Luis Pinero-Santiago - Solvent Dependence of the Photophysical Properties of 2-Chlorothioxanthone, the Principal Photoproduct of Chlorprothixene

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      2-chlorothioxanthone (CTX) is used as photoinitiator for the   reticulation of synthetic resins and for the preparation of   pharmaceuticals. It was previously determined that CTX is the   primary photoproduct of z-chlorprothixene (CPTX) when irradiated   at 313 nm and is formed in an autocatalyzed reaction through an   energy-transfer mechanism (Pin˜ ero et al. [2009] Photochem.   Photobiol., 85, 895–900). In this work, the photophysical   properties of CTX were measured in acetonitrile ⁄ water solutions   to determine if their magnitude can affect the side effects of   CPTX. The results show that CTX has higher absorption   coefficients in the visible region (400–420 nm) and higher   triplet quantum yields than its parent compound. Similar to TX,   both properties strongly depend on the solvent polarity ⁄   hydroxylicity. The quantum yield of the triplet intermediate is   very close to the value of the phenothiazine triplets. The   phenothiazines are the most phototoxic antidepressants.   Therefore, given the appropriate microenvironment, the   photosensitization side effects of CPTX can be intensified on the   production of CTX.

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