Facile synthesis of an ambient stable pyreno[4,5-]pyrrole monoanion and pyreno[4,5-:9,10-′]dipyrrole dianion: from serendipity to design

The stability of singly or multiply negatively charged π-conjugated organic compounds is greatly influenced by their electronic delocalization. Herein, we report a strategic methodology for isolation of a mysterious compound. The isolated compounds, a pyreno[4,5- b ]pyrrole monoanion and pyreno[4,5- b :9,10- b ′]dipyrrole dianion, were highly stable under ambient conditions due to high delocalization of the negative charge over multiple electron deficient C&z.tbd;N groups and pyrene π-scaffolds and allowed purification by column chromatography. To our knowledge, this is the first report on TCNE type reductive condensation of malononitrile involving pyrene di- and tetraone and formation of pyrenopyrrole. All compounds were characterized by spectroscopic methods and X-ray crystallography. A UV-vis spectroscopic study shows an intense low energy absorption band with a large absorption coefficient ( ). An ambient stable pyreno[4,5- b ]pyrrole monoanion and pyreno[4,5- b :9,10- b ′]dipyrrole dianion have been isolated and characterized, showing a low energy intense absorption band with the absorption coefficient reaching 7.1 × 10 4 dm 3 mol −1 cm −1 .