Thermal Isomerization of Hydroxyazobenzenes as a Platform for Vapor Sensing

Abstract

Photoisomerization of azobenzene derivatives is a versatile tool for devising light-responsive materials for a broad range of applications in photonics, robotics, microfabrication, and biomaterials science. Some applications rely on fast isomerization kinetics, while for others, bistable azobenzenes are preferred. However, solid-state materials where the isomerization kinetics depends on the environmental conditions have been largely overlooked. Herein, an approach to utilize the environmental sensitivity of isomerization kinetics is developed. It is demonstrated that thin polymer films containing hydroxyazobenzenes offer a conceptually novel platform for sensing hydrogen-bonding vapors in the environment. The concept is based on accelerating the thermal cis–trans isomerization rate through hydrogen-bond-catalyzed changes in the thermal isomerization pathway, which allows for devising a relative humidity sensor with high sensitivity and quick response to relative humidity changes. The approach is also applicable for detecting other hydrogen-bonding vapors such as methanol and ethanol. Employing isomerization kinetics of azobenzenes for vapor sensing opens new intriguing possibilities for using azobenzene molecules in the future.

Functional materials based on molecules with hydrogen-bonding ability: applications to drug co-crystals and polymer complexes

“…In addition to assembling large biological molecules, hydrogen bonding has been used to construct crystalline and polymeric materials that exhibit novel and responsive properties [16][17][18][19]. One such property is the capacity to sense or recognize other molecules, which often occurs due to an interaction between the two species, such as non-covalent forces [20,21]. This review will focus on crystalline and polymeric materials that can sense and interact with pharmaceutical compounds via formation of intermolecular hydrogen bonds.…”

Photocontrol of Supramolecular Azo-Containing Block Copolymer Thin Films during Dip-Coating: Toward Nanoscale Patterned Coatings

“…34,35 However, recent research indicates that the influence of solvent on thermal isomerization kinetics is complex, involving not only the solvent polarity but also factors that include the preferred isomerization mechanism, azobenzene substituents, solution concentration, and the presence of intra-and intermolecular hydrogen bonding. [36][37][38] In our case, it is noteworthy that toluene does not form hydrogen bonds with the OH-functionalized azos, in contrast to THF, which may account for the shorter cis lifetimes in toluene, thus outweighing the effect of solvent polarity.…”

ortho-Fluorination of azophenols increases the mesophase stability of photoresponsive hydrogen-bonded liquid crystals

“…The chemistry of stilbazoles and their complexes has been pioneered by Bruce and coworkers who have reported several breakthroughs in supramolecular liquid crystals. 14,24,41 On the other hand, 4-(4′-alkylphenylazo)phenols are versatile building blocks that have proven useful in building functional polymeric self-assemblies, [42][43][44][45] but to the best of our knowledge have not been utilized in devising supramolecular small-molecule-based liquid crystals. The non-fluorinated azophenol A (99% purity) was purchased from TCI Europe and used as received.…”