o-Fluoroazobenzenes as Readily Synthesized Photoswitches Offering Nearly Quantitative Two-Way Isomerization with Visible Light

Abstract

Azobenzene functionalized with ortho-fluorine atoms has a lower energy of the n-orbital of the Z-isomer, resulting in a separation of the E and Z isomers' n→π* absorption bands. Introducing para-substituents allows for further tuning of the absorption spectra of o-fluoroazobenzenes. In particular, electron-withdrawing ester groups give rise to a 50 nm separation of the n→π* transitions. Green and blue light can therefore be used to induce E→Z and Z→E isomerizations, respectively. The o-fluoroazobenzene scaffold is readily synthesized and can be inserted into larger structures via its aryl termini. These new azobenzene derivatives can be switched in both ways with high photoconversions, and their Z-isomers display a remarkably long thermal half-life.

Halogen-Bonded Photoresponsive Materials

“…Such compounds were reported in Bushuyev et al [65]. In the material design, useful suggestions given in Bléger et al [66] were taken into account, as it was found that extremely long cis-isomer half-lives are characteristic of o-fluorinated azobenzenes. Symmetrically substituted 4-haloperfluoro azobenzenes were thus prepared (Fig.…”

Efficient Light-Induced Phase Transitions in Halogen-Bonded Liquid Crystals

“…Various structures for bistable azobenzene photoswitches have been developed, 14−17 and, among them, ortho -fluorinated azobenzenes appear particularly promising. 14,15 Fluorination is also an effective strategy to tailor the anisotropy and viscoelastic properties of LCs, 18,19 and boost intermolecular interactions for the self-assembly of supramolecular LCs. Combining these design principles, here, we target a new family of azobenzene-based, fluorinated supramolecular LCs with predictable phase behavior and efficient light-control over the molecular alignment.…”

Thermal Isomerization of Hydroxyazobenzenes as a Platform for Vapor Sensing

“…The power of azobenzenes lies in the fact that the lifetime of the metastable cis -isomer can be controlled over a wide range, from milliseconds in push–pull azobenzenes 14 up to even several months in ortho -substituted azobenzenes. 15 While fast thermal relaxation is useful in, for example, optical switching 16 and the long-lived cis -state desired in photobiology, 17 azobenzene derivatives whose thermal isomerization dynamics depends strongly on the environmental conditions are particularly interesting. As the most prominent example, 4-hydroxyazobenzenes can experience a change of up to 5 orders of magnitude in the cis -lifetime in nonpolar versus polar solvents due to hydrogen-bond-assisted tautomerization.…”