Interaction mechanism in pyrromethene dye/photoacid generator photosensitive system for high-speed photopolymer

The sensitization mechanism of a photoacid generator (PAG), N-(trifluoromethanesulfonyloxy)-1,8-naphthalimide (NIOTf) by a pyrromethene sensitizing dye, such as 1,3,5,7,8-pentamethyl pyrromethene BF2 complex (HMP), 2,6-diethyl-1,3,5,7,8-pentamethylpyrromethene BF2 complex (EMP), and 2,6-diethyl-8-phenyl-1,3,5,7-tetramethylpyrromethene BF2 complex (EPP), was studied by means of absorption and fluorescence spectroscopies, product analysis and nanosecond laser flash photolysis. For all the systems pyrromethene/NIOTf, the fluorescence quenching was nearly diffusion-controlled. This reaction involves an electron-transfer process from the excited singlet state of the pyrromethene derivative to NIOTf, as supported by the negative values of the Gibbs free energy change and the observation of the pyrromethene radical cations. The triplet state of the pyrromethene dyes was found to be unreactive toward NIOTf. Photoacid generation quantum yields for the sensitization were also measured and they showed a correlation with the electron-transfer rate constant from the dye singlet excited state. Finally, the system EPP/NIOTf was applied to printing technology with an appropriate binder polymer bearing an acetal protection group. By controlling the exposure energy and the post-exposure baking (PEB) process, a printing plate was obtained with a high resolution.