Rational Engineering of an Aza‐BODIPY Oxime Ester for Efficient Deep Photocuring Under Long‐Wavelength Light Irradiation

ABSTRACT Overcoming the limitations of conventional ultraviolet (UV) photoinitiators in biomedical applications, such as shallow curing depth and cytotoxicity, requires the development of efficient long‐wavelength‐activatable systems. Herein, we report the rational design of BDP‐OXE‐Me, a novel oxime ester‐functionalized aza‐boron‐dipyrromethene (Aza‐BODIPY) photoinitiator optimized for deep photocuring. This molecule exhibits a strong absorption maximum at 680 nm with a high molar extinction coefficient (ε) of 8.02 × 10 4 M − 1 cm − 1 , enabling activation within the red‐to‐near‐infrared window. As a single‐component type I photoinitiator, BDP‐OXE‐Me successfully initiated the free radical polymerization of trimethylolpropane triacrylate (TMPTA) under light irradiation. More significantly, a two‐component system comprising BDP‐OXE‐Me and iodonium salt (ION) sensitizer achieved efficient deep photocuring under low‐intensity 680 nm LED light, curing TMPTA into a robust, millimeter‐scale polymer film with a thickness of 0.5 mm. Mechanistic studies confirm that the oxime ester moiety enhances intersystem crossing (ISC) to populate reactive triplet states (T n ), while thermodynamic analysis reveals a spontaneous photoinduced electron transfer (PET) pathway (Δ G et = −0.389 eV) with ION. This work positions oxime ester‐modified Aza‐BODIPY hybrids as transformative platforms that show promise for deep‐penetration, biocompatible photopolymerization in precision biomedicine and advanced manufacturing.