Intermediates of photolysis of 1,3,2,4-benzodithiadiazines studied by matrix isolation spectroscopy and quantum chemistry

Photolysis of 12π-electron, formally antiaromatic, 1,3,2,4-benzodithiadiazine (1a) and its tetrafluoro-substituted derivative (1b) was studied in glassy matrices at 77 K and in an argon matrix at 14 K by UV, IR, and ESR spectroscopy. In these matrices, a diamagnetic species (3a,b) is formed as a persistent species. It is product of the intramolecular transformations of heterocycles 1a,b and the precursor of 1,2,3-benzodithiazolyl radicals (2a,b). The nitrenoid structure, intermediate between the structures of singlet 1,2,3-benzodithiazol-2-ylnitrene RS—N: and the corresponding thiazyl RS≡N, was ascribed to intermediate 3a,b in agreement with the data of IR spectroscopy.