Efficient Photoinitiators for Two-Photon Polymerization
Two-photon polymerization (2PP) is a versatile laser fabrication technique that allows the creation of 3D structures at micro- and nanometer precision. The structures are created additively in direct accordance to a computer-aided design. It requires tightly focused fs-pulsed light sources usually operating in the near infrared wavelength range. Despite its versatility and 3D capabilities, the low process speeds achievable has prevented the technology from its broader use in various applications. Optimizing the photopolymerizable formulations is key for increasing the writing speed and the process window making 2PP more economic and easy to use. This chapter gives an insight into optimizing photoinitiators for absorption of two photons and radical formation for subsequent photopolymerization. In particular, one compound is presented that can facilitate writing speeds above 150 mm s−1 and laser powers as low as 110 mW. Remarkably, this compound has a lower two-photon activity than its counterpart with different central acceptors. This indicates that various properties other that the two-photon absorption cross section have to be addressed for facilitating efficient initiation in two-photon photopolymerization.