Thioxanthone acetic acid ammonium salts: highly efficient photobase generators based on photodecarboxylation

A series of photobase generators (PBGs), which contain thioxanthone as the chromophore and different quaternary ammonium salts as latent active species, were straightforwardly synthesized in two steps and their structures were characterized. Investigation on the photophysical properties of the PBGs indicated that the PBGs were photosensitive to long wavelengths due to the characteristic absorption of thioxanthone at 380 nm. A study on photolysis confirmed the photoinduced decarboxylation mechanism, through which the PBGs released active basic species efficiently. All the novel PBGs showed high activity in catalysing thiol-epoxy polymerization without postexposure baking. This is especially true for the PBG containing 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), which exhibited a faster polymerization rate and higher epoxy conversion than the previously described highly active PBG system.