ELECTRONIC-PROPERTIES OF POLYMETHINE SYSTEMS .3. POLYMETHINE AND QUASI-LOCAL ELECTRON TRANSITIONS

The nature of the first and the higher electron transitions in linear polymethine systems containing complex conjugated terminal groups are discussed. For determination of the electron transition localization, diagrams of electron density changes on excitation and the values of the atomic localities are used It is shown that the first transition of normal polymethines is localized within the polymethine chromophore; higher transitions are associated with excitation within local chromophores. In contrast, in polyenes and polymethines containing deeply coloured nuclei, inversion of the polymethine and quasi-local transitions occurs.