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

We computationally dissected the electronic and geometrical influences of -chlorinated azobenzenes on their photophysical properties. X-ray analysis provided the insight that -tetra--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-fluoro di--chloro () azobenzene and provided computational evidence for the superiority of this substitution pattern to tetra--chloro azobenzene. Thereafter, we synthesized azobenzene by -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 - and -conformations, which allows for the generation of unusually high levels of the -isomer by irradiation with green/yellow light as well as red light within the biooptical window.