Unusual π-electron conjugation in the pyrene series

The phosphorescence spectra of naphthopyrene 7 and dinaphthopyrene 8, measured at 77 K in organic glasses and at 4.2 K in Shpolskii matrices, are reported. Contrary to expectation, the extension of the π-electron system in 8 relative to 7 produces a small violet rather than a big red shift of the phosphorescence bands. This finding is shown to be fully consistent with the sextet formalism and indicates an interruption of electronic conjugation in 8.