1-Naphthylamine thioxanthone-based one-component visible-light photoinitiators

The introduction of substituents affects the planarity of the molecule, resulting in different physical and chemical properties. This study synthesized four one-component visible light photoinitiators with different substituents derived from 1-naphthylamine. They were amine-free (BTX), primary amine (BTX-A), secondary amine (BTX-MA), and tertiary amine (BTX-DMA). The photophysical and photochemical properties were explored using UV–visible absorption spectroscopy combined with DFT theory computational simulations. They had excellent absorption properties in the visible light range ( ε : 3200–6300 L mol −1  cm −1 ). The structure of amine substitutions in the initiators showed different redshift phenomena. The maximum absorption wavelength of BTX in the visible region is 388 nm; only a 7 nm red shift occurred for the maximum absorption wavelength of BTX-DMA. While BTX-A had a maximum absorption wavelength of red shifting by 41 nm， the red shift for BTX-MA was about 53 nm, and its UV absorption tail extended to 520 nm. This phenomenon was known to be the result of the combined effect of electronic donor and molecular planarity according to the DFT theoretical calculations. The photopolymerization kinetics of four initiators used for double bond monomers was investigated by real-time FT-IR. The results indicated that polymerization could occur for all the designed systems; the highest double bond conversion could reach 92 % when BTX-DMA was used as a visible-light photoinitiator for the monomer of 2-hydroxyethyl acrylate (HEA).