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Acylgermanes: Photoinitiators and Sources for Ge-Centered Radicals. Insights into their Reactivity
journal contribution
posted on 2013-11-20, 00:00 authored by Dmytro Neshchadin, Arnulf Rosspeintner, Markus Griesser, Bernhard Lang, Sandra Mosquera-Vazquez, Eric Vauthey, Vitaly Gorelik, Robert Liska, Christian Hametner, Beate Ganster, Robert Saf, Norbert Moszner, Georg GescheidtAcylgermanes
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 × 108 and 3.2 ± 0.2 × 108 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.
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insightEPRabsorptionfemtotoluenephotoinitiatorGemagnitudedibenzoyldiethylgermane 1bondSource3.2investigationacetonitrilegermylbenzoyl radicalsbenzoyldiethylgermyldimethylpolymerizationstericallyintermediateparent 1.time scales1.20.2Acylgermanephotoexcitationrecombinebutyl acrylateoligomertriplet statepolarizationPhotoinitiator0.1DFT calculationsphotocured mixturesReactivityAcylgermaneRadicalanalysisnanosecond time scale
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