Photolysis Mechanism of Quaternary Amidinium Salts

Abstract

Photoinduced 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.

Photopolymerization activated by photobase generators and applications: from photolithography to high-quality photoresists

“…16,35 As ideal substitutes for PAGs, PBGs activate photopolymerization by generating strong bases, and PBGs exhibit better stability in air, lower costs, poor reactivity with metals and a lower susceptibilities to the degradation or corrosion processes resulting from the strong acidities of PAGs after processing. [36][37][38] With the rapid development of artificial light sources, PBGs that are sensitive to longwavelength light have been used in photopolymerizations because of their specific advantages at visible light wavelengths, including safety and the high energy processes seen with light emitting diodes (LED). 37,39,40 However, fewer PBGs have been reported in past decades compared with PAGs, thus hindering development for practical application.…”

Graphite Nitride Carbon (g-C3N4) and Borates as Near-UV Heterogeneous Photoinitiators for Acrylate Photopolymerization

“…In contrast to amines, alkylphenylborates exhibit improved photooxidation resistance and are less susceptible to yellowing. Alkylphenylborates and dye molecules have often been used together for visible-light or near-infrared-light photopolymerization, , where the alkylphenylborate anions and the dye molecules act as donors and acceptors of electrons, respectively, to enable electron transfer for the formation of free radicals that induce photopolymerization. , Inspired by this, we envisioned the potential of using borates for g-C 3 N 4 -based heterogeneous PIs instead of amines.…”