Electronic Effects and Steric Effects for the Design of N-Sulfonate Ester Phthalimide Photoacid Generators with High Acid Production Efficiency and Thermal Stability

N-(p-Toluenesulfonyloxy) phthalimides have been widely used in chemically amplified photoresist systems as a photoacid generator; however, their derivatives are yet to be well developed and applied. In the current work, six N-sulfonate phthalimide derivatives with different electron-withdrawing and electron-donating substitutes were synthesized. The single crystals of these N-sulfonate phthalimide derivatives were cultured, and their crystal data were applied to theoretically calculate the bond dissociation energy of their N–O bonds and the frontier molecular orbitals. The influence of these substitutes on the electronic effects and steric effects of the N-sulfonate phthalimide derivatives was well explored and discussed. To better evaluate the performance of these N-sulfonate phthalimide derivatives, they were also mixed with poly(4-hydroxystyrene) and their acid generation efficiency and thermal stability were analyzed in the application scenarios. Our research reveals that the introduction of electron-withdrawing groups to the sulfonate moiety can effectively improve the acid generation efficiency of the sulfonate phthalimide derivative photoacid generators. This study can provide a glimpse into the future R&D of photoacid generators.