Photochromic evaluation of 3(5)-arylazo-1H-pyrazoles.

The desire to photocontrol molecular properties ranging from materials to pharmacology using light as an external trigger with high spatiotemporal resolution lead to the development of a broad range of photochromic scaffolds. Amongst them, azobenzenes are synthetically well accessible and show excellent fatigue resistance. Their photochromic properties vary with the substitution pattern and for different heteroarenes. However, the photochromism of 3(5)-substituted-1H-pryazoles has not yet been investigated although this compound class offers interesting possibilities of metal ion coordination and hydrogen bond formation via its NH-moiety. Herein, we present the results of an experimental and computational investigation of arylazo-3(5)-arylazo-1H-pyrazoles. To elucidate their properties, solvent and substitution effects on their light absorption, thermal half-lives, photostationary states (PSS), fatigue and quantum yields were determined.