Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The synthesis of N‐methyl‐benz[f]isoindole (<jats:bold>2</jats:bold>) and N‐methyl‐dibenz[e,g]isoindole (<jats:bold>3</jats:bold>) is reported. The NMR. spectra of N‐methyl‐isoindole (<jats:bold>1</jats:bold>) and of <jats:bold>2</jats:bold> have been analysed and the implications concerning the alternation of bond lengths are discussed. The photophysical properties of <jats:bold>1</jats:bold> to <jats:bold>3</jats:bold> have been investigated by the following methods: HeI photoelectron (PE.) spectroscopy, UV./VIS. absorption (polarization measurements by the stretched‐foil technique) and emission spectroscopy (fluorescence spectra, lifetimes and quantum yields, phosphorescence spectra), and flash spectroscopy (triplet‐triplet absorption spectra). The discussion of the results is based on HMO. and PPP SCF CI. calculations and points to the relationship between the heterocycles <jats:bold>1</jats:bold> to <jats:bold>3</jats:bold> and the corresponding benzenoid hydrocarbons obtained by replacement of the NMesubunit by CHCH. Some comments concerning the ground state properties of isoindole and related compounds are derived from the analysis of their electronic structure.</jats:p>