Shifting from UV to Visible-Light the Activity of Organic Photoinitiators via the Covalent Grafting of Polyoxometalates

Anthracene-,
benzophenone-, and anthraquinone-based UV
photoinitiators
have been, respectively, covalently grafted on the [Mo6O19]2– polyoxometalate (POM) platform,
affording highly colored charge transfer organo-imido Lindqvist complexes.
It has been evidenced that photosystems combining N-methyldiethanolamine (MDEA) as the electron donor and these hybrid
POMs promote free-radical photopolymerization of acrylate monomer
derivatives under irradiation in the visible range, while in similar
conditions, no polymerization was observed considering as photoinitiators
a mixture of the organic and POM precursors. After 800 s, acrylate
conversion yields up to 90% under 405 nm LED irradiation and 50% under
470 nm LED irradiation were thus obtained considering the POM-imidoanthraquinone
(POM-AQ) compound. This shows that such organo-imido
Lindqvist species can represent new easy-to-synthesize, efficient
visible-light photoinitiators. Moreover, due to the presence of the
POM, coatings prepared using the POM-AQ/MDEA/soybean
oil epoxidized acrylate photosystem exhibit excellent mechanical properties,
with very good flexibility, resistance to brittle fracture, and adherence
to the steel. Finally, POM-AQ was shown to have a remarkable
capacity to generate singlet oxygen species under visible light irradiation,
and the antibacterial activity against Staphylococcus
aureus under solar light of the related POM-derived
surface has been demonstrated.