Ketocyanine dyes: impact of conjugation length on optical absorption and third-order polarizabilities.

Broken symmetry and symmetry adapted cluster-configuration interaction techniques help to understand the structure-property relationships like impact of conjugation length on the electronic structure, small energy optical absorption and third-order polarizabilities in symmetric ketocyanine dyes. The sum-over-states approximation truncated to essential states model helped to understand the origin of the negative sign and the most relevant components of average static third-order polarizabilities. The results can be used as a design principle to model the ketocyanine dyes which can absorb in the visible to near-infrared region and show large negative third-order nonlinear activity.