Vela Sergi, Scheidegger Alan, Fabregat Raimon, Corminboeuf Clémence
Institute of Chemical Sciences and Engineering, Laboratory for Computational Molecular Design, École Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland.
Chemistry. 2021 Jan 4;27(1):419-426. doi: 10.1002/chem.202003926. Epub 2020 Nov 26.
Azobenzene and its derivatives are one of the most widespread molecular scaffolds used in a range of modern applications, as well as in fundamental research. After photoexcitation, azo-based photoswitches revert back to the most stable isomer on a timescale ( ) that determines the range of potential applications. Attempts to bring to extreme values prompted the development of azobenzene and azoheteroarene derivatives that either rebalance the E- and Z-isomer stabilities, or exploit unconventional thermal isomerization mechanisms. In the former case, one successful strategy has been the creation of macrocycle strain, which tends to impact the E/Z stability asymmetrically, and thus significantly modify . On the bright side, bridged derivatives have shown an improved optical switching owing to the higher quantum yields and absence of degradation. However, in most (if not all) cases, bridged derivatives display a reversed thermal stability (more stable Z-isomer), and smaller than the acyclic counterparts, which restricts their potential interest to applications requiring a fast forward and backwards switch. In this paper, the impact of alkyl bridges on the thermal stability of phenyl-azoheteroarenes is investigated by using computational methods, and it is revealed that it is indeed possible to combine such improved photoswitching characteristics while preserving the regular thermal stability (more stable E-isomer), and increased values under the appropriate connectivity and bridge length.
偶氮苯及其衍生物是一系列现代应用以及基础研究中使用最广泛的分子骨架之一。光激发后，基于偶氮的光开关会在一个决定潜在应用范围的时间尺度（ ）上恢复到最稳定的异构体。将 推向极值的尝试促使了偶氮苯和偶氮杂芳烃衍生物的发展，这些衍生物要么重新平衡E-异构体和Z-异构体的稳定性，要么利用非常规的热异构化机制。在前一种情况下，一种成功的策略是产生大环张力，这往往会不对称地影响E/Z稳定性，从而显著改变 。从好的方面来看，桥连衍生物由于具有更高的量子产率和不存在降解而表现出改进的光开关性能。然而，在大多数（如果不是全部）情况下，桥连衍生物表现出相反的热稳定性（Z-异构体更稳定），并且 比非环状对应物小，这限制了它们在需要快速正向和反向切换的应用中的潜在应用价值。在本文中，通过使用计算方法研究了烷基桥对苯基-偶氮杂芳烃热稳定性的影响，结果表明，在适当的连接性和桥长度下，确实有可能在保持常规热稳定性（E-异构体更稳定）的同时，结合这种改进的光开关特性，并提高 值。
