Pressure effects on thermal and photochemical proton-coupled electron transfer reactions with metal complexes

压力对金属络合物热和光化学质子耦合电子转移反应的影响

• 批准号: 388524950
• 负责人: Professor Dr. Dirk M. Guldi
• 金额: --
• 依托单位: Lehrstuhl für Physikalische Chemie I
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/388524950?language=en
• 关键词: Pressure; effects; thermal; photochemical; proton

Thermal, electrochemical, and/or photochemical proton-coupled electron transfer (PCET) governs the chemical energy conversion in natural and artificial systems. Thermodynamic and kinetic benefits of PCET correlate with the fact that neither charge generation, nor charge shift/increase impact product or transition state. A leading example is a concerted proton-electron transfer (CPET). As such, understanding PCET and ways to modulate them by favoring CPET rather than stepwise electron (ET) and proton transfer (PT) is of utmost importance toward increasing efficiency of the energy conversion. Our project aims at pioneering fundamental studies that should reveal how pressure as an important physical parameter can be used as a tool to: (i) assess and distinguish between different PCET mechanisms, (ii) understand the factors that affect them, and (iii) induce mechanistic changeovers and, in turn, maximize reaction rates. A pressure effect on kinetics is characterized by a volume of activation, which is highly sensitive to changes in overall charge or intramolecular charge distribution en route to the transition state. Thus, it evolves as a key factor for differentiating and manipulating PCETs. In addition, pressure modulation is a unique way to impact bond breaking / formation in inner-sphere (PC)ET and reorganization energy in outer sphere (PC)ET, on one hand, and to tune electron-donor acceptor distance / alignment/electronic coupling in long-range (PC)ET, on the other hand. Here in our model studies regarding variably pressure kinetics of a series of newly synthesized molecular systems, based on redox-active metal centers and hydrogen bonded assemblies, we will gather a comprehensive understanding of thermal, electrochemical, and photochemical PCETs. To this end, the most prominent examples are homogeneous vs. heterogeneous self-exchange PCETs, uni- vs. bi-directional cross PCETs, as well as PCET processes within covalent or hydrogen bond molecular assemblies and their combinations. By systematically increasing the complexity of the investigated systems, we will be able to correlate the effects between different, but complementary processes such as between inter- and intramolecular reactions or between self exchange and cross PCET reactions. Methodologically, we will use a synergy between syntheses and a variety of experimental techniques for kinetic elucidations. The respective choices will depend on the molecular system and will range from, for example, absorption, fluorescence, IR, and Raman to electrochemistry and NMR in high pressure cells either in a steady-state or in a time-resolved modus, complemented by general analytical techniques such as ESI-MS, EPR, X-ray, etc.. In addition to pressure variation, temperature will also be an important variable both as synergistic tools to corroborate reaction mechanisms and to fine-tune reaction kinetics.

热学、电化学和/或光化学质子耦合电子转移（PCET）控制着自然和人工系统中的化学能转换。PCET的热力学和动力学优势与既不会产生电荷，也不会产生电荷移动/增加影响产物或过渡态这一事实相关。一个主要的例子是协调质子-电子转移（CPET）。因此，了解PCET以及通过支持CPET而不是逐步电子（ET）和质子转移（PT）来调节它们的方法对于提高能量转换效率至关重要。我们的项目旨在开拓基础研究，揭示压力作为一个重要的物理参数如何被用作工具，以：(i)评估和区分不同的PCET机制，（ii）了解影响它们的因素，以及（iii）诱导机制转换，进而最大化反应速率。压力对动力学的影响以活化体积为特征，它对过渡态过程中总电荷或分子内电荷分布的变化高度敏感。因此，它演变为区分和操纵pcet的关键因素。此外，压力调制是影响内球（PC）ET中键断裂/形成和外球（PC）ET中重组能量的独特方法，也是调节远程（PC）ET中电子-供体-受体距离/对准/电子耦合的独特方法。在我们关于一系列新合成的基于氧化还原活性金属中心和氢键组装的分子体系的变压动力学的模型研究中，我们将对热、电化学和光化学pcet有一个全面的了解。为此，最突出的例子是均相与非均相自交换PCET，单向与双向交叉PCET，以及共价键或氢键分子组装及其组合中的PCET过程。通过系统地增加所研究系统的复杂性，我们将能够将不同但互补的过程之间的影响联系起来，例如分子间和分子内反应之间或自交换和交叉PCET反应之间。在方法上，我们将使用合成之间的协同作用和各种实验技术的动力学说明。各自的选择将取决于分子系统，范围从吸收、荧光、红外和拉曼到高压细胞中的电化学和核磁共振，无论是在稳态还是在时间分辨模式下，辅以一般的分析技术，如ESI-MS、EPR、x射线等。除了压力变化之外，温度也是一个重要的变量，既可以作为证实反应机制的协同工具，也可以作为微调反应动力学的工具。