Twist angle dependent mesomerism and spectroscopy in substituted anilines: Absorption and fluorescence spectra of indoline derivatives as planar model compounds

Absorption and emission spectra of 5-cyano-N-alkyl-indolines have been compared to those of the corresponding p-cyano-N,N-dialkylanilines, and the red shift and anomalously low absorption coefficient of the indolines analysed in terms of a molecules-in-molecules (MIM) model. The widely applied cos2 θ equation relating oscillator strength and intramolecular twist angle θ is shown to be inadequate for near planar geometries in this case.