LAUSR

The photophysical and photochemical behaviors of thioxanthen-9-one (TX) in different solvents have been studied using nanosecond transient absorption spectroscopy. A unique absorption of the triplet state 3TX* is observed, which involves two components, 3nπ* and 3ππ* states. The 3ππ* component contributes more to the 3TX* when increasing the solvent polarity. The self-quenching rate constant ksq of 3TX* is decreased in the order of CH3CN, CH3CN/CH3OH (1:1), and CH3CN/H2O (1:1), which might be caused by the exciplex formed from hydrogen bond interaction. In the presence of diphenylamine (DPA), the quenching of 3TX* happens efficiently via electron transfer, producing the TX·− anion and DPA·+ cation radicals. Because of insignificant solvent effects on the electron transfer, the electron affinity of the 3nπ* state is proved to be approximately equal to that of the 3ππ* state. However, a solvent dependence is found in the dynamic decay of TX·– anion radical. In the strongly acid aqueous acetonitrile (pH=3.0), a dynamic equilibrium between protonated and unprotonated TX is definitely observed. Once photolysis, 3TXH+* is produced, which contributes to the new band at 520 nm.