Structure and properties of new classes of coupled polymethine dyes

The structure and the energy spectra of new classes of coupled polymethines (CP) (coupled cyanines, merocyanines and oxonoles) were investigated theoretically. The CPs may be considered as being composed of two identical or two different streptopolymethine fragments or as derivatives of poly(peri-naphthylene)s. All CPs display low-energy 1So ->1S1 transitions with a high transition probability. The transition energies are comparable with those of the streptopolymethine substructures. The similarity of the energy spectra of streptopolymethines and CPs is determined by the symmetry of the frontier MOs of the streptopolymethine fragments and the CPs.