Synthesis of novel 2-(3′-dialkylaminopropoxy)-thioxanthone derivatives. photochemistry and evaluation as photoinitiators of butyl acrylate polymerization

Abstract

We report the synthesis of novel derivatives of thioxanthone with built-in tertiary amino groups. The aim of tailoring these new structures was to have photoinitiators which could react into the photocurable formulation so that the chromophore becomes attached to the polymer matrix, so reducing the possibility of it being extracted by solvents. The general photochemistry was studied by measurements of u.v. absorption, fluorescence and phosphorescence; a photoreduction study was carried out. Luminescence properties have shown the importance of the built-in amino group in the behaviour of the singlet and triplet excited states. Photoreduction quantum yields of aminopropoxythioxanthones are low, confirming that the amino group acts as a quencher of the excited state as well as a hydrogen atom donor. Polymerization quantum yields, determined by photocalorimetry in the presence of oxygen, are slightly higher with aminopropoxythioxanthones than with simple 2-propoxythioxanthone.