D–π–A-type Sulfonium Salt Photoinitiators for Photopolymerizations Under Near-UV and Visible Light-emitting Diodes

Abstract

A series of D–π–A-type sulfonium salt photoacid generators were designed and synthesized by molecular engineering through systematically changing electron-pushing groups, π-conjugated systems, the electron-withdrawing groups, and the number of branches. D–π–A-type sulfonium salt photoacid generators can effectively decompose under irradiation of UV–visible light-emitting diode (LED) light sources owing to the matching of their absorption spectra and the emitting spectra of LEDs. The light absorption and acid generation properties of these sulfonium salts were elucidated by UV–vis spectra, theoretical calculations, fluorescence spectroscopy, cyclic voltammetry techniques, and electron spin resonance spin-trapping techniques. Results indicate that the introduction of strong electron-donating groups, certain π-conjugated structures, certain electron-withdrawing groups or two-branched structures are beneficial for the performance of photoacid generation. Most sulfonium salts can initiate versatile photopolymerizations under irradiation by a wide variety of UV and visible LEDs and show potential as two-photon photoinitiators for microfabrication technologies.