The development of novel vibrational reporters (VRs), aka infrared (IR) probes, to study local environments and dynamic processes in biomolecules and materials continues to be an important area of research. Azides are important VRs because of their small size and large transition dipole strengths, however, their relatively short vibrational lifetimes (<2 ps) have limited their full potential. Herein we report that the vibrational lifetimes of azides can be increased by attaching them to heavy atoms and by using heavy ¹⁵N isotopes. Three group 14 atom triphenyl azides (Ph₃CN₃, Ph₃SiN₃, Ph₃SnN₃), and their triple-¹⁵N isotopomers, were synthesized in good yields. Tributyltin azide and its heavy isotopomer (Bu₃Sn¹⁵N₃) were also prepared to probe the effect of molecular scaffolding. The extinction coefficients for the natural abundance azides were determined, ranging from 900 to 1500 M⁻¹ cm⁻¹. The vibrational lifetimes of all azides were measured by pump–probe IR spectroscopy and each showed a major component with a short-to-moderate vibrational lifetime and a minor component with a much longer vibrational lifetime. Based on these results, the lifetime, aka the observation window, of an azide reporter can be extended from ∼2 ps to as long as ∼300 ps by a combination of isotopic labeling and heavy atom effect. 2D IR measurements of these compounds further confirmed the ability to observe these azide transitions at much longer timescales showing their utility to capture dynamic processes from tens to hundreds of picoseconds.

中文翻译：

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延长重原子与叠氮化物的振动寿命。

研发新颖的振动报告器（VR），又名红外（IR）探针以研究生物分子和材料中的局部环境以及动态过程，仍然是重要的研究领域。叠氮化物因其体积小和过渡偶极强度大而成为重要的VR，但是其相对较短的振动寿命（<2 ps）限制了其全部潜力。在此我们报告说，通过将叠氮化物附着到重原子上并使用重¹⁵ N同位素，可以提高叠氮化物的振动寿命。三族14原子三苯叠氮化物（Ph ₃ CN ₃，Ph ₃ SiN ₃，Ph ₃ SnN ₃），以及它们的三重¹⁵N异构体以高收率合成。还制备了叠氮化三丁基锡及其重的同位素异构体（Bu ₃ Sn ¹⁵ N ₃），以探讨分子支架的作用。确定了自然丰度叠氮化物的消光系数，范围为900至1500 M ^-1 cm ^-1。所有叠氮化物的振动寿命都通过泵浦探针红外光谱仪进行了测量，每一个都显示出主要成分具有短至中等的振动寿命，次要成分则具有更长的振动寿命。根据这些结果，通过同位素标记和重原子效应的结合，叠氮化物报告分子的寿命（也称为观察窗）可以从约2 ps延长至约300 ps。这些化合物的2D IR测量进一步证实了在更长的时间尺度上观察这些叠氮化物跃迁的能力，表明它们可用于捕获数十皮秒至数百皮秒的动态过程。