Thioxanthone-anthracene-9-carboxylic acid as radical photoinitiator in the presence of atmospheric air

Abstract

Thioxanthone-anthracene-9-carboxylic acid (TX-ANCA) namely 14-oxo-14H-naphthol [2,3-b]thioxanten-12-carboxylic acid, is synthesized and characterized as part of our continuing interest for syntheses of polyaromatic initiators. Photoinitiator, TX-ANCA have good absorption properties in the UV and visible region of the electromagnetic spectrum (epsilon(370): 9080 M(-1)cm(-1), epsilon(430): 6151 M-1 cm(-1)). The fluorescence quantum yield is calculated as 0.1 which is slightly higher than of the parent thioxanthone compound (phi(f): 0.07). The phosphorescence lifetime is found to be 39 ms. The possible initiating mechanism of TX-ANCA is based on photoexcitation of TX-ANCA and quenching of triplet excited states of TX-ANCA by molecular oxygen generates singlet oxygen. Singlet oxygen reacts with the anthracene moiety of TX-ANCA possibly forms an endoperoxide. The endoperoxides undergoes photochemical or thermal decomposition to form radicals which are able to initiate free radical polymerization. (C) 2018 Wiley Periodicals, Inc.