A simple treatment of bridge-induced shifts of absorption for symmetric polymethine dyes with a bridged chromophore

A simple topological model is developed which accounts for the effects caused on the absorption region of symmetric polymethine dyes by a cyclic fragment of the C2v symmetry incorporated in their main chromophore. In the context of the Greenʹs function formalism, relationships between the structure of a dye molecule (represented by additive topological parameters of end groups, bridge, and the polymethine chain) and bridge-induced shifts of absorption maxima are derived. The trends revealed in signs and magnitudes of the absorption shifts are exemplified by treatment of squaraine and thiosquaraine molecules.