One/two-photon cationic polymerization in visible and near infrared ranges using two-branched sulfonium salts as efficient photoacid generators

This paper describes the synthesis and photochemical behavior of two two-branched sulfonium-based photoacid generators (PAGs). The branched structure influences the optical properties of the PAGs by increasing absorption wavelengths and molar extinction coefficients as well as enhancing acid production under one/two-photon irradiation. The two-branched structures collectively showed twofold higher H+ production abilities and improved two-photon absorption cross-sections compared with those in the corresponding mono-branched PAGs. Photochemical mechanisms were investigated through UV-Vis spectra analysis, molecular orbital calculations, and fluorescence analysis. These novel two-branched D-pi-A type sulfonium-based photoinitiating systems are efficient cationic photoinitiators (epoxide conversion = 70%-85% and vinyl conversion > 75%) even under conditions with low initiator concentration (1 wt%) and curing light intensities (5 mW cm(-2)) upon exposure to visible light-emitting diodes (e.g., 405 nm). These two-photon fabricated microstructures also exhibit potential as cationic two photon initiators. (C) 2016 Elsevier Ltd. All rights reserved.