Mono- and bis-acylphosphine oxides are state of the art long wavelength photoinitiators. Compared to the classical benzoyl chromophore, the important n-pi* transition is shifted close to 400nm. In the field of dental filling materials and ceramic additive manufacturing longer wavelength photoinitiators are desired. As bimolecular systems like camphorquinone suffer from low reactivity especially in aqueous formulations, a hydrophilic bisacylphosphine oxide as been developed [1].

The long wavelength absorption behaviour of a-cleavable initiators was up to recently limited to bisacyl phosphine oxides with ~450 nm. We have now introduced germanium-based compounds that are successfully applied in dental filling materials under the tradename Ivocerin [2,3].

Based on the sucess, tetraacylgermans [4], tetraacylsilanes [5] and tetraacylstananes [6] were investigated.

[1] G. Ullrich, B. Ganster, U. Salz, N. Moszner, R. Liska: "Photoinitiators With Functional Groups. IX. Hydrophylic Bisacylphosphine Oxides for Acidic Aqueous Formulations"; J. Polym. Sci. A: Polym. Chem. 44 (2006), 1686 - 1700.

[2] B. Ganster, U. Fischer, N. Moszner, R. Liska: "New Photocleavable Structures, 4 Acylgerman-Based Photoinitiator for Visible Light Curing"; Macromolecular Rapid Communications, 29 (2007), S. 57 - 62.

[3] B. Ganster, U. Fischer, N. Moszner, R. Liska: "New Photocleavable Structures. V. Diacylgermane Based Photoinitiators for Visible Light Curing"; Macromolecules, 7 (2008), 41; S. 2394 - 2400.

[4] C. Haslinger, L. Leutgeb, M. Haas, S. Baudis, R. Liska: "Synthesis and Photochemical Investigation of Novel Tetraacylgermanes"ChemPhotoChem, (2022)

[5] M. Mitterbauer, M. Haas, H. Stüger, N. Moszner, R. Liska: "Tetrakis(2,4,6-Trimethylbenzoyl)Silane-A Novel Photoinitiator for Visible Light Curing"; Macromolecular Materials and Engineering, 302 (2017), 5; S. 1600536 - 1600542.

[6] M. Mitterbauer, P. Knaack, S. Naumov, M. Markovic, A. Ovsianikov, N. Moszner, R. Liska: "Acylstannanes: Cleavable and Highly Reactive Photoinitiators for Radical Photopolymerization at Wavelengths above 500 nm with Excellent Photobleaching Behavior"; Angewandte Chemie - International Edition, 57 (2018), 37; S. 12146 - 12150.