LED (385, 405 and 455 nm) induced polymerization using star-shaped tris(4-(thiophen-2-yl)phenyl) amine derivatives as light harvesting photoinitiators

International audienceTwo star-shaped tris(4-(thiophen-2-yl)phenyl)amine derivatives, namely tris(4-(5-(3-pentylthieno[3,2- b ]thiophen-5-yl)thiophen-2-yl)phenyl)amine and tris(4-(5-(3-pentyl-2-(thiophen-2-yl)thieno[3,2- b ]thiophen-5-yl)thiophen-2-yl)phenyl)amine, are developed as photoinitiators for radical and cationic polymerizations under near-UV and visible light-emitting diodes (LEDs) (e.g., 385, 405, and 455 nm). When used in combination with an iodonium salt (and optionally N -vinyl carbazole) or an amine/alkyl halide couples, they lead to excellent photoinitiating abilities for the polymerization of epoxides or (meth)acrylates under air. Compared with commercial photoinitiators, i.e., camphorquinone-based systems or bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, the novel photoinitiators exhibit noticeably higher polymerization efficiencies under air (epoxide conversions = 41–57% vs ≈0%, halogen lamp exposure; methacrylate conversions = 50–55% vs 44%, LED at 405 nm exposure; methacrylate conversions = 34–42% vs 0–8%, LED at 455 nm exposure). These systems are also interesting in overcoming oxygen inhibition. The photochemical mechanisms are studied by steady-state photolysis, electron spin resonance spin trapping, fl uorescence, cyclic voltammetry, and laser fl ash photolysis techniques