Abstract
The first tetraacylstannanes Sn[(CO)R]4 (R=2,4,6‐trimethylphenyl (1 a) and 2,6‐dimethylphenyl (1 b)), a class of highly efficient Sn‐based photoinitiators, were synthesized. The formation of these derivatives was confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. The UV/Vis absorption spectra of 1 a, b reveal a significant redshift of the longest wavelength absorption compared to the corresponding germanium compounds. In contrast to the known toxicity of organotin derivatives, the AMES test and cytotoxicity studies reveal intriguing low toxicity. The excellent performance of 1 as photoinitiators is demonstrated by photobleaching (UV/Vis) and NMR/CIDNP investigations, as well as photo‐DSC studies.
Highlights
The first tetraacylstannanes Sn[(CO)R]4 (R = 2,4,6trimethylphenyl (1 a) and 2,6-dimethylphenyl (1 b)), a class of highly efficient Sn-based photoinitiators, were synthesized
To date, phosphorousbased initiators are well established, UV light is required for sufficient photocuring and the parent compounds, as well as their photoproducts are in most cases highly toxic.[10,11,12]
Germanium-centered PI systems have emerged over the past few years as promising alternatives due to their low toxicity and the bathochromic shift of their longest-wavelength absorption bands.[6,13,14,15]
Summary
Fast photobleaching of the initiator is an indication for efficient radical formation and is crucial for achieving high curing depths and colorless polymers.[31] Compound 1 b exhibits the fastest photobleaching, whereas bisacylphosphane oxide 3 shows almost no bleaching, being unsuitable for curing applications in this wavelength region. The superior photobleaching performance of tetraacylstannanes 1 over the reference initiators 2 and 3 upon irradiation with high wavelength visible light (470 nm) is consistent with the bathochromically shifted absorption spectra (Figure 2).
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