A series of thioxanthone derivatives as well as the unsubstituted thioxanthone have been investigated using time resolved absorption spectroscopy either with a nanosecond or picosecond laser light source excitation. These molecules are well known as photoinitiators for the photopolymerization reaction associated to a cosynergist generally tertiary amines. Faces to the industrial increasing market drive asking for better photoinitiators for coating technology, it is necessary to improve our knowledge concerning the excited states photophysic and photochemistry of such chromophores. They exhibit a dramatic dependence on the polarity of the media which may depreciate or improve the final quality of the material or at worse a lower photoinitiating ability. The time resolved absorption spectroscopy allows us to gain valuable informations on the relative rates of concurrent state reactions for thioxanthones. In this work, the following aspects will be covered, photophysics of the excited states and photoreduction by amines. All these data will underline the role of the medium in the search to optimize photoinitiating systems such as thioxanthones.
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