Computational Design and Synthesis of a Deeply Red-Shifted and Bistable Azobenzene

• Published in: Journal of the American Chemical Society Vol. 142; no. 14; pp. 6538 - 6547
• Main Authors: Konrad, David B, Savasci, Gökcen, Allmendinger, Lars, Trauner, Dirk, Ochsenfeld, Christian, Ali, Ahmed M
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 08.04.2020; Amer Chemical Soc
• Subjects: carbon-hydrogen bond activation; Chemistry; Chemistry, Multidisciplinary; cis-trans isomers; geometry; irradiation; nuclear magnetic resonance spectroscopy; Physical Sciences; red light; Science & Technology; ultraviolet-visible spectroscopy; OPTICAL CONTROL; BASIS-SETS; FLUOROAZOBENZENES; IN-VIVO; PHOTOSWITCHES; ISOMERIZATION
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.9b10430

We computationally dissected the electronic and geometrical influences of ortho-chlorinated azobenzenes on their photophysical properties. X-ray analysis provided the insight that trans-tetra-ortho-chloro azobenzene is conformationally flexible and thus subject to molecular motions. This allows the photoswitch to adopt a range of red-shifted geometries, which account for the extended n → π* band tails. On the basis of our results, we designed the di-ortho-fluoro di-ortho-chloro (dfdc) azobenzene and provided computational evidence for the superiority of this substitution pattern to tetra-ortho-chloro azobenzene. Thereafter, we synthesized dfdc azobenzene by ortho-chlorination via 2-fold C–H activation and experimentally confirmed its structural and photophysical properties through UV–vis, NMR, and X-ray analyses. The advantages include near-bistable isomers and an increased separation of the n → π* bands between the trans- and cis-conformations, which allows for the generation of unusually high levels of the cis-isomer by irradiation with green/yellow light as well as red light within the biooptical window.