Blue-to-Red Light Sensitive Push-Pull Structured Photoinitiators: Indanedione Derivatives for Radical and Cationic Photopolymerization Reactions

The actual photonitiators PI can only operate in a restricted part of the visible spectrum; as a consequence, several Pis are usually necessary to harvest all the emitted visible photons. In the present paper, new dyes based on a donor-pi-acceptor structure (1,3-indanedione derivatives) are incorporated into visible light sensitive photoinitiating systems of polymerization. They exhibit an unusual and remarkable broad absorption lying from the blue to the red. When employed in the presence of an iodonium salt (Iod) and optionally N-vinylcarbazole (NVK), these dyes can efficiently initiate the radical photopolymerization of acrylates, the cationic photopolymerization of epoxide and vinylether monomers and the hybrid cure of acrylate/epoxide blends under exposure, e.g, at 405, 457, 473, 532, and 635 nm. They partly behave as organic photocatalysts. These particular light absorption properties and the initiation step mechanisms are investigated in detail.