Zhang Linqi, Wang Chong, Bao Jiming, Kalkan A Kaan
Functional Nanomaterials Laboratory, Oklahoma State University, Stillwater, OK, 74078, USA.
Department of Electrical & Computer Engineering, University of Houston, Houston, TX, 77204, USA.
Commun Chem. 2020 Jun 4;3(1):71. doi: 10.1038/s42004-020-0318-x.
C is regarded as the most efficient singlet oxygen (O) photosensitizer. Yet, its oxidation by self-sensitized O remains unclear. The literature hints both oxygen and C must be at excited states to react, implying a two-photon process: first, oxygen is photosensitized (C•O); second, C is photoexcited ([Formula: see text]•O). However, this scheme is not plausible in a solvent, which would quench O rapidly before the second photon is absorbed. Here, we uncover a single-photon oxidation mechanism via self-sensitized O in solvents above an excitation energy of 3.7 eV. Using excitation spectroscopies and kinetics analysis, we deduce photoexcitation of a higher energy transient, [Formula: see text]•O, converting to [Formula: see text]•O. Such triplet-triplet annihilation, yielding two simultaneously-excited singlets, is unique. Additionally, rate constants derived from this study allow us to predict a C half-life of about a minute in the atmosphere, possibly explaining the scarceness of C in the environment.
C被认为是最有效的单线态氧（O）光敏剂。然而，其被自身敏化产生的O氧化的过程仍不清楚。文献表明氧和C都必须处于激发态才能发生反应，这意味着是一个双光子过程：首先，氧被光敏化（C•O）；其次，C被光激发（[公式：见原文]•O）。然而，在溶剂中这种机制不太合理，因为在吸收第二个光子之前溶剂会迅速淬灭O。在此，我们发现了在激发能高于3.7 eV的溶剂中通过自身敏化产生的O进行单光子氧化的机制。利用激发光谱和动力学分析，我们推断出一种更高能量的瞬态[公式：见原文]•O的光激发，它会转化为[公式：见原文]•O。这种产生两个同时激发的单线态的三重态 - 三重态湮灭是独特的。此外，从这项研究中得出的速率常数使我们能够预测C在大气中的半衰期约为一分钟，这可能解释了环境中C稀缺的原因。
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