On the Absorption Spectrum of Some Polymethine Dyes

Abstract

The energy levels of certain polymethine dyes are calculated approximately. The dyes consist of a chain of conjugated double bonds, with end groups which might or might not differ from each other. Ions and neutral molecules are treated. The calculations are performed both with the valence bond method (resonance between different structures) and the LCAO method, but without antisymmetrization and without taking electronic interaction into account. The effect of chain length and of the nature of the end groups is discussed.