Polymerization Photoinitiators with Near-Resonance Enhanced Two-Photon Absorption Cross-Section: Toward High-Resolution Photoresist with Improved Sensitivity

We take advantage of the near-resonant enhancement of the third-order nonlinear response to engineer a two-photon polymerization photoinitiator with optimized efficiency in regard to literature benchmarks. We study in detail its linear and resonant third-order nonlinear optical properties, with particular focus on photoinduced radical generation. Careful choice of peripheral substituents enables its direct solubilization into a mixture of commercial multifunctional acrylic monomers, resulting in a homogeneous photoresist with good optical transparency upon simple mixing. When submitted to sub-nanosecond pulsed laser irradiation at 532 nm, the resulting photoresist displays a polymerization threshold up to eight times lower than that obtained with the classically used two-photon initiators, giving rise to sub-100 nm line width at 250 nm interline separation and resulting in highly defined three-dimensional structures.