Ortho-Functionalized 5-(Aryldiazenyl)pyridines: Synthesis, Photochemical Properties and Thermal Stability

This project focuses on the design and synthesis of eleven ortho- and para-functionalized 5-(aryldiazenyl)pyridines bearing a C2-benzimidazole heterocycle. Synthetically, a sequential combination of Turbo Grignard addition to diazonium salts and cross-coupling functionalization was successfully utilized. The photochemical properties, photostationary states (PSS), and thermal kinetics of photoswitches were determined using quantitative ¹H NMR and temperature-regulated UV/Vis spectroscopy. The compounds exhibit efficient bidirectional photoisomerization induced by green (530 nm, E→Z, PSS 56-81%) and blue (447 nm, Z→E, PSS 64-80%) light, alongside high thermal Z-isomer stability (t_1/2 = 25-43 days). Notably, simultaneous incorporation of two ortho-fluorine atoms on the benzene ring and two methoxy groups on the pyridine core enabled a maximum PSS of 95% Z-isomer under 590 nm illumination and an exceptional half-life of 43 days at 25 °C. Ultimately, these switches demonstrate that precise substitution patterns allow independent optimization of switching efficiency and thermal stability. [1,2]