Tuning the Thermal Stability of Tetra-o-chloroazobenzene Derivatives by Transforming Push-Pull to Push-Push Systems.

Molecular photoswitches provide interesting tools to reversibly control various biological functions with light. Thanks to its small size and easy introduction into the biomolecules, azobenzene derivatives have been widely employed in the field of photopharmacology. All visible-light switchable azobenzenes with controllable thermostability are highly demanded. Based on the reported tetra-o-chloroazobenzenes, we synthesized push-pull systems, by introducing dialkyl amine and nitro groups as strong electron-donating and electron-withdrawing groups on the para-positions, and then transformed to push-push systems by a simple reduction step. The developed push-pull and push-push tetra-o-chloroazobenzene derivatives displayed excellent photoswitching properties, as previously reported. The half-life of the Z-isomers can be tuned from milliseconds for the push-pull system to several hours for the push-push system. The n-π* and π-π* transitions have better resolution in the push-push molecules, and excitation at different wavelengths can tune the E/Z ratio at the photostationary state. For one push-pull molecule, structure and absorption spectra obtained from theoretical calculations are compared with experimental data, along with data on the push-push counterpart.

Synthesis of Halogenated Dibenzo[1,2,6]triazonines and Late-Stage Functionalization of the Triazonine Ring.

Dibenzotriazonine represent a new class of nine-membered cyclic azobenzenes with a nitrogen atom embedded in the bridging chain. To enable future applications of this photoactive backbone, we propose in this study the synthesis of mono- and dihalogenated triazonines, that allow the late-stage introduction of different functionalized aryl groups and heteroatoms (N, O, and P) via palladium-catalyzed reactions. Indeed, different diphenylphosphoryl-triazonines were synthesized with functional groups such as aniline or phenol. Bis(diphenylphosphoryl)phenyl mono- and bis-carbamate-triazonines were also isolated in good yields.

Synthesis and Characterization of a [1,2,6]Diazaphosphonine Oxide: An Example of a Photoswitchable Phosphorus-Containing Cyclic Azobenzene.

We report herein the synthesis and characterization of a phosphorus-containing cyclic azobenzene as a new photoswitchable scaffold. This backbone reveals high bidirectional photoswitching yields and high thermal stability for both isomers, with t1/2 > 90 days at 60 °C. Both E- and Z-isomers have been characterized by UV-vis spectroscopy and X-ray crystallography.

Synthesis and properties of photoswitchable diphosphines and gold(I) complexes derived from azobenzenes.

Diphosphines displaying azobenzene scaffolds and the corresponding bis-gold chloride complexes have been prepared and fully characterized by photophysical, spectroscopic and X-ray diffraction studies. DFT calculations provide complementary information on their electronic, structural and spectroscopic properties. Comparative investigations have been carried out on compounds featuring phosphorus functions in the meta- and para-positions, respectively, with respect to the azo functions, as well as on diphosphines with an ortho-tetrafluoro substituted azobenzene core. The effects of the substitution patterns on structural and spectroscopic properties are discussed.

Triazonine-based bistable photoswitches: synthesis, characterization and photochromic properties.

We disclose here dibenzotriazonines as a new class of nine-membered cyclic azobenzenes displaying a nitrogen function in the saturated ring chain. The specific features of these compounds are (i) a preferred E-configuration, (ii) high bi-directional photoswitching and (iii) good thermal stability of both E- and Z-forms.