Unraveling the Vibrational Spectral Signatures of a Dislocated H Atom in Model Proton-Coupled Electron Transfer Dyad Systems
Unraveling the Vibrational Spectral Signatures of a Dislocated H Atom in Model Proton-Coupled Electron Transfer Dyad Systems
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揭示质子耦合电子转移二元系统模型中位错氢原子的振动光谱特征
DOI：
10.1021/acs.jpca.3c00524
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Fournier, Joseph A.
中科院分区：
文献类型：
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作者：
Chen, Liangyi;Sibert, Edwin L.;Fournier, Joseph A.
对苯酚-苯并咪唑和苯酚-吡啶质子耦合电子转移(PCET)二元体系进行了计算研究，以解决先前用低温离子振动光谱在基电子态上报道的非对称加宽氢键氢键伸缩跃迁的起源。预测了描述强共享H原子的二维势沿H原子转移坐标很浅，使得H原子在激发OH振动模时在施主和受主之间发生位错。这些软H原子势导致了具有显著弯曲-拉伸混合的OH模与大量简正模坐标之间的强耦合。振动光谱的计算使用哈密顿量，它线性和二次耦合H原子势与在谐和水平下处理的20多个最强耦合的简正模。计算的振动光谱定性地再现了在2300-3000 cm-1范围内实验观察到的谱带的不对称形状和宽度。有趣的是，这些转变远远超过了预测的OH伸展基本面，这是计算出令人惊讶的红移(<；2000厘米-1)。与时间相关的计算预测了激发的OH模的快速(<；100fS)弛豫和低频简正模的瞬时响应，证实了模型哈密顿量所预测的强耦合。这些结果突出了在这些生物相关的PCET模型系统中存在的独特的展宽机制和复杂的非谐效应。
Phenol–benzimidazole and phenol–pyridine proton-coupled electron transfer (PCET) dyad systems are computationally investigated to resolve the origins of the asymmetrically broadened H-bonded OH stretch transitions that have been previously reported using cryogenic ion vibrational spectroscopy in the ground electronic state. Two-dimensional (2D) potentials describing the strongly shared H atom are predicted to be very shallow along the H atom transfer coordinate, enabling dislocation of the H atom between the donor and acceptor groups upon excitation of the OH vibrational modes. These soft H atom potentials result in strong coupling between the OH modes, which exhibit significant bend-stretch mixing, and a large number of normal mode coordinates. Vibrational spectra are calculated using a Hamiltonian that linearly and quadratically couples the H atom potentials to over two dozen of the most strongly coupled normal modes treated at the harmonic level. The calculated vibrational spectra qualitatively reproduce the asymmetric shape and breadth of the experimentally observed bands in the 2300–3000 cm–1range. Interestingly, these transitions fall well above the predicted OH stretch fundamentals, which are computed to be surprisingly red-shifted (<2000 cm–1). Time-dependent calculations predict rapid (<100 fs) relaxation of the excited OH modes and instant response from the lower-frequency normal modes, corroborating the strong coupling predicted by the model Hamiltonian. The results highlight a unique broadening mechanism and complicated anharmonic effects present within these biologically relevant PCET model systems.