Photoinitiators with functional groups. VI. Chemically bound sensitizers

Several benzophenone- and thioxanthone-based photosensitizers (PSs) were covalently bonded to hydroxyalkylphenone- and aminoalkylphenone-based photoinitiators (PIS) to enhance the rate of the excitation-transfer effect due to the close vicinity of the PS to the PI. The properties of these new systems were investigated with UV spectroscopy and photo-differential scanning calorimetry. Broadband irradiation experiments and selective excitation of the PS were carried out for the physical mixtures and covalently bonded PI/PS combinations to investigate the effect of excitation transfer. Selective excitation of the PS chromophore revealed that the energy transfer was significantly increased in covalently bonded initiators in comparison with the physical mixtures. This effect was most pronounced for the hydroxyalkylphenones that were sensitized by suitable benzophenone derivatives, especially at low PI concentrations. (C) 2004 Wiley Periodicals, Inc.