Thiophene-substituted phenothiazine-based photosensitisers for radical and cationic photopolymerization reactions under visible laser beams (405 and 455 nm)

Six new thiophene-substituted phenothiazine-based photosensitizers (ThPTZs) applicable to different visible laser diodes (405 nm and 455 nm) have been synthesized successfully via the Suzuki–Miyaura coupling reaction. The presence of thiophene groups in these compounds led to significantly redshifted UV-Vis absorption, making them suitable for promoting photopolymerization under visible light irradiation. Paired with bis(4-methylphenyl) iodonium hexafluorophosphate (ION), the ThPTZ systems exhibited high efficiency in promoting the ring-opening polymerization of epoxides and radical polymerization of acrylates in air using very soft laser diodes at 405 nm and 455 nm as the light sources. The detailed photochemical mechanisms have been studied by steady-state photobleaching, fluorescence spectroscopy and cyclic voltammetry analyses.