Toward Fully Photoresponsive Amphiphilic Polymers via Azopyrazole-Functionalized Polyacrylamides

Arylazopyrazoles (AAPs) are a rapidly emerging class of photoswitches, which stand out due to their distinct absorption maxima of the E- and Z-isomers, the highly Z- or E-isomer-rich photo stationary states upon irradiation by UV- or visible light, respectively, and the long lifetime of the metastable Z-state. Here, we present water-soluble acrylamide copolymers functionalized by an AAP dye. This renders them both thermo- and photoresponsive and enables the reversible modulation of their LCST-type phase transition temperature (PTT) in aqueous solution by the E- to Z-isomerization. By alternating irradiation with UV and green light, the PTT is modulated effectively and can be shifted for optimized AAP contents by up to 27 °C, i.e., much higher than by common azobenzene photoswitches. The AAP photoswitch and the transition process of the dye-modified polymer are investigated using density functional theory calculations, turbidity measurements, and temperature-dependent NMR, EPR, and UV-vis spectroscopies.