Two-photon photopolymerization using novel asymmetric ketocoumarin derivatives

A series of stilbene modified asymmetric ketocoumarin derivatives (compounds 1–4) with varied electron-donating terminal groups used on two-photon photopolymerization were reported. Solvatochromism analysis showed that the compounds with strong electron-donating terminal groups exhibited larger dipole moment change than those with weak electron-donating groups upon excitation. In addition, these compounds with strong electron-donating groups presented excellent two-photon absorption properties. Their two-photon absorption cross-sections are two magnitudes larger than those of common UV–vis sensitive photosensitizers. The results of photobleaching and one-photon polymerization experiments also showed that these compounds had high photoactivity on photosensitized photolysis of o-chloro hexaarylbiimidazoles (o-Cl-HABI) and 4,4′-dimethyldiphenyliodinium hexafluorophosphate (DPI) to generate radicals. As an example, the combination of compound 4 with o-Cl-HABI, an efficient two-photon photopolymerization initiation system, has been preliminarily demonstrated for fabrication of 3D micro-structures.