Photoresponsive Hexaarylbiimidazole-Crosslinked Hydrogels: From Synthesis to Diverse Applications

The development of light-sensitive hydrogels with rapid and on-demand responses stands represents an important outstanding challenge for developing flexible devices. Here, a light-sensitive divinyl monomer, bis(2-methacrylamidoethyl) 4,4'-(4,4',5,5'-tetraphenyl-2'H-[1,2'-biimidazole]-2,2'-diyl)dibenzoate (HABI-diMAm), was synthesized and further copolymerized with N-(hydroxymethyl)acrylamide (N-MA), leading to the formation of a photoresponsive single network hydrogel (G1) that undergoes a reversibly dynamic transformation from gel to sol upon 405 nm light irradiation, enabling a flexible non-contact dynamic information display system. With the introduction of an additional permanent covalent crosslinker, a dual-crosslinked single network hydrogel (G2) was developed as a flexible actuator that responds to light-irradiation within seconds. Next, X-ray-activated persistent luminescent nanoparticles (X-PLNPs) were incorporated into the dual-crosslinked single-network network hydrogel, leading to hybrid hydrogel (G3) that acted as a flexible X-ray scintillator screen with light-controlled self-fitting properties on non-planar substrates. The X-ray imaging results demonstrated successful recording of clear images that precisely reflect the real defects in the targeted non-planar object. Hence, the introduced HABI-crosslinked hydrogels have broad potential as photoresponsive hydrogels.