One/two-photon sensitive sulfonium salt photoinitiators based on 1,3,5-triphenyl-2-pyrazoline.

[Display omitted] • Three novel 1,3,5-triphenyl-2-pyrazoline-based sulfonium salts were designed and synthesized as novel photoinitiators (PIs). • The newly synthesized PIs were highly sensitive to UV–Vis LEDs (365 nm–425 nm) • The quantum yields of photoacid generation of PIs are high and wavelength-dependent. • The pyrazoline-based PIs can initiate cationic polymerization as well as free radical polymerization. • The PIs can be applied in two-photon induced lithography. Three 1,3,5-triphenyl-2-pyrazoline-based sulfonium salt photoinitiators (PIs) were synthesized, and the relationship between their molecular structures and photophysical and photochemical properties under one/two-photon irradiation were presented. The sulfonium salts had absorption peaks from 343 nm to 372 nm that overlapped the emission of 365–425 nm light-emitting diode (LED) light sources. The energy levels of molecular orbitals were closely related to the quantum yield of photoacid generation (Φ H +) as determined by the electrochemical and absorption properties of the PIs, and the introduction of an electron-pushing group could increase Φ H + due to the enlarged energy gap between the singlet excited states S 1 and S 2. Interestingly, the wavelength dependence of Φ H + was due to the nature of the transition. The π–π* transition showed high Φ H + values (0.56–0.66) under excitation by UV LEDs, while the π–σ* transition showed low efficiency under visible LED irradiation. Intramolecular charge transfer from the pyrazoline ring to sulfonium salts induced efficient photolysis and high Φ H +. The sulfonium salts could efficiently initiate cationic polymerization and free radical polymerization. In addition, their high two-photon absorption cross-sections (δ 780 nm = 75–105 GM) reduced the threshold of two-photon microfabrication. These PIs should have potential in LED photocuring and two-photon 3D microfabrication. [ABSTRACT FROM AUTHOR]