Synthesis of Tioxanthene based photoinitiahor and investigation of photophysical and photochemical properties

Photopolymerization science and technology have become more important issue both scientifically and industrially in the recent years. Coatings, adhesives and printing inks are among these applications. Free radical polymerization is stil the most used process despite the fact that cationic polymerization have currently become more important for last years. Photoinitiators are the most important components in photopolymerization. Many researches have concentrated upon Type I photoinitiators when exposed to radiation two radical produced from ?-cleavage of type I photoinitiators. In the case of type II photoinitiators, radical generation generally occurs by the interaction of Type II photoinitiator with a hydrogen donor. The term of curing by radiation can be explained as transforming a liquid to 100% solid or changing of physical properties of a polymer. This technology generates radicals at absorbing suitable wavelength which transform multifunctional monomer to cross-linked network. These industrial applications have shown more rapid improvement by developing free radical photoinitiators which have high quantum yield.In this research, the synthesis of properties of 3-Mercapto-9-oxo-9H-tioxanthene-2-carboxylic acid (TX-TSA) was achieved and photophysical and photochemical properties of TX-TSA were investigated. In addition, explain the photoinitiation mechanism of TX-TSA, triplet state features were examined by laser flash photolysis and phosphorescence spectroscopy. It has been found that TX-TSA has a high molar absorptivity in the visible region ( ? =20666 mol. L-1. cm-1) however it has a low florescence quantum yield ( ? F=0,009). Triplet state configuration of TX-TSA is appeared as n ?? *, phosphorescence lifetime of TX-TSA was found as 115 ms and triplet lifetime was calculated as 207 ns by laser flash photolysis technique. Absorption spectrum and fluorescence emission spectrum of obtained polymer (PMMA) were confirmed that the photoinitiator was attached to polymer. Photoinitiation mechanism of this photoinitiator indicates that most probably by intermolecular hydrogen abstraction processes occurs during the polymerization reaction.