School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia.
Department of Chemical Engineering, University of Melbourne, Parkville, Victoria 3010, Australia.
Phys Rev Lett. 2018 Jun 1;120(22):223002. doi: 10.1103/PhysRevLett.120.223002.
The shapes of many molecules can be transformed by light or heat. Here we investigate collision- and photon-induced interconversions of EE, EZ, and ZZ isomers of the isolated Congo red (CR) dianion, a double molecular switch containing two ─N═N─ azo groups, each of which can have the E or Z configuration. We find that collisional activation of CR dianions drives a one-way ZZ→EZ→EE cascade towards the lowest-energy isomer, whereas the absorption of a single photon over the 270-600 nm range can switch either azo group from E to Z or Z to E, driving the CR dianion to lower- or higher-energy forms. The experimental results, which are interpreted with the aid of calculated statistical isomerization rates, indicate that photoisomerization of CR in the gas phase involves a passage through conical intersection seams linking the excited and ground state potential energy surfaces rather than through isomerization on the ground state potential energy surface following internal conversion.
许多分子的形状可以通过光或热来改变。在这里，我们研究了孤立刚果红（CR）二负离子的 EE、EZ 和 ZZ 异构体之间的碰撞和光子诱导的互变，CR 二负离子是一种双分子开关，包含两个 ─N═N─偶氮基团，每个偶氮基团可以具有 E 或 Z 构型。我们发现，CR 二负离子的碰撞激活会驱动 ZZ→EZ→EE 的单向级联，朝着最低能量异构体进行，而在 270-600nm 范围内吸收单个光子可以将任一偶氮基团从 E 变为 Z 或 Z 变为 E，从而使 CR 二负离子向低能或高能形式转变。实验结果通过计算统计异构化速率进行解释，表明气相中 CR 的光致异构化涉及通过连接激发态和基态势能面的锥形交叉缝，而不是通过内部转换后在基态势能面上的异构化。
