A theoretical study of the electronic spectra of the benzazulenes and benzologue-tropylium cations and a critical examination of the perimeter model

The electronic spectra of the benzazulenes and benzologue-tropylium cations have been interpreted on the basis of a perimeter model, using a modified form of the Pople-Pariser-Parr method. The agreement between theory and experiment is satisfactory, and much better than when the same method is applied to benzenoid hydrocarbons. A critical discussion is given of the use of the perimeter model for classifying the states of these compounds.