Origins of the diffuse shared proton vibrational signatures in proton-coupled electron transfer model dyad complexes
Origins of the diffuse shared proton vibrational signatures in proton-coupled electron transfer model dyad complexes
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DOI：
10.1063/5.0122777
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发表时间：
2022-10-21
影响因子：
4.4
通讯作者：
Fournier, Joseph A.
中科院分区：
文献类型：
--
作者：
Chen, Liangyi;Ma, Zifan;Fournier, Joseph A.
苯酚-苯并咪唑和苯酚-吡啶二元复合物已成为溶液相实验中质子耦合电子转移（PCET）动力学研究的流行模型系统。然而，根据关键结构参数（例如氢键供体-受体距离）来解释测得的 PCET 速率仍然具有挑战性。在此，我们报告了一系列在离子阱中分离和低温冷却的苯酚-苯并咪唑和苯酚-吡啶配合物的电子基态振动光谱。研究的四个模型均显示出高度红移和加宽的 OH 伸缩转变，这是由苯酚 OH 基团与苯并咪唑/吡啶环上的碱性 N 位点之间的强氢键相互作用引起的。每个模型中的 OH 拉伸转变在 2500 cm(-1) 附近显示出相对较强的吸收起始点，具有宽肩，不对称地延伸到数百个波数的更高频率。相比之下，氘化同位素异数体产生更弱的 OD 拉伸跃迁，表现为对称加宽。 OD 拉伸跃迁的光谱宽度和形状归因于质子供体-受体低频软模式振动中的零点分布引起的 OD 拉伸频率的变化。 OH 拉伸跃迁的不对称结构归因于 OH 拉伸和一系列低频氢键软模式之间的一组组合能带。光谱和建模强调了 OH 拉伸-软模式耦合的重要性，该耦合被认为在 PCET 和质子传输动力学中发挥着重要作用。
Phenol-benzimidazole and phenol-pyridine dyad complexes have served as popular model systems for the study of proton-coupled electron transfer (PCET) kinetics in solution-phase experiments. Interpretation of measured PCET rates in terms of key structural parameters, such as the H-bond donor-acceptor distance, however, remains challenging. Herein, we report vibrational spectra in the electronic ground state for a series of phenol-benzimidazole and phenol-pyridine complexes isolated and cryogenically cooled in an ion trap. The four models studied each display highly red-shifted and broadened OH stretching transitions that arise from strong H-bonding interactions between the phenol OH group and the basic N site on benzimidazole/pyridine rings. The OH stretch transition in each model displays relatively strong absorption onsets near 2500 cm(-1) with broad shoulders that extend asymmetrically to higher frequencies over hundreds of wavenumbers. In contrast, the deuterated isotopologues yield much weaker OD stretch transitions that appear symmetrically broadened. The spectral breadth and shape of the OD stretch transitions are ascribed to variations in OD stretch frequencies that arise from zero-point distributions in the proton donor-acceptor low-frequency soft mode vibration. The asymmetric structure of the OH stretch transitions is attributed to a set of combination bands between the OH stretch and a series of low-frequency H-bond soft modes. The spectra and modeling highlight the importance of OH stretch-soft mode couplings, which are thought to play important roles in PCET and proton transfer dynamics.