Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
Department of Chemistry, University of Nevada at Reno, Reno, NV 89557, USA.
Phys Chem Chem Phys. 2020 Aug 24;22(32):18007-18013. doi: 10.1039/d0cp02814b.
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.
新型振动报告器（VRs），又名红外（IR）探针，用于研究生物分子和材料中的局部环境和动态过程，这一领域的研究仍在继续。由于叠氮化物尺寸小、跃迁偶极矩强度大，因此它们是重要的 VRs，但其相对较短的振动寿命（<2 ps）限制了它们的全部潜力。在此，我们报告说，通过将叠氮化物连接到重原子上并使用重 15N 同位素，可以增加它们的振动寿命。我们合成了三个第 14 族原子三苯基叠氮化物（Ph3CN3、Ph3SiN3、Ph3SnN3）及其三重 15N 同位素物，产率均较高。还制备了三丁基锡叠氮化物及其重同位素物（Bu3Sn15N3）以探究分子支架的影响。测定了天然丰度叠氮化物的消光系数，范围在 900 至 1500 M-1 cm-1。通过泵浦-探测 IR 光谱法测量了所有叠氮化物的振动寿命，每种叠氮化物都显示出一个具有短至中等振动寿命的主要组分和一个具有更长振动寿命的次要组分。基于这些结果，通过同位素标记和重原子效应的组合，可以将叠氮化物报告器的寿命，即观察窗口，从大约 2 ps 延长到长达大约 300 ps。对这些化合物进行二维 IR 测量进一步证实了可以在更长的时间尺度上观察到这些叠氮化物跃迁的能力，表明它们可以用于捕获从几十到几百皮秒的动态过程。
