Push–pull biphenyl–based iodonium salts: Highly sensitive one-component photoinitiators for photopolymerization under UV–visible LEDs.

Diaryliodonium salts play an important role as highly efficient photoinitiators in the field of photopolymerizations. They can rapidly photodecompose to produce free radicals and super acids; thus, can initiate highly efficient photocuring of acrylic and epoxy monomers and resins. However, the absorption of commercialized diphenyliodonium salts is poorly matched with popular LED light sources, and the participation of sensitizers is usually required to achieve efficient photoexcitation. Here, we synthesized five new phenyl biphenyl iodonium salts with different electron-pushing and electron-withdrawing substituents, e.g., methoxy and CN, at the biphenyl substituent. Our results demonstrate that all synthesized iodonium salts have strong absorption in the range (λ max = 258–352 nm; ε max = 21,300–29,900 M−1 cm−1). The photochemistry of these synthesized iodonium salt is strongly influenced by substituents on the biphenyl ring. All iodonium salts can undergo rapid photolysis under light excitation, with higher quantum yield of photoacid generation reaching 0.25 and can quickly initiate cationic photopolymerization of epoxy monomers. Furthermore, free radicals are generated during photolysis, which can successfully trigger free radical polymerization. These iodonium salts with good absorbance in the UVA band demonstrate their potential as excellent photoinitiators under 365–405 nm LED excitation. Five long-wavelength LED sensitive iodonium salts with different substituents were designed and synthesized as photoinitiators for the photopolymerization process. [Display omitted] • Five push–pull biphenyl–based iodonium salts were designed and synthesized. • The photophysical and photochemical properties of iodonium salts are strongly influenced by substituents on the biphenyl ring. • The optimized iodonium salts are highly sensitive to UV–Vis LEDs @365–405 nm. • The iodonium salts can effectively initiate cationic/radical photopolymerization. [ABSTRACT FROM AUTHOR]