Imidazole-containing photoinitiators for fabrication of sub-micron structures by 3D two-photon polymerization

Abstract

Three imidazole-containing compounds with a phenanthroline and phenanthrene fragment were for the first time applied as initiators of two-photon polymerization individually and in combination with amines. The characterization of the novel two-photon photoinitiators was performed both theoretically and experimentally. The conducted DFT calculations revealed a correlation between nonlinear optical properties (dipole moment, mean polarizability, anisotropy of polarizability, first hyperpolarizability) and the photoinitiating activity of the compounds in one- and two-photon polymerization. A photocomposition based on phenanthroline-containing imidazole and triethanolamine demonstrated the widest fabrication window, the highest degree of conversion, as well as the two-photon polymerization threshold two times lower than the commonly used commercial IP-L photoresist. Consequently, the most effective photocomposition was proposed as imidazole photoresist for 3D two-photon polymerization and used for the fabrication of sub-micron and cell-like polymer structures.