Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science, ETH Zurich , 8092 Zurich, Switzerland.
Environ Sci Technol. 2017 Nov 21;51(22):13151-13160. doi: 10.1021/acs.est.7b03402. Epub 2017 Nov 2.
Excited triplet state chromophoric dissolved organic matter (CDOM*) is a short-lived mixture of excited-state species that plays important roles in aquatic photochemical processes. Unlike the study of the triplet states of well-defined molecules, which are amenable to transient absorbance spectroscopy, the study of CDOM* is hampered by it being a complex mixture and its low average intersystem crossing quantum yield (Φ). This study is an alternative approach to investigating CDOM* using transient absorption laser spectroscopy. The radical cation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), formed through oxidation by CDOM*, was directly observable by transient absorption spectroscopy and was used to probe basic photophysical properties of CDOM*. Quenching and control experiments verified that TMPD was formed from CDOM* under anoxic conditions. Model triplet sensitizers with a wide range of excited triplet state reduction potentials and CDOM oxidized TMPD at near diffusion-controlled rates. This gives support to the idea that a large cross-section of CDOM* moieties are able to oxidize TMPD and that the complex mixture of CDOM* can be simplified to a single signal. Using the TMPD transient, the natural triplet lifetime and Φ for different DOM isolates and natural waters were quantified; values ranged from 12 to 26 μs and 4.1-7.8%, respectively.
激发态三重态发色溶解有机质（CDOM*）是一种短寿命的激发态物种混合物，在水生光化学过程中起着重要作用。与研究易于通过瞬态吸收光谱研究的明确分子的三重态不同，CDOM的研究受到其复杂混合物和低平均系间穿越量子产率（Φ）的阻碍。本研究是使用瞬态吸收激光光谱研究 CDOM的一种替代方法。通过 CDOM氧化形成的 N，N，N'，N'-四甲基-p-苯二胺（TMPD）的自由基阳离子可通过瞬态吸收光谱直接观察，并用于探测 CDOM的基本光物理性质。猝灭和对照实验证实，在缺氧条件下 TMPD 是从 CDOM形成的。具有广泛激发三重态还原电势的模型三重态敏化剂和 CDOM 以接近扩散控制的速率氧化 TMPD。这支持了这样一种观点，即 CDOM的很大一部分能够氧化 TMPD，并且 CDOM*的复杂混合物可以简化为单个信号。使用 TMPD 瞬变，量化了不同 DOM 分离物和天然水的自然三重态寿命和Φ；值范围从 12 到 26 μs 和 4.1-7.8%，分别。
