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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Inhibition of light-induced tautomerization of 7-azaindole by phenol: Indications of proton-coupled electron/energy transfer quenching
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Inhibition of light-induced tautomerization of 7-azaindole by phenol: Indications of proton-coupled electron/energy transfer quenching

机译：苯酚对光诱导的7-氮杂吲哚互变异构的抑制作用：质子偶联电子/能量转移猝灭的指示

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摘要

The photophysical behavior of a 1:1 complex between phenol and7-azaindole (7AI) has been investigated in methylcyclohexane solutions at temperatures in the range of 27 to -50 °C. A linear Benesi-Hildebrand plot associated with changes in absorbance of the complex with phenol concentration in the solutions ensures 1:1 stoichiometry of the produced complex. Our estimate for the value of the association constant (K_a) of the complex is ～120 M ~(-1) at 27 °C, and it is nearly twice compared to that for 1:1 complex between 7AI and ethanol measured under the same condition. The complexation results in dramatic quenching of the normal fluorescence of 7AI and the process is accelerated upon lowering of temperature. The measured spectra show no indication that phenol promotes tautomerization of 7AI in the excited state. We have argued that the hydrogen bonding between pyridinic N and phenolic O-H (N???O-H) is a vital structural factor responsible for quenching of 7AI fluorescence, and this idea has been corroborated by showing that under same condition the fluorescence of 7AI is enhanced in the presence of anisole. As a plausible mechanism of quenching, we have invoked a proton-coupled electron transfer (PCET) process between phenol and excited 7AI, which outweighs the competing tautomerization process. An analysis in terms of Remm-Weller model reveals that the PCET process involving phenol and excited 7AI could be energetically favorable (ΔGET0 < 0). An alternative mechanism, where quenching can occur via electronic energy transfer from the excited protonated 7AI to phenoxide ion, following a proton transfer along the N???O-H hydrogen bond, is also discussed.
机译：在27至-50°C的温度下，已在甲基环己烷溶液中研究了苯酚与7-氮杂吲哚（7AI）之间1：1配合物的光物理行为。线性的Benesi-Hildebrand图与溶液中酚浓度的配合物吸光度变化相关，可确保所产生配合物的化学计量比为1：1。我们在27°C下对配合物的缔合常数（K_a）的估计值为〜120 M〜（-1），与在相同条件下测得的7AI和乙醇之间1：1配合物的缔合常数相比，几乎是原来的两倍健康）状况。络合导致7AI正常荧光的急剧淬灭，并且温度降低会加速该过程。测量的光谱没有显示苯酚在激发态下促进7AI的互变异构。我们认为，吡啶二氮和酚羟基（N OH）之间的氢键是引起7AI荧光猝灭的重要结构因素，这一想法已得到证实，表明在相同条件下7AI的荧光增强了。在苯甲醚的存在下。作为一种可能的淬灭机理，我们在苯酚和激发的7AI之间引入了质子偶联电子转移（PCET）过程，该过程超过了竞争性互变异构过程。根据Remm-Weller模型进行的分析表明，涉及酚和激发7AI的PCET过程可能在能量上有利（ΔGET0<0）。还讨论了另一种机理，其中在沿着N-O-H氢键的质子转移之后，通过电子能量从激发的质子化的7AI转移到酚盐离子而发生淬灭。

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