Exploring Arylazo-3,5-Bis(trifluoromethyl)pyrazole Switches

Arylazopyrazoles
stand out among the azoheteroarene photoswitches
due to their excellent properties in terms of stability of the least
stable isomer and conversion between isomers, leading to their use
in several interesting applications. We report herein the synthesis
of arylazo-trifluoromethyl-substituted pyrazoles and their switching
behavior under light irradiation. UV–vis and NMR experiments
showed that arylazo-1H-3,5-bis(trifluoromethyl)pyrazoles
displayed very long half-lives in DMSO (days), along with reasonable
values of other parameters that characterize a photoswitch. Inclusion
of naphthyl moieties as aryl counterparts of the arylazopyrazoles
is beneficial only in combination with trifluoromethyl groups, while
extending the conjugation by grafting the pyrazole moiety with electron-donating
or -withdrawing substituents positively affects the photoswitching
behavior, in terms of isomerization yield and half-lives of the least
stable isomer. The experimental values were correlated with theoretical
calculations indicating the valuable influence of the trifluoromethyl
groups onto the photoswitching behavior.

芳基偶氮吡唑（Arylazopyrazoles）在偶氮杂芳烃光开关（azoheteroarene photoswitches）中脱颖而出，因其在最不稳定异构体的稳定性以及异构体间转化效率方面的优异性能，而被应用于多项颇具价值的研究场景中。本文报道了芳基偶氮-三氟甲基取代吡唑的合成方法，以及其在光辐照下的开关行为。紫外-可见（UV–vis）光谱与核磁共振（NMR）实验结果表明，芳基偶氮-1H-3,5-双（三氟甲基）吡唑在二甲基亚砜（DMSO）溶剂中拥有长达数日的超长半衰期，同时其表征光开关性能的其他参数也处于合理区间。将萘基片段作为芳基偶氮吡唑的芳基取代部分，仅在与三氟甲基基团结合时才具有增益效果；而通过在吡唑环上嫁接给电子或吸电子取代基以拓展共轭体系，则可从异构化产率与最不稳定异构体半衰期两方面，对光开关性能产生积极影响。实验数据与理论计算结果相互印证，表明三氟甲基基团对该类光开关的性能具有关键调控作用。