Benzoylgermanium Derivatives as Novel Visible-Light Photoinitiators for Dental Composites

New dibenzoylgermanium derivatives are synthesized starting from various dithioacetal protected benzaldehydes by a coupling reaction with different dialkyldichlorogermanes and subsequent oxidative cleavage of the protecting group. The synthesized germanium compounds show a significantly stronger blue light absorption than camphorquinone. During irradiation, the dibenzoylgermanium derivatives undergo photodecomposition under formation of radicals. Therefore, the different dibenzoylgermanium derivatives are used as amine-free visible-light photoinitiators for dental cements and composites. Composites based on the different dibenzoylgermanes are storage-stable and show a significantly improved bleaching behavior over composites with CO/amine photoinitiators.