An Ultralow-Loading Iodinated BODIPY-Based Photosensitizer Enables Fast Visible-Light Photopolymerization

Abstract

Visible-light-induced photopolymerization technology is widely employed in modern industries such as 3D printing, hydrogels, and intelligent materials. However, high-performance photoinitiators and photosensitizers that are well matched to visible-light sources remain scarce, posing a persistent challenge. Herein, we report a BODIPY-based photosensitizer (I-BDP) that enables highly efficient photopolymerization under green LED irradiation at an ultralow loading (0.0005 mol % relative to the monomer). Iodine substitution was introduced to enhance intersystem crossing (ISC) by the heavy-atom effect, giving I-BDP a long lifetime of excited triplet state (4.7 μs). This long-lived excited state facilitates photoinduced electron transfer with the co-initiators, thereby accelerating the polymerization process. A series of co-initiators, including iodonium salts, borates, thiols, aromatic amines, and hexaarylbiimidazole (HABI), were employed to construct photoinitiating systems with I-BDP. As a result, I-BDP delivers a maximum polymerization rate exceeding 50 s–1 and a curing depth of 6.8 cm, demonstrating excellent deep-curing capability. Notably, in combination with HABI, I-BDP enables, for the first time, the fabrication of long-wavelength-sensitive dry film photoresists with high resolution. These results establish I-BDP as a highly efficient visible-light photosensitizer for deep-curing applications and advanced photofabrication.