Computational Design and Synthesis of a Deeply Red Shifted and Bistable Azobenzene
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 p* 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 p* 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.
Journal of the American Chemical Society