Synthesis and properties of benzobis(thiadiazole)s with nonclassical pi-electron ring systems

Benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole) containing a hypervalent sulfur atom has a low LUMO energy. The aryl derivatives were synthesized using a Stille coupling reaction, The selenadiazole analogues were also prepared. The electron accepting properties of these nonclassical heterocycles were shown by their high reduction potentials. Introduction of electron-donating groups into the electron-withdrawing heterocycles afforded novel donor-acceptor compounds. Their cyclic voltammograms showed that they are easily both oxidized and reduced. Some of them have the absorption maxima above 700 nm due to the small HOMO-LUMO separation. X-ray structure analysis of the diphenyl derivative revealed the formation of a tape-like network through short S...N contacts. (C) 1997 Elsevier Science Ltd.