Characterization of the Triplet State of Tanshinone IIA and its Reactivity by Laser Flash Photolysis

Tanshinone IIA (Tan IIA) has the properties of cardiovascular protection, anti-inflammation, antioxidation and anticancer. Its light-induced instability has drawn our interests in its photochemistry. Therefore, laser flash photolysis herein was used to investigate the transient photochemistry of Tan IIA. Our results show that direct photoexcitation by 355nm laser pulses or photosensitization by energy transfer can lead to the formation of the triplet state of Tan IIA ((3)Tan IIA*). The triplet absorption spectrum and molar absorption coefficient, and ISC quantum yield were determined. Self-quenching of (3)Tan IIA* by its ground state was identified as an autooxidation reaction. (3)Tan IIA* was proved to react quickly with N, N-dimethylaniline, tert-butylhydroquinone and propyl gallate via electron transfer with the diffusion-controlled rate constants. One of the products with maximum absorption around 390nm was assigned to the radical anion of Tan IIA. Our results indicate that (3)Tan IIA* is a reactive transient species and can be generated by photosensitization or direct photoexcitation. According to our results, the possible role of Tan IIA as a photosensitizer to induce potential phototoxicity via Type-II pathway in the presence of O-2 can be predicted.