Sacherer Maximilian, Gracheva Sofia, Maid Harald, Placht Christian, Hampel Frank, Dube Henry
Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Chemistry and Pharmacy, Nikolaus-Fiebiger-Str. 10, Erlangen 91058, Germany.
J Am Chem Soc. 2024 Apr 10;146(14):9575-9582. doi: 10.1021/jacs.3c11803. Epub 2024 Mar 27.
Diarylethenes belong to the most eminent photoswitches and have been studied for many decades. They are found in virtually every field of application and have become highly valuable molecular tools for instilling light-responsiveness into materials, catalysts, biological systems, or pharmacology. In this work, we present a novel and distinct type of pyrimidine-based aza-diarylethene, which undergoes a highly unusual zwitterion-forming photoreaction. During this fully reversible process, a CN double bond is established under concomitant aromatization and thiophene-ring opening. The metastable zwitterion thus possesses a positively charged extended aromatic structure and an independent conjugated thiolate function. It can further photoisomerize between a more stable and a less stable isomer, resulting in effective four-state photoswitching. Unusual for diarylethenes, the metastable isomers show negative solvatochromism and red-shifted absorption in apolar solvents. With this behavior, aza-diarylethenes effectively bridge the properties of merocyanines and diarylethenes. Thermal stability of the zwitterions can be modulated from very labile to highly stable behavior in response to pH, again in a fully reversible manner. Pyrimidine-based aza-diarylethene thus establishes a unique photoreaction mechanism for diarylethenes, allowing control of charge separation, thermal stability, and color generation in a different way than hitherto possible.
二芳基乙烯属于最杰出的光开关，已经被研究了数十年。它们几乎出现在每一个应用领域，并且已经成为将光响应性引入材料、催化剂、生物系统或药理学中的极具价值的分子工具。在这项工作中，我们展示了一种新型且独特的基于嘧啶的氮杂二芳基乙烯，它经历了一种非常不寻常的形成两性离子的光化学反应。在这个完全可逆的过程中，一个碳氮双键在伴随芳构化和噻吩环开环的情况下形成。由此产生的亚稳态两性离子具有带正电荷的扩展芳香结构和独立的共轭硫醇盐官能团。它可以进一步在更稳定和较不稳定的异构体之间进行光异构化，从而实现有效的四态光开关功能。与二芳基乙烯不同的是，亚稳态异构体在非极性溶剂中表现出负溶剂化显色作用和红移吸收。通过这种行为，氮杂二芳基乙烯有效地桥接了部花青和二芳基乙烯的性质。两性离子的热稳定性可以根据pH值从非常不稳定调节到高度稳定的状态，同样也是以完全可逆的方式。基于嘧啶的氮杂二芳基乙烯因此为二芳基乙烯建立了一种独特的光化学反应机制，能够以一种与以往不同的方式控制电荷分离、热稳定性和颜色生成。
