Dispersion-induced structural preference in the ultrafast dynamics of diphenyl ether.
Dispersion-induced structural preference in the ultrafast dynamics of diphenyl ether.
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二苯醚超快动力学中色散诱导的结构偏好
作者：
分散相互作用在大型芳烃体系中无处不在，并作为分子间力影响动力学。利用飞秒时间分辨瞬态吸收（TA）和量子化学计算，研究了二苯醚（DPE）分子的色散相互作用对激发态动力学的影响.在非质子溶剂中的实验结果表明，S1态在267 nm处照射时被填充，多余的振动能量在几皮秒内耗散到溶剂分子中，然后在50 ps内通过内转换（IC）以及系统间交叉（ISC）和荧光衰变，寿命为纳秒。溶剂的极性干扰了激发态能量，提高了ISC通道的能垒。此外，分子间的分散相互作用与质子溶剂导致在甲醇中的OH-π异构体占主导地位，而在叔丁醇中的OH-O异构体略有优势，在基态。氢键异构体的测量表明，除了在非质子溶剂中的弛豫过程之外，在前1 ps中还存在从OH-O到OH-π几何构型的额外变化。在TA光谱中测得的时间常数表明，OH-O异构体促进IC。结果表明，OH-π异构体具有更高的刚性结构和更高的IC势垒，使其更难通过构象重排达到几何圆锥相交。这项工作使我们能够有一个很好的知识，如何分散相互作用诱导的结构偏好影响杂芳族化合物的激发态动力学。
Dispersion interactions are omnipresent in large aromatic systems and influence the dynamics as intermolecular forces. The structural preference induced by dispersion interactions is demonstrated to influence the excited state dynamics of diphenyl ether (DPE) using femtosecond time-resolved transient absorption (TA) associated with quantum chemical calculations. The experimental results in aprotic solvents show that the S1 state is populated upon irradiation at 267 nm with excess vibrational energy dissipating to solvent molecules in several picoseconds, and then decays via internal conversion (IC) within 50 ps as well as intersystem crossing (ISC) and fluorescence with a lifetime of nanoseconds. The polarity of the solvent disturbs the excited state energies and enhances the energy barriers of the ISC channel. Furthermore, the intermolecular dispersion interactions with protic solvents result in the OH–π isomer dominating in methanol and the OH–O isomer is slightly preferred in t-butanol in the ground state. The hydrogen bonded isomer measurements show an additional change from OH–O to OH–π geometry in the first 1 ps besides the relaxation processes in aprotic solvents. The time constants measured in the TA spectra suggest that the OH–O isomer facilitates IC. The results show that the OH–π isomer has a more rigid structure and a higher barrier for IC, making it harder to reach the geometric conical intersection through conformer rearrangement. This work enables us to have a good knowledge of how the structural preference induced by dispersion interactions affects excited state dynamics of the heteroaromatic compounds.
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