Ultrafast Dynamics of Encapsulated Molecules Reveals New Insight on the Photoisomerization Mechanism for Azobenzenes
Ultrafast Dynamics of Encapsulated Molecules Reveals New Insight on the Photoisomerization Mechanism for Azobenzenes
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DOI：
10.1021/acs.jpclett.8b03070
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发表时间：
2019-01-03
影响因子：
5.7
通讯作者：
Elles, Christopher G.
中科院分区：
文献类型：
--
作者：
Otolski, Christopher J.;Raj, A. Mohan;Elles, Christopher G.
空间限制可以对化学反应的动力学产生深远的影响，尤其是对于涉及分子的大振幅结构重排的异构反应。这项工作使用超快光谱法来探测限制对pi pi pi*激发4-丙泊苯乙烯和4-丙基偶氮苯在超分子宿主 - 宿主 - 周期复合物中的激发后的反式 - > cis光异构化的影响。封装的偶氮苯衍生物的瞬时吸收光谱揭示了具有类似于顺式和反式异构体的光谱特征的两个不同激发态物质的形成。顺式物种的形成表明在环己烷溶液中未观察到的直接激发态异构化通道。与Stilbene类似物的比较表明，封装偶氮苯的这种“热”激发态异构化途径主要涉及平面内反转，而跨性别异构体激发态寿命增加了10倍，表明capsule capsule Hinders Hinders Hinders Isomerization s the the Transed s-1 trans issomememerize the Trans issomemerize the isomemerization croped scrodement。这项工作为反转和旋转在偶氮苯衍生物的超快光异构化中的相对作用提供了新的机械见解。
Spatial confinement can have a profound impact on the dynamics of chemical reactions, especially for isomerization reactions that involve large-amplitude structural rearrangement of a molecule. This work uses ultrafast spectroscopy to probe the effects of confinement on trans -> cis photoisomerization following pi pi* excitation of 4-propyl stilbene and 4-propyl azobenzene encapsulated in a supramolecular host-guest complex. Transient absorption spectroscopy of the encapsulated azobenzene derivative reveals the formation of two distinct excited-state species with spectral signatures resembling the cis and trans isomers. Formation of the cis species indicates a direct excited-state isomerization channel that is not observed in cyclohexane solution. Comparison with the stilbene analogue suggests that this "hot" excited-state isomerization pathway for encapsulated azobenzene involves primarily in-plane inversion, whereas a 10-fold increase of the excited-state lifetime for the trans isomer suggests that crowding in the capsule hinders isomerization from the relaxed S-1 geometry of the trans isomer. This work provides new mechanistic insight on the relative roles of inversion and rotation in the ultrafast photoisomerization of azobenzene derivatives.