Enhancement of Acid Photogeneration Through a Para-to-Meta Substitution Strategy in a Sulfonium-Based Alkoxystilbene Designed for Two-Photon Polymerization

This contribution reports on the synthesis and the photochemical behavior of two new sulfonium-based photoacid generators (PAGs). We demonstrate that a para-to-meta substitution of a methyl (p-cyanobenzyl) sulfonium group in a 4-alkoxystilbene core strongly influences the photodissociation efficiency of the PAGs and leads to an increase of the quantum yield for acid generation by a factor 2.4. This substantial effect, which was also corroborated by a reactivity enhancement in cationic photopolymerization, is assigned to the modulation of the electronic interaction between two low lying excited states whose energy gap is strongly influenced by this substitution effect. Moreover, it was found that the position of the sulfonium moiety hardly affects the two-photon absorption properties of these push-pull chromophores. By the two-photon fabrication of microstructures, we finally show the potential use of the meta derivative as cationic two-photon initiator.