title: Acylgermanes: photoinitiators and sources for Ge-centered radicals. insights into their reactivity.
abstract: Acylgermanes have been shown to act as efficient photoinitiators. In this investigation we show how dibenzoyldiethylgermane 1 reacts upon photoexcitation. Our real-time investigation utilizes femto- and nanosecond transient absorption, time-resolved EPR (50 ns), photo-chemically induced dynamic nuclear polarization, DFT calculations, and GC-MS analysis. The benzoyldiethylgermyl radical G• is formed via the triplet state of parent 1. On the nanosecond time scale this radical can recombine or undergo hydrogen-transfer reactions. Radical G• reacts with butyl acrylate at a rate of 1.2 ± 0.1 × 10(8) and 3.2 ± 0.2 × 10(8) M(-1) s(-1), in toluene and acetonitrile, respectively. This is ~1 order of magnitude faster than related phosphorus-based radicals. The initial germyl and benzoyl radicals undergo follow-up reactions leading to oligomers comprising Ge-O bonds. LC-NMR analysis of photocured mixtures containing 1 and the sterically hindered acrylate 3,3-dimethyl-2-methylenebutanoate reveals that the products formed in the course of a polymerization are consistent with the intermediates established at short time scales.
authors.affiliation: Institute of Physical and Theoretical Chemistry and §Institute of Chemistry and Technology of Materials, Graz University of Technology , Stremayrgasse 9, 8010 Graz, Austria.
authors.forename: Dmytro
authors.initials: D
authors.lastname: Neshchadin
authors.forename: Arnulf
authors.initials: A
authors.lastname: Rosspeintner
authors.forename: Markus
authors.initials: M
authors.lastname: Griesser
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lang
authors.forename: Sandra
authors.initials: S
authors.lastname: Mosquera-Vazquez
authors.forename: Eric
authors.initials: E
authors.lastname: Vauthey
authors.forename: Vitaly
authors.initials: V
authors.lastname: Gorelik
authors.forename: Robert
authors.initials: R
authors.lastname: Liska
authors.forename: Christian
authors.initials: C
authors.lastname: Hametner
authors.forename: Beate
authors.initials: B
authors.lastname: Ganster
authors.forename: Robert
authors.initials: R
authors.lastname: Saf
authors.forename: Norbert
authors.initials: N
authors.lastname: Moszner
authors.forename: Georg
authors.initials: G
authors.lastname: Gescheidt
mesh_terms: D005609:Free Radicals / Q000737:chemistry; D005857:Germanium / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010782:Photolysis; D017319:Photosensitizing Agents / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D009942:Organometallic Compounds; D017319:Photosensitizing Agents; D005857:Germanium