Photolysis Mechanism of Quaternary Amidinium Salts

Abstract

AbstractPhotoinduced polymerization reactions are an energy‐saving and environmentally friendly technology used in applications such as curing and coating. Photo initiators are one of the key materials which generate active species by photoirradiation. Many types of radical and cationic photo initiators (photoacid generators) have been developed. However, anionic photo initiators (photobase generators), which are more advantageous in terms of corrosion and lack of deactivation, remain under development. Cyclic amidine compounds, such as DBU® (1,8‐Diazabicyclo[5.4.0]undec‐7‐ene) and DBN (1,5‐Diazabicyclo[4.3.0]non‐5‐ene), are strong organic bases, widely used as catalysts in organic, polymerization, and crosslinking reactions. Developing a photobase initiator that can generate such a strong base is important, because there are few photobase generators with strong basicity and high reactivity for practical applications. In this study, we investigated the elementary mechanism of photolysis of quaternary amidinium borate salts by transient absorption measurements. We confirm that photoinduced electron transfer is a key step in the photo decomposition of quaternary amidinium borate salts and that the position of the sensitizing chromophore in the molecules significantly affects the decomposition efficiency.