He Yixin, Shangguan Zhichun, Zhang Zhao-Yang, Xie Mingchen, Yu Chunyang, Li Tao
School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Aging, Shanghai Jiao Tong University, Shanghai, 200240, China.
Angew Chem Int Ed Engl. 2021 Jul 19;60(30):16539-16546. doi: 10.1002/anie.202103705. Epub 2021 Jun 17.
Azobenzenes are classical molecular photoswitches that have been widely used. In recent endeavors of molecular design, replacing one or both phenyl rings with heteroaromatic rings has emerged as a strategy to expand molecular diversity and access improved photoswitching properties. Many mono-heteroaryl azo molecules with unique structures and/or properties have been developed, but the potential of bis-heteroaryl architectures is far from fully exploited. We report a family of azobispyrazoles, which combine (near-)quantitative bidirectional photoconversion and widely tunable Z-isomer thermal half-lives from hours to years. The two five-membered rings remarkably weaken the intramolecular steric hindrance, providing new possibilities for engineering the geometric and electronic structure of azo photoswitches. Azobispyrazoles generally exhibit twisted Z-isomers that facilitate complete Z→E photoisomerization, and their thermal stability can be broadly adjusted regardless of the twisted shape, overcoming the conflict between photoconversion (favored by the twisted shape) and Z-isomer stability (favored by the orthogonal shape) encountered by mono-heteroaryl azo switches.
偶氮苯是一类已被广泛应用的经典分子光开关。在最近的分子设计工作中，用杂芳环取代一个或两个苯环已成为一种扩展分子多样性并获得更好光开关性能的策略。许多具有独特结构和/或性质的单杂芳基偶氮分子已被开发出来，但双杂芳基结构的潜力远未得到充分利用。我们报道了一类偶氮双吡唑，它们兼具（近乎）定量的双向光转换以及从数小时到数年广泛可调的Z异构体热半衰期。这两个五元环显著减弱了分子内的空间位阻，为设计偶氮光开关的几何和电子结构提供了新的可能性。偶氮双吡唑通常呈现扭曲的Z异构体，这有利于实现完全的Z→E光异构化，并且无论其扭曲形状如何，它们的热稳定性都能得到广泛调节，克服了单杂芳基偶氮开关所面临的光转换（受扭曲形状青睐）和Z异构体稳定性（受正交形状青睐）之间的矛盾。
