Deactivation of the first excited singlet state of thiophenols.
On the bases of picosecond and nanosecond laser flash photolysis with detection by emission and absorption spectroscopy, a quantitative description is given of all deactivation channels of the first excited singlet state of thiophenols ArSH(S(1)) such as fluorescence, intersystem crossing (ISC), chemical dissociation into radicals, and radiation-less internal conversion (IC). For this purpose, the photolysis of thiophenol and its methyl-, methoxy-, and chloro-substituted derivatives was studied in solvents of increasing polarity: 1-chlorobutane, ethanol, and acetonitrile. The fluorescence lifetime of the thiophenols was found to range from some hundreds of picoseconds up to a few nanoseconds, correlating with fluorescence quantum yields between 0.001-0.040, at room temperature. Depending on the substitution pattern of the aromatic ring, the quantum yield of the S-H bond dissociation was found to be between 0.3-0.5, irrespective of the solvent polarity. In laser photolysis, no triplet formation of the investigated compounds could be observed neither by the direct way nor by subsequent sensitization with beta-carotene. As a difference to the total, the radiation-less internal conversion (Phi(IC)>or= 0.5) was found to be the dominating process.
Riyad
Yasser M
YM
University of Leipzig, Interdisciplinary Group Time-Resolved Spectroscopy, Permoserstr. 15, D-4303, Leipzig, Germany.
Naumov
Sergej
S
Hermann
Ralf
R
Brede
Ortwin
O
D000975:Antioxidants / Q000737:chemistry; D007700:Kinetics; D007834:Lasers; D010636:Phenols / Q000737:chemistry*; D010782:Photolysis; D026082:Singlet Oxygen; D013050:Spectrometry, Fluorescence; D013438:Sulfhydryl Compounds / Q000737:chemistry*
D000975:Antioxidants; D010636:Phenols; D013438:Sulfhydryl Compounds; D026082:Singlet Oxygen; C042983:thiophenol