Donor–Acceptor Type Thioxanthones: Synthesis, Optical Properties, and Two-Photon Induced Polymerization

A set of thioxanthone derivatives bearing strongly electron-donating dialkylamino groups have been synthesized efficiently via the Buchwald–Hartwig, Sonogashira, and Heck reactions. Compounds possessing both one and two donors have been prepared. Their optical properties proved to be intriguing. The presence of the amino group alone increased the fluorescence quantum yield 100 times. Dyes possessing arylethylene and arylethynyl linkages absorbed UV radiation and violet light while emitting (weakly) red light, as a consequence of different geometries at ground and excited states. Our design led to an increase in two-photon absorption cross sections at the wavelength of interest (800 nm) to the highest values ever recorded for thioxanthones, while maintaining excellent solubility due to the fact that all new photoinitiators are highly viscous oils at room temperature. Some of the prepared D−π–A−π–D systems also proved to be initiators in two-photon polymerization.