Pyrrole-based enone dyes as radical photointiator under 405/460 nm LED lamp: The effect of ketone structure

Abstract Enone dyes have gained tremendous attention as photoinitiator in visible light induced photopolymerization. However, the structure-relationship of the enone’s photochemical-reactivity, which strongly determined their initiation efficiency, were not fully uncovered. In this work, pyrrole-based enones (PYOs) were synthesized by the condensation of N-methypyrrole-2-aldehyde and four different ketones, yielding C3PY, C6PY, C6NPY, and C6SPY. It was found that variation of ketone part slightly affected their absorption properties but significantly changed their photophysical behavior. Accordingly, initiation performance of PYOs toward an acrylate monomer, when co-used with onimum salt or triethanolamine as additives, differentiated with each other, which is in in line with the photolysis experiment results. DFT calculation proved that imposing a six-member ring on ketone part decreases the molecular planarity of C6PY, C6NPY, and C6SPY, which in turn, enhances their internal conversion yield and decrease their photochemical reactivity. This work provides meaningful information for the structure-property relationships territory of enone dyes.