Imidazole and 1-Methylimidazole Hydrogen Bonding and Nonhydrogen Bonding Liquid Dynamics: Ultrafast IR Experiments
Imidazole and 1-Methylimidazole Hydrogen Bonding and Nonhydrogen Bonding Liquid Dynamics: Ultrafast IR Experiments
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咪唑和 1-甲基咪唑氢键和非氢键液体动力学：超快红外实验
DOI：
10.1021/acs.jpcb.8b11299
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Fayer, Michael D.
中科院分区：
文献类型：
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作者：
Shin, Jae Yoon;Wang, Yong-Lei;Yamada, Steven A.;Hung, Samantha T.;Fayer, Michael D.
用红外光谱、偏振选择性泵浦探测和二维红外光谱研究了95℃时咪唑(IM)和1-甲基咪唑(1-MeIM)在液相中的动力学。这两个分子在结构上非常相似，除了IM可以同时作为氢键供体和受体，从而形成扩展的氢键网络。IM VS 1-MEIM中振动探针SECN-的红外吸收光谱较宽，振动寿命较短，说明SECN-与IM之间存在较强的氢键作用。分子动力学(MD)模拟支持SECN-与IM之间通过HN部分形成强氢键。SECN-与IM形成两个氢键；它插入IM的H键链中，而不是链的终止符。强烈的氢键影响了SECN-In IM的重取向动力学，导致了更受限制的短时角度采样(锥内摆动)。IM的完全定向扩散时间比1-MeIM慢1.7倍，但考虑到IM的粘度比1-MeIM大3倍，这种减慢比预期的要小。跃迁重定向机制解释了IM中异常快速的取向弛豫，MD模拟确定了探针在氢键位置之间的平均跳跃角。从2D IR实验中获得的光谱扩散时间常数在IM中仅略慢于1-MEIM，尽管粘度显着增加。结果表明，SECN-检测到的光谱扩散具有1-MeIM所没有的IM氢键动力学贡献。
The dynamics of imidazole (IM) and 1-methylimidazole (1-MeIM) in the liquid phase at 95 °C were studied by IR polarization selective pump–probe and two-dimensional IR (2D IR) spectroscopies. The two molecules are very similar structurally except that IM can be simultaneously a hydrogen bond donor and acceptor and therefore forms extended hydrogen-bonded networks. The broader IR absorption spectrum and a shorter vibrational lifetime of the vibrational probe, selenocyanate anion (SeCN–), in IM vs 1-MeIM indicate that stronger hydrogen bonding exists between SeCN–and IM. Molecular dynamics (MD) simulations support the strong hydrogen bond formation between SeCN–and IM via the HN moiety. SeCN–makes two H-bonds with IM; it is inserted in the IM H-bonded chains rather than being a chain terminator. The strong hydrogen bonding influenced the reorientation dynamics of SeCN–in IM, leading to a more restricted short time angular sampling (wobbling-in-a-cone). The complete orientational diffusion time in IM is 1.7 times slower than in 1-MeIM, but the slow down is less than expected, considering the 3-fold larger viscosity of IM. The jump reorientation mechanism accounts for the anomalously fast orientational relaxation in IM, and the MD simulations determined the average jump angle of the probe between hydrogen bonding sites. Spectral diffusion time constants obtained from the 2D IR experiments are only modestly slower in IM than in 1-MeIM in spite of the significant increase in viscosity. The results indicate that the spectral diffusion sensed by the SeCN–has IM hydrogen bond dynamics contributions not present in 1-MeIM.