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Early Events in the Photochemistry of 1,2,3-Thiadiazole Studied by Ultrafast Time-Resolved UV–Vis and IR Spectroscopies

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journal contribution
posted on 22.12.2011, 00:00 by Gotard Burdzinski, Michel Sliwa, Yunlong Zhang, Stéphanie Delbaere
Photochemistry of 4-methyl-5-carboethoxy-1,2,3-thiadiazole (MCT) in solution was studied at room temperature using UV–vis and IR transient absorption spectroscopies (λex = 266 nm). Three deactivation pathways are discussed: thiirene formation, thioketene generation, and the internal conversion by repopulating MCT in the ground state. Ultrafast techniques show a very fast rise (<0.4 ps) of thiirene species in acetonitrile, possibly as a result of a rearrangement in the singlet excited state of MCT in concert with molecular nitrogen extrusion. The remarkable stability of thiirene in solution on a millisecond time scale is limited by the process of dimerization (thiirene–thiirene, thiirene–thioketene). NMR analysis permitted identification of stable photoproducts as 1,3-dithietane, 1,3-dithiole, and thiophene derivatives.