Aromatic amine–sulfone/sulfoxide conjugated D–π-A–π-D-type dyes in photopolymerization under 405 nm and 455 nm laser beams

Abstract

Based on a D–π-A–π-D structural strategy, six novel dyes (Cz–SO, Cz–SO₂, TA–SO, TA–SO₂, PTZ–SO, and PTZ–SO₂) containing triphenylamine/phenothiazine/carbazole as electron donors and sulfone/sulfoxide as electron acceptors are prepared and incorporated into a photoinitiating system, together with iodonium salt (ONI). The one- and two-photon photophysical properties of these dyes were studied. The UV-vis spectra showed red-shifts of 51 and 75 nm from N-ethyl carbazole (CZ) to Cz–SO and Cz–SO₂. Similar red-shifts were found in the other dyes. The two-photon excited fluorescence (TPEF) spectra in the range 700–880 nm were recorded and it was found that these dyes present a clear two-photon absorption (TPA). Among them, PTZ–SO₂ possesses the maximum TPA cross-section, which is 2465.5 GM. Ring-opening cationic polymerization of epoxides and free radical polymerization of acrylates upon exposure to very soft irradiation of laser diodes at 405 nm and 455 nm were performed using ONI/dyes initiating systems. Compared with the well-known camphorquinone-based systems, the combinations of the obtained dyes with iodonium salt exhibit higher polymerization efficiency. The results from photobleaching and electrochemical experiments show that these dyes could photosensitize ONI through photoinduced charge transfers. Owing to their higher polymerization efficiency and large TPA cross-section, these dyes would have extensive application prospects in the fields of photopolymerization by soft visible light irradiation sources and two-photon polymerization (TPP).