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 caus ed on the absorption region of symmetric polymethine dyes by a cyclic fragm ent of the C-2v symmetry incorporated in their main chromophore. In the con text of the Green's function formalism, relationships between the structure of a dye molecule (represented by additive topological parameters of end g roups, bridge, and the polymethine chain) and bridge-induced shifts of abso rption maxima are derived. The trends revealed in signs and magnitudes of t he absorption shifts are exemplified by treatment of squaraine and thiosqua raine molecules. (C) 1999 Elsevier Science Ltd. All rights reserved.