Thioxanthone derivatives

The synergistic behaviour of the above systems has been explained in terms of both triplet-triplet energy transfer and photoreduction of the thioxanthone derivative by the amino group of the moipholino moiety [157-161]. 

In direct photofragmentation, the thioxanthone derivative absorbs light at about 380 nm which results in homolytlc cleavage of the methylene-halogen or sul-fonyl-halogen bonds of the parent molecule to produce... 

The story of the development of oxamniquine started from the work of Kikuth et al. [2] who introduced lucanthone (miracil D, la), a thioxanthone derivative, in the chemotherapy of schistosomiasis in 1946. In the biophase, the 4-methyl group of lucanthone is converted into the corresponding 4-hydroxymethyl derivative. This led Rosi, Berberian and their colleagues working at Sterling Winthrop to develop hycanthone (lb) as a better human schistosomicide than lucanthone [3-6],... 

Amine containing ketone based photoinitiators bearing an amine moiety in the benzophenone or thioxanthone series [162] as well as a new thioxanthone derivative (where the coinitiator such as a thiol [163], an acetic acid derivative [164,165] is grafted) have been developed (10.51) Covalently bonded camphorquinone/ amine [166] or amino alkyl ketone/thiol [167] were also recently reported. 

Energy transfer is rather seldom encountered [2j] due to the obvious difficulty to have the S triplet-state level higher than that of I. The most typical case of energy transfer is encountered between a thioxanthone derivative and a morpholino ketone derivative (10.60) the excitation moves from the thioxanthone triplet state to the morpholino ketone triplet state. With other thioxanthone derivatives, electron transfer followed by proton transfer with the amine moiety can compete to some extent [212]. The sensitized cleavage in covalently linked thioxanthone derivative/cleavable photoinitiator was recently investigated and discussed [213],... 

Photosensitizer-Linked Photoinitiator or Coinitiator-Based Systems Attempts have been made to incorporate the dye and the energy or the electron donor in the same molecule. An old example was apolymeric system where a morpholinoketone and a thioxanthone derivative were grafted [215]. A first recent example corresponds to a dye linked to a triazine derivative (10.61) where an intramolecular electron transfer yields a radical anion on the triazine moiety that results in the production of a radical [216,217],... 

In previous papers we reported on the photochemistry and photopolymerisation activity of a series of water- and oil-soluble thioxanthone derivatives (1-6). In that work, all the thioxanthone structures were found to operate essentially by a primary photochemical process of electron abstraction via an exciplex with an amine co-synergist. However, whereas the oil soluble structures were found to operate solely through their lowest excited triplet state (1,2,6) the water-... 

Various derivatives of thioxanthone are often used as photosensitizers with substituted morpholino ketones as energy aeeeptors. Aetually, the two materials by themselves are effieient initiators. It was shown that when eombinations of thioxanthone derivatives with morpholino ketones are irradiated with light, two types of reaetions ean take plaee. If the triplet-triplet energy transfer oeeurs when the energy level of the thioxanthone is higher than that of the morpholine ketone, eleavage of the morpholino ketone is the result ... 

A number of water soluble thioxanthone derivatives were prepared specially for water borne systems. They can be illustrated as follows ... 

A combination of benzophenone and 1,3-dioxane is a convenient hydrogen abstraction-type photoinitiator system for the free radical photopolymerization of methyl methacrylate, styrene and other monomers. As an advantage, this system does not require an additional hydrogen donor as other conventional initiators. In a similar way, mixtures of thioxanthone derivatives and fluorenes can be used as visible light absorbing oil- and water-soluble photoinitiators for free radical polymerization of methyl methacrylate, ethyl 2-(2-phosphonoethoxymethyl)acrylate and trimethylolpropane triacrylate. Photopolymerization and laser flash photolysis studies reveal that initiation occurs by intra- and intermolecular hydrogen abstraction by the thioxanthone-like triplet excited state. 

The most widely used commercial derivatives are 2-chlorothioxan-thone and 2-isopropylthioxanthone. iFurthermore, ionic thioxanthone derivatives have been developed, which may be employed for water-based curing formulations [145,146]. A great advantage is that thioxanthones are virtually colorless and do not cause yellowing in the final products. 

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