Abstract
Benzylidene ketones (BK) are promising visible photoinitiator due to their facile synthesis and photochemical hydrogen atom transfer (HAT) reaction between tertiary amines. However, the effect of electron donating (ED) groups on their photophysical, electrochemical properties, and initiation efficiency were not fully disclosed. Moreover, it is not clear which co-initiator is suitable for BK. In this work, four benzylidene ketones bearing hydrogen (C3PH), methoxy (C3PO), methylthio (C3PS), and dimethylamine (C3PN) substitution were synthesized and characterized. BK’s maximum light absorption wavelengths increase following the order of C3PH < C3PO < C3PS < C3PN. Photopolymerization and steady state photolysis show that only C3PO and C3PS display higher HAT efficiency than C3PH, which is highly relating to the free energy change calculations results. Overall, C3PO is the most efficient one because good polymerization rate and final monomer conversion can be achieved. Triethanolamine is the best co-initiator because of its low oxidation potential and the lowest energy barrier to form a complex with C3PO.
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