Department of Chemistry, Technical University of Munich, D-85747 Garching, Germany.
Institute of Physics, Polish Academy of Sciences, PL-02-668 Warsaw, Poland.
J Phys Chem B. 2022 Apr 21;126(15):2777-2788. doi: 10.1021/acs.jpcb.2c00705. Epub 2022 Apr 6.
In this Perspective, we discuss a novel water-splitting scenario, namely the direct oxidation of water molecules by organic photooxidants in hydrogen-bonded chromophore-water complexes. In comparison with the established scenario of semiconductor-based water splitting, the distance of electron transfer processes is thereby reduced from mesoscopic scales to the Ångström scale, and the time scale is reduced from milliseconds to femtoseconds, which suppresses competing loss processes. The concept is illustrated by computational studies for the heptazine-HO complex. The excited-state landscape of this complex has been characterized with electronic-structure methods and the proton-coupled electron-transfer dynamics has been explored with nonadiabatic dynamics simulations. A unique feature of the heptazine chromophore is the existence of a low-lying and exceptionally long-lived ππ* state in which a substantial part of the photon energy can be stored for hundreds of nanoseconds and is available for the oxidation of water molecules. The calculations reveal that the absorption spectra and the photochemical functionalities of heptazine chromophores can be systematically tailored by chemical substitution. The options of harvesting hydrogen and the problems posed by the high reactivity of OH radicals are discussed.
在这篇观点文章中，我们讨论了一种新颖的水分解方案，即有机光氧化剂在氢键发色团-水分子复合物中直接氧化水分子。与基于半导体的水分解的既定方案相比，电子转移过程的距离从介观尺度减小到埃尺度，时间尺度从毫秒减小到飞秒，从而抑制了竞争的损耗过程。该概念通过对庚嗪-HO 配合物的计算研究得到了说明。用电子结构方法对该配合物的激发态景观进行了表征，并通过非绝热动力学模拟研究了质子耦合电子转移动力学。庚嗪发色团的一个独特特征是存在一个低能且异常长寿命的ππ*态，其中光子能量的很大一部分可以存储数百纳秒，并可用于氧化水分子。计算表明，通过化学取代可以系统地调整庚嗪发色团的吸收光谱和光化学功能。讨论了氢的收集选项以及 OH 自由基的高反应性带来的问题。
