Synthesis of novel Si-based long wavelength photoinitiators for dental applications

Abstract

Visible light photopolymerization is widely used for modern applications, such as curing of dental filling materials. The currently used bimolecular photoinitiating system based on camphorquinone / dimethylamino benzoic acid ethyl ester (CQ/DMAB) shows quite limited reactivity. Other more efficient cleavable photoinitiators like bisacylphosphine oxides (BAPO) show an absorption band which does not overlap very well with the emission band of the applied dental LEDs. Also diacylgermane-based structures like Ivocerin with an absorption shifted to longer wavelengths revealed drawbacks relating to its high production costs. Since Si-based photoinitators might have similar absorption properties as the Ge-based compounds, the synthesis and photochemical characterization of such a compound should be the target of this work. Due to the low stability of the existing acylsilane-based type I initiators novel concepts should show be explored. Furthermore, improved reactivity is desired, which should be achieved by repressing the photoinduced formation of a siloxycarbene, also known as Brook-rearrangement. Therefore the synthesis of oxygen substituted acyl silanes was envisaged. Furthermore the strategy of multiple substitution at the silicon atom with aromatic acyl groups resulted in a successful synthesis of a tetraacylsilane, which showed good reactivity in photopolymerization of acrylates. Furthermore the absorption band overlaps very well with the emission band of dental LEDs. However its stability in aqueous media still leaves room for improvement.