著差异。拟议的研究将确定杂合体的电子性质并探索其普遍性。

With this award, the Chemical Structure, Dynamics, and Mechanism B Program is supporting Professor Joseph P. Dinnocenzo at the University of Rochester to investigate the selective formation of highly reactive aryl radicals under mild conditions. The mechanistic insight gained from these studies can provide the knowledge necessary to rationally utilize the chemistry in synthesis and in the design of new materials. In addition, research on newly discovered cationic exciplexes and exciplexes that exhibit dual emissions will provide knowledge on these novel excited state intermediates. Research to better understand the fundamental photophysical properties these exciplexes intermediates will provide valuable knowledge for the design of efficient photoinduced electron transfer reactions and for potential use in sensing applications. Student co-workers will learn to carry out chemical syntheis and to conduct mechanistic studies in photochemistry. including a range of less traditional techniques (fluorometry, transient absorption spectroscopy, time-correlated single photon counting, electrochemistry, and modern computational methods). Thus, students trained with NSF support will be well prepared to tackle a variety of multidisciplinary problems in their professional, scientific careers.This project will also benefit undergraduate students through the NSF REU summer program at the University of Rochester with particular attention paid to recruiting students from groups traditionally underrepresented in science and engineering.Recent work in the Dinnocenzo laboratory has revealed that aryltrialkylstannane cation radicals undergo nucleophile-assisted fragmentation reactions in which less stable aryl radicals are often formed in preference to more stable alkyl radicals - an seemingly contrathermodynamic result. This selectivity is unprecedented in ion radical chemistry. Proposed research will test the generality of these remarkable results by exploring the fragmentation reactions of aryltrialkyl-germane and -silane cation radicals through the combined use of synthesis, steady-state photooxidation experiments, and nanosecond transient absorption spectroscopy. In addition, two types of novel, charge-transfer exciplex intermediates recently discovered in the Dinnocenzo laboratory will be investigated. One type of exciplex is formed by reaction of cationic, excited state acceptors with neutral donors, which leads to the formation of emissive cationic exciplexes that are without precedent. Research objectives include determining the electronic nature of the exciplexes (e.g. electronic coupling matrix elements) through theoretical fitting of the radiative lifetimes of the exciplexes (determined by time-correlated single photon counting) and their fluorescence spectra, exploring the generality of cationic exciplexes, and measuring some of their photophysical properties. A related project will investigate examples uncovered in the PI's lab where two exciplex emissions are observed from a single acceptor and donor. Preliminary results indicate dramatically different solvent reorganization energies for the two types of exciplexes. Proposed research will determine the electronic properties of the exciplexes and explore their generality.