We present a conspectus of recent joint spectroscopic and computational studies that provided novel insight into the photochemistry of hydrogen-bonded complexes of the heptazine (Hz) chromophore with hydroxylic substrate molecules (water and phenol). It was found that a functionalized derivative of Hz, tri-anisole-heptazine (TAHz), can photooxidize water and phenol in a homogeneous photochemical reaction. This allows the exploration of the basic mechanisms of the proton-coupled electron-transfer (PCET) process involved in the water photooxidation reaction in well-defined complexes of chemically tunable molecular chromophores with chemically tunable substrate molecules. The unique properties of the excited electronic states of the Hz molecule and derivatives thereof are highlighted. The potential energy landscape relevant for the PCET reaction has been characterized by judicious computational studies. These data provided the basis for the demonstration of rational laser control of PCET reactions in TAHz–phenol complexes by pump–push–probe spectroscopy, which sheds light on the branching mechanisms occurring by the interaction of nonreactive locally excited states of the chromophore with reactive intermolecular charge-transfer states. Extrapolating from these results, we propose a general scenario that unravels the complex photoinduced water-splitting reaction into simple sequential light-driven one-electron redox reactions followed by simple dark radical–radical recombination reactions.

中文翻译：

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基于庚嗪的分子光催化剂对水的光氧化：光谱学和计算化学的见解。

我们提出了最近的联合光谱学和计算研究的概论，这些研究提供了对庚嗪（Hz）生色团与羟基底物分子（水和苯酚）的氢键合配合物的光化学的新见解。已发现，Hz的官能化衍生物三茴香醚庚嗪（TAHz）可以在均相光化学反应中光氧化水和苯酚。这允许探索在化学可调分子生色团与化学可调底物分子的明确定义的复合物中水光氧化反应中涉及的质子耦合电子转移（PCET）过程的基本机理。突出显示了Hz分子及其衍生物的激发电子态的独特性质。与PCET反应有关的势能图已经通过明智的计算研究进行了表征。这些数据为通过泵推-探针光谱论证合理地控制TAHz-苯酚配合物中PCET反应的PCET反应提供了基础，该光谱揭示了生色团的非反应性局部激发态与反应性分子间相互作用引起的支化机理。电荷转移状态。从这些结果推论，我们提出了一个一般情况，将复杂的光致水分解反应分解为简单的顺序光驱动的单电子氧化还原反应，然后进行简单的暗自由基-自由基重组反应。这些数据为通过泵推-探针光谱论证合理地控制TAHz-苯酚配合物中PCET反应的PCET反应提供了基础，该光谱揭示了生色团的非反应性局部激发态与反应性分子间相互作用引起的支化机理。电荷转移状态。从这些结果推论，我们提出了一个一般情况，将复杂的光致水分解反应分解为简单的顺序光驱动的单电子氧化还原反应，然后进行简单的暗自由基-自由基重组反应。这些数据为通过泵推-探针光谱论证合理地控制TAHz-苯酚配合物中PCET反应的PCET反应提供了基础，该光谱揭示了生色团的非反应性局部激发态与反应性分子间相互作用引起的支化机理。电荷转移状态。从这些结果推论，我们提出了一个一般情况，将复杂的光致水分解反应分解为简单的顺序光驱动的单电子氧化还原反应，然后进行简单的暗自由基-自由基重组反应。