Novel photoinitiator with a radical quenching moiety for confining radical diffusion in two-photon induced photopolymerization

We designed and synthesized a novel two-photon induced photoinitiator with radical quenching moiety, 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-(4-methoxybenzyl)-carbazole (BNMBC), and successfully demonstrated its optical properties, high initiating efficiency in two-photon induced polymerization (TPIP) and capability to fabricate 3D structures with high resolution. The high resolution in TPIP using BNMBC was achieved as compared to the reported photoinitiator 3,6-bis[2-(4-nitrophenyl)-ethynyl]- 9-benzylcarbazole (BNBC). BNMBC was confirmed to have a large two-photon absorption cross-section of 2367 GM by Z-scan measurement. We investigated the photopolymerization properties of resins R-1-R-3 in which BNBC, BNBC/phenyl methyl ether (PhOMe) and BNMBC were used as photoinitiators, respectively. The TPIP fabrication experiments exhibited that BNMBC possessed high TPIP initiating efficiency and an effective radical quenching effect. The volumes of polymer fibers fabricated by the TPIP of the photoresist using BNMBC as the photoinitiator were decreased to 20%-30% of those synthesised using BNBC as a photoinitiator. The introduction of a radical quenching group to the photoinitiator resulted in the effective confining effect of radical diffusion compared to the addition of the same molar ratio of radical quencher. This kind of photoinitiator with radical quenching group should benefit the fabrication of precise structures.