He Yixin, Dang Tongtong, Leach Andrew G, Zhang Zhao-Yang, 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.
Division of Pharmacy and Optometry, School of Health Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, U.K.
J Am Chem Soc. 2024 Oct 23;146(42):29237-29244. doi: 10.1021/jacs.4c12532. Epub 2024 Oct 14.
Azo molecules, being extensively studied as photoswitches, have demonstrated versatile photoswitching performance and applications in solution-phase systems. However, the dense molecular packing and insufficient conformational freedom in the solid/crystalline state typically pose a challenge to their ⇆ isomerization. This study presents a breakthrough in solid-state azo chemistry, where the investigated azobispyrazole molecules are capable of achieving high → photoconversion, ranging from 85% to nearly quantitative (96%), and quantitative → photoswitching in their crystalline states. To the best of our knowledge, azobispyrazoles are the first photoswitchable azo crystals that achieve high-yield bidirectional conversions, particularly the challenging thermodynamically stable-to-metastable → transformation. Crystallographic and computational analyses provide in-depth insights into the photoswitching mechanism and propose that locally distributed free spaces and weak intermolecular interactions within the crystal structures are key factors contributing to the crystalline-state conversion. This work opens up new avenues for the development of promising photoswitchable azo crystals and also underscores the potential application of azobispyrazole crystals as light-responsive materials.
偶氮分子作为光开关受到广泛研究，已在溶液相体系中展现出多样的光开关性能及应用。然而，在固态/结晶态下，分子的密集堆积以及构象自由度不足通常对其 ⇆ 异构化构成挑战。本研究在固态偶氮化学领域取得了一项突破，所研究的偶氮双吡唑分子在其结晶态下能够实现高达85%至近乎定量（96%）的高 → 光转化，以及定量的 → 光开关切换。据我们所知，偶氮双吡唑是首批实现高产率双向转化的可光开关偶氮晶体，尤其是具有挑战性的从热力学稳定态到亚稳态的 → 转变。晶体学和计算分析为光开关机制提供了深入见解，并提出晶体结构内局部分布的自由空间和弱分子间相互作用是促成结晶态转化的关键因素。这项工作为开发有前景的可光开关偶氮晶体开辟了新途径，也凸显了偶氮双吡唑晶体作为光响应材料的潜在应用。
