High-performance LED induces cationic photopolymerization using novel 1,3,5-triaryl-2-pyrazoline as photosensitizer

A series of 1,3,5-triaryl-2-pyrazolines was designed and synthesized as photosensitizers for cationic photo polymerization (CP). The light absorption within the ultraviolet-visible (UV-vis) range (lambda(max) = 344-376 nm; epsilon(max) = 17,300-20,000 M-1 cm(-1)), which was strongly influenced by the substituents on the C3 atom of pyrazoline ring, matched the emission of light-emitting diodes (LEDs) within 365-425 nm. The pyrazolines, together with iodonium salt (Iod) or sulfonium salts, can generate acid upon the irradiation with LEDs, and the quantum yields of the systems were high enough (0.11-0.17 for Iod and 0.04-0.12 for sulfonium salts) for high-performance LED-induced CP at 365-425 nm irradiation. UV-vis spectra, theoretical calculation, electrochemistry, electron spin resonance-spin trapping, and fluorescence quenching were investigated to determine the photochemical mechanism. The introduction of electron-pushing group and heterocycle rings can efficiently enhance the sensitization capabilities of pyrazolines to onium salts. These pyrazoline-based photoinitiating systems have promising applications in LED-induced photopolymerization.