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Photoinitiators (Pt) are the key component in UV curable formulations. Usual drawbacks of this
component are the limited quantum yield and the limited spectral range of light which leads to the excited triplet state and thus radical formation. To increase triplet state excitation, photosensitizers (PS) are added to PIs in radiation curable 1 As demonstrated in Scheme the PS is cabable of transferring its triplet state energy directly to the P1 thus enhancing its triplet state formation. Moreover, PS expand the absorption range since their excitation (n_+Tr*) usually requires less energy compared to a-cleaving PIs. Various combinations of Pis and PS5 have been investigated in the last 23 and are also commercially available. An excellent review about the sensitizing effect of thioxanthones on a large variety of photoinitiators has been 1 Because sensitation requires close 4 copolymerizable derivatives of thioxanthones and aminoalkyiphenones have been prepared and 5 It has been found that the rate of excitation transfer is two orders of magnitude higher than that observed for physical.
