Control of Intramolecular Isomerization Reactivity of an Azobenzene Derivative Anchored to ZrO₂ Nanoparticle Thin Films

Chemical adsorption of molecules to nanomaterials imparts thermodynamic and kinetic variations to molecular reactivity. However, these differences are challenging to measure or predict and thus are frequently overlooked in nanomaterial/molecular interfacial systems. In this study, interfacial attachment of an azobenzene derivative to ZrO₂ nanoparticle thin films more than doubles the azobenzene thermal isomerization rate and decreases the extent of photoisomerization by up to a factor of 3 compared to that of fluid solution. The magnitude of these changes can be controlled by selectively anchoring either the <i>cis</i> or <i>trans</i> isomer of azobenzene to the ZrO₂ film. Furthermore, the coadsorption of the sterically hindering molecule chenodeoxycholic acid to a ZrO₂ thin film previously treated with <i>cis</i>-azobenzene results in a decreased extent of isomerization that mimics the <i>trans</i>-azobenzene anchored ZrO₂ film. Accordingly, steric hindrance of the azobenzene isomerization at the interface is implicated as an explanation for the observed variations in the reaction dynamics