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

热、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量转换。PCET的热力学和动力学益处与电荷产生和电荷转移/增加都不影响产物或过渡态的事实相关。一个主要的例子是协同质子电子转移（CPET）。因此，理解PCET和通过支持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的效率至关重要。我们的项目旨在开创性的基础研究，应该揭示压力作为一个重要的物理参数如何可以用作一种工具：（i）评估和区分不同的PCET机制，（ii）了解影响它们的因素，（iii）诱导机械转换，反过来，最大化反应速率。压力对动力学的影响的特征在于活化体积，其对过渡态的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PCs的关键因素。此外，压力调制是一种独特的方式，一方面影响内球（PC）ET中的键断裂/形成和外球（PC）ET中的重组能，另一方面调节远程（PC）ET中的电子-供体受体距离/排列/电子耦合。在这里，在我们的模型研究中，关于一系列新合成的分子系统，基于氧化还原活性金属中心和氢键组装的压力动力学，我们将收集热，电化学和光化学PCO 2的全面理解。为此，最突出的例子是均相与非均相的自交换PCO 2，单向与双向交叉PCO 2，以及共价键或氢键分子组装体及其组合内的PCET过程。通过系统地增加所研究系统的复杂性，我们将能够关联不同但互补的过程之间的影响，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阐明。相应的选择将取决于分子系统，并且范围将从例如吸收、荧光、IR和拉曼到稳态或时间分辨方式中的高压池中的电化学和NMR，由诸如ESI-MS、EPR、X射线等的一般分析技术补充。除了压力变化，温度也将是一个重要的变量，作为协同工具，以证实反应机制和微调反应动力学。

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.