Strain-Activated Photo-Dehalogenation Unlocks Low-Energy One and Two-Photon 3D Microfabrication

Light-induced photopolymerization is a sustainable and powerful engine in additive manufacturing for semiconductors, microelectronics, and optical devices. However, the field remains constrained by the limited availability of photoinitiators (PIs) that operate efficiently across the visible to near-infrared (NIR) spectrum and support both one-photon (1PP) and two-photon (2PP) processes. Herein, we introduce a new paradigm for PI design based on sterically activated materials, yielding a panchromatic photoinitiator for one-and two-photon polymerization. This is embodied by a regioselectively brominated N-doped polycyclic aromatic hydrocarbon, 5,14-NMI-Cz (5,14-dibromo-2-(2,6-diisopropylphenyl)-1H-benzo[lmn]carbazolo[9,1-bc][2,8]phenanthroline-1,3(2H)-dione). Through a combination of steric activation, strong charge-transfer character, and structural planarization upon excitation, 5,14-NMI-Cz enables radical generation via photo-dehalogenation under visible to NIR light, including 1064 nm lasers, at remarkably low thresholds. The initiator exhibits excellent solubility, a high two-photon absorption cross-section (68.8 GM), and compatibility with diverse monomer systems. It performs robustly as a one-component Type I initiator and as a photosensitizer in two- and three-component Type II systems, achieving efficient photopolymerization across the 405–565 nm spectrum. Applications include high-resolution 3D printing, microholography, and fluorescent microtagging, all enabled by visible or NIR activation. These findings introduce a new class of multifunctional photoinitiators with exceptional versatility for advanced additive manufacturing and secure optical encoding.