Enhanced One/Two-Photon Initiating Performance of Nitro-Carbazole-Styrene Based Oxime/Ketoxime Esters

Photoinitiators of the oxime ester (OXE) or ketoxime ester (OXE-CO) type can rapidly undergo N—O bond cleavage and generate free radicals to initiate photopolymerization under LED excitation, occupying an important position in the field of photocuring. However, the commercial OXEs, e.g., OXE 01 and 02 with λ_max's at 326 and 344 nm, respectively, still do not well match the emission spectra of LEDs. Developing novel OXEs/OXE-COs with high photosensitivity for long-wavelength LEDs has great significance. Here, four new OXEs/OXE-COs with nitro-carbazole-styrene conjugated chromophore were designed, synthesized, and used as photoinitiators. Results demonstrated that all photoinitiators had strong absorption within the UV–vis range (λ_max: 381—392 nm, ε_max: 8200—11500 M⁻¹·cm⁻¹). Molecular design of the oxime ester cleavage to produce a small volume methyl group and a methacryl group with an unsaturated double bond brings high activity and low migration, respectively, in one-photon polymerization under 365—450 nm LEDs excitation. Moreover, OXEs/OXE-COs with PETA exhibited a wide processing window, high resolution (line accuracy~100 nm) and good nano-patterning capability under 780 nm femtosecond laser irradiation in two-photon polymerization, indicating their great potential in 2D/3D microfabrication technologies.