From mono- to tetraacylgermanes: Extending the scope of visible light photoinitiators

Anna Eibel, Judith Radebner, Michael Haas, David E. Fast, Hilde Freißmuth, Eduard Stadler, Paul Faschauner, Ana Torvisco, Iris Lamparth, Norbert Moszner, Harald Stueger, Georg Gescheidt*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We have investigated the inititiaton efficiency of carefully selected germanium-based photointiators for radical polymerization. To establish a systematic relationship between structure and reactivity, we have developed a convenient synthetic protocol for the preparation of a trisacylgermane, closing the gap from mono- to tetraacylgermane photoinitiators. The studied acylgermanes display distinct, wavelength-dependent photobleaching upon irradiation up to 470 nm. In particular, tetraacylgermanes featuring ortho-alkyl substituents reveal red-shifted n-π∗ bands, in line with excellent photobleaching upon visible light irradiation. Quantum yields of decomposition (determined at 385 nm) have been found to be highest for bisacylgermanes. Germyl radicals produced upon triplet-state α-cleavage of the acylgermanes react remarkably fast with monomers. Addition rate constants to (meth)acrylates range from 0.4-4.5 × 108 M-1 s-1, depending on the substitution pattern. These values are clearly higher than those reported for related phosphorus-centered radicals derived from acylphosphane oxides. We have further established the nature of the products and side-products formed at initial stages of the polymerizations using chemically induced dynamic nuclear polarization (CIDNP) experiments.

Original languageEnglish
Pages (from-to)38-47
Number of pages10
JournalPolymer Chemistry
Issue number1
Publication statusPublished - 7 Jan 2018

ASJC Scopus subject areas

  • Bioengineering
  • Biochemistry
  • Polymers and Plastics
  • Organic Chemistry


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