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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Excited State Processes of 2-Butylamino-6-methyl-4-nitropyridine N-oxide in Nonpolar Solvents. A Transient Absorption Spectroscopy Study
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Excited State Processes of 2-Butylamino-6-methyl-4-nitropyridine N-oxide in Nonpolar Solvents. A Transient Absorption Spectroscopy Study

机译：非极性溶剂中2-丁基氨基-6-甲基-4-硝基吡啶N-氧化物的激发态过程。瞬态吸收光谱研究

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摘要

Earlier steady-state fluorescence studies showed that 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M) can undergo fast excited-state intramolecular proton transfer (ESIPT). In a nonpolar solvent such as n-octane, both normal and tautomeric fluorescence was observed. Strikingly, the relative ratio of those two emission bands and the fluorescence quantum yield of the normal emission were found to depend on the excitation wavelength in violation of the Kasha-Vavilov rule. In this work, the system was investigated further by means of transient absorption spectroscopy, followed by global and target analysis. Upon excitation at 420 nm, a normal excited singlet state S1(N) is reached, which decays in about 12 ps via fluorescence and ESIPT (minor pathways) and to a long-lived “dark” state (major pathway) that is most probably the triplet T1(N). Upon 330 nm excitation, however, a more complex pattern emerges and additional decay channels are opened. A set of four excited-state species is required to model the data, including a hot state S1(N)* that decays in about 3 ps to the tautomer, to the long-lived “dark” state and to the relaxed S1(N) state. A kinetic scheme is presented that can explain the observed transient absorption results as well as the earlier fluorescence data.
机译：早期的稳态荧光研究表明，2-丁基氨基-6-甲基-4-硝基吡啶N-氧化物（2B6M）可以经历快速激发态的分子内质子转移（ESIPT）。在非极性溶剂（例如正辛烷）中，可以观察到正常和互变异构荧光。令人惊讶的是，发现这两个发射带的相对比率和正常发射的荧光量子产率取决于激发波长，违反了Kasha-Vavilov规则。在这项工作中，通过瞬态吸收光谱法对系统进行了进一步研究，然后进行了全局和目标分析。在420 nm激发后，达到正常的激发单重态S1（N），该状态通过荧光和ESIPT（次要途径）以约12 ps的速率衰减，并变为很可能是长寿命的“暗”状态（主要途径）三元组T1（N）。然而，在330 nm激发下，出现了更复杂的图案，并打开了其他衰减通道。需要一组四个激发态物质来对数据建模，包括热态S1（N）*，它以约3 ps的速率衰减到互变异构体，长寿命的“暗”态和松弛的S1（N） ）状态。提出了一个动力学方案，可以解释观察到的瞬时吸收结果以及较早的荧光数据。

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