Chapter 15 - Cyanine dyes and related compounds

Abstract

This chapter provides an overview of preparation methods and properties of cyanine dyes, and related compounds. The polymethine state is associated with intense light absorption at long wavelengths and with an alternation of π -charge density distribution along the chain. On excitation, the charge density distribution is reversed. The alternation of π -charge leads to a rehybridization of the σ -electron system of individual atoms to different degrees and cause an alternation in bond angles. On excitation of the molecule by light the change in the alternation of charge density also leads to a change in the bond angles and the molecule will bend. The very long chain trideca- and pentadeca-methine dyes are obtained by reaction between the appropriate heterocyclic quaternary salt and the bis-di- N -alkylanil salts from undecatetraenedial and tridecapentaenedial respectively. The condensations are effected in acetic anhydride in the presence of a tertiary aliphatic amine at a low temperature.