Control over the radicals that a Type I photoinitiator releases without changing the formulation offers a direct handle on polymer microstructure. To address this challenge, molecular architectures with tailored solubility and reactivity are required. Consequently, we synthesized novel polyethylene glycol (PEG)-functionalized acylgermanes via a straightforward one-pot synthetic protocol in good yields, as confirmed by NMR spectroscopy, X-ray crystallography and UV/Vis spectroscopy. By integrating PEG-functionalized para-alkoxybenzoyl substituents two different aryl-carbonyl chromophores were introduced. UV/Vis spectroscopy and TD-DFT (CAM-B3LYP/def2-TZVP) analysis assigned complementary bands to the mesitoyl and para-alkoxybenzoyl units enabling wavelength-selective excitation. Photo-CIDNP tracked the fate of primary Ge/benzoyl radical pairs in the presence of a monomer quencher (butyl acrylate) and revealed competition between two alternative α-cleavages via CIDNP polarizations of diagnostic aldehydes. By shifting the irradiation window, the balance between mesitoyl- and para-alkoxybenzoyl-derived radicals can be systematically tuned, an effect corroborated by steady-state LED irradiation NMR experiments. Extension of this concept to other mixed tetraacylgermanes demonstrates that wavelength-selective fragmentation is a general design principle rather than a compound-specific anomaly. These PEG-acylgermanes combine polar media compatibility with light-programmable radical generation, converting small adjustments in wavelength into mechanistic control during photopolymerization.
Culum et al. (Fri,) studied this question.