Photoswitchable Branched Polyurethanes Based on Hexaarylbiimidazole for Photolithography.

Hexaarylbiimidazole (HABI) molecules have awakened a broad interest in photo-processing, super-resolution imaging, photoinduced self-healing materials, and photomechanical hydrogels due to their excellent photosensitivity and photo-induced cleavage properties. In this work, a novel photoswitchable branched polyurethanes (BPU), which are synthesized by copolymerizing HABI with glycerol, isophorone diisocyanate (IPDI), and polyethylene glycol (PEG₄₀₀), is designed. 7-Diethylamino-4-methylcoumarin (DMCO) is introduced as a radical quencher, which can not only avoid the hydroxyl interfering from conventional radical scavengers during the polymerization process but also promote efficient quenching of TPIR radicals. By optimizing the DMCO concentration, and HABI content, high-quality lithographic patterns are achieved with high film retention at low exposure doses. The branched structure exhibits superior photosensitivity and solubility after exposure compared to previous crosslinked systems. This work provides HABI-based branched polyurethane, which acts as one of the potential candidates for UV-positive photoresists.