Synthesis, Photophysical Properties, and Aromaticity of Pyrazine-Fused Tetrazapentalenes

Pyrazine-fused 1,2,6,6a-tetrazapentalenes
(PyTeAP) are zwitterionic
tricyclic compounds exhibiting an original pattern with four consecutive
nitrogen atoms. They were obtained by a challenging cyclization through
the formation of a N–N bond under thermolytic conditions. Ten
derivatives were synthesized, and the original scaffold of PyTeAP
was confirmed by single-crystal X-ray diffraction analysis of one
derivative. Examination of their photophysical properties in solution
revealed blue fluorescence with λem = 416–426
nm. Theoretical investigations of the aromaticity in these compounds
through magnetic criteria evidenced the presence of a dominant 14-electron
circuit at the periphery.