The lack of general spectroscopic probes that can be used in a range of systems to probe kinetics and dynamics is a major obstacle to the widespread application of two-dimensional infrared (2D IR) spectroscopy. We have studied 3-azidopyridine to characterize its potential as a probe of the protonation state of the pyridine ring. We find that the azido-stretching vibration is split by accidental Fermi resonance interactions with one or more overtones and combination states. Using 2D IR spectroscopy, we determine the state structure of the resulting eigenstates for complexes of 3-azidopyridine with formic acid and trifluoroacetic acid in which the pyridine ring is unprotonated and protonated, respectively. Based on the measurements, we develop a two-oscillator depurturbation model to determine the energies and couplings of the zeroth-order azido-stretching state and the perturbing dark state that couples to it. Based on these results, we conclude that the azido-stretching vibration is, in fact, sensitive to the protonation state of the pyridine shifting up in frequency by 8 cm(-1) in the complex with trifluoroacetic acid relative to the formic acid complex. These results suggest that, although 3-azidopyridine is not suitable as a spectroscopic probe, the approach of employing an organic azide as a remote probe of protonation state holds significant promise.

中文翻译：

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二维红外研究3-叠氮吡啶作为质子化状态的潜在光谱报告者。

缺乏可在一系列系统中用来探测动力学和动力学的通用光谱探针，这是二维红外（2D IR）光谱技术广泛应用的主要障碍。我们已经研究了3-叠氮基吡啶，以表征其作为吡啶环质子化状态探针的潜力。我们发现叠氮延展振动被具有一个或多个泛音和组合状态的偶然费米共振相互作用所分裂。使用二维红外光谱，我们确定了3-叠氮吡啶与甲酸和三氟乙酸配合物的合成本征态的状态结构，其中吡啶环分别为未质子化和质子化。根据测量结果，我们开发了一个两振子去激励模型，以确定零阶叠氮拉伸状态和与其耦合的扰动暗态的能量和耦合。基于这些结果，我们得出结论，叠氮基拉伸振动实际上对吡啶的质子态敏感，该吡啶的质子态在三氟乙酸配合物中相对于甲酸配合物的频率上移了8 cm（-1）。这些结果表明，尽管3-叠氮基吡啶不适合用作光谱探针，但采用有机叠氮化物作为质子化状态的远程探针的方法具有重大前景。对吡啶的质子化状态敏感的频率相对于甲酸络合物与三氟乙酸络合物频率上移了8 cm（-1）。这些结果表明，尽管3-叠氮基吡啶不适合用作光谱探针，但采用有机叠氮化物作为质子化状态的远程探针的方法具有重大前景。对吡啶的质子化状态敏感的频率相对于甲酸络合物与三氟乙酸络合物频率上移了8 cm（-1）。这些结果表明，尽管3-叠氮基吡啶不适合用作光谱探针，但采用有机叠氮化物作为质子化状态的远程探针的方法具有重大前景。