Excitonic Splitting and Vibronic Coupling Analysis of the m-Cyanophenol Dimer.
Excitonic Splitting and Vibronic Coupling Analysis of the m-Cyanophenol Dimer.
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DOI：
10.1021/acs.jpca.6b10416
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发表时间：
2017-01
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影响因子：
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通讯作者：
Franziska A Balmer;Sabine Kopec;H. Köppel;S. Leutwyler
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作者：
Franziska A Balmer;Sabine Kopec;H. Köppel;S. Leutwyler
利用质量选择双色共振双光子电离和分散荧光光谱研究了间氰酚二聚体（mCP）2的S1/S2分裂及其激态耦合S1/S2态的离域，并基于相关的初始计算在近似耦合簇CC2和SCS-CC2水平上进行了理论振动耦合分析。计算预测了（mCP）2的三个接近的基态极小值：最小的为微z形（ci对称）；第二低为<5 cm-1高且平面（C2h）。振动基态可能在两个极小值上都是离域的。（mCP）2的S0→S1跃迁是电偶极允许的（Ag→Au），而S0→S2跃迁是禁止的（Ag→Ag）。通过12C/13C-或H/ d -取代打破反转对称性，使得S0→S2跃迁部分被允许；激子对S1/S2分裂的贡献为Δexc = 7.3 cm-1。在电子激发下，间氰酚零点振动能的变化为Δiso(12C/13C) = 3.3 cm-1， Δiso(H/D) = 6.8 cm-1。在12C/13C和H/D取代的异源二聚体中，激子只发生部分定位。SCS-CC2计算的激子分裂为Δel = 179 cm-1；将其乘以振动猝灭因子Γvibronexp = 0.043，得到激子分裂Δvibronexp = 7.7 cm-1，与实验结果Δexc = 7.3 cm-1非常吻合。半经典激子跳变时间范围从（mCP）2中的3.2 ps到异源二聚体（mCP-h）·（mCP-d）中的5.7 ps。对从v = 0到600 cm-1以上的耦合S1/S2态的所有振动能级进行了多模振动耦合分析。研究了线性和二次振动耦合方案，模拟了S0→S1/S2的振动谱；后一种方案的计算结果与实验结果吻合较好。
The S1/S2 splitting of the m-cyanophenol dimer, (mCP)2 and the delocalization of its excitonically coupled S1/S2 states are investigated by mass-selective two-color resonant two-photon ionization and dispersed fluorescence spectroscopy, complemented by a theoretical vibronic coupling analysis based on correlated ab initio calculations at the approximate coupled cluster CC2 and SCS-CC2 levels. The calculations predict three close-lying ground-state minima of (mCP)2: The lowest is slightly Z-shaped (Ci-symmetric); the second-lowest is <5 cm-1 higher and planar (C2h). The vibrational ground state is probably delocalized over both minima. The S0 → S1 transition of (mCP)2 is electric-dipole allowed (Ag → Au), while the S0 → S2 transition is forbidden (Ag → Ag). Breaking the inversion symmetry by 12C/13C- or H/D-substitution renders the S0 → S2 transition partially allowed; the excitonic contribution to the S1/S2 splitting is Δexc = 7.3 cm-1. Additional isotope-dependent contributions arise from the changes of the m-cyanophenol zero-point vibrational energy upon electronic excitation, which are Δiso(12C/13C) = 3.3 cm-1 and Δiso(H/D) = 6.8 cm-1. Only partial localization of the exciton occurs in the 12C/13C and H/D substituted heterodimers. The SCS-CC2 calculated excitonic splitting is Δel = 179 cm-1; when multiplying this with the vibronic quenching factor Γvibronexp = 0.043, we obtain an exciton splitting Δvibronexp = 7.7 cm-1, which agrees very well with the experimental Δexc = 7.3 cm-1. The semiclassical exciton hopping times range from 3.2 ps in (mCP)2 to 5.7 ps in the heterodimer (mCP-h)·(mCP-d). A multimode vibronic coupling analysis is performed encompassing all the vibronic levels of the coupled S1/S2 states from the v = 0 level to 600 cm-1 above. Both linear and quadratic vibronic coupling schemes were investigated to simulate the S0 → S1/S2 vibronic spectra; those calculated with the latter scheme agree better with experiment.