Chapter 15 - Cyanine dyes and related compounds

Abstract

Publisher Summary This chapter focuses on the chemistry of cyanine dyes. The most important progress in the application of cyanine dyes is in laser physics, nonlinear optics, optical data storage, liquid crystal displays (LCD's), dye sensor techniques, initiating photopolymerization, photochromism, electrochromism, electrophotography, phototherapy, as well as in fluorescence labeling in analytical chemistry, DNA sequencing, immunoassay techniques, and for the determination of membrane potentials. The chapter reviews the theory of color and constitution, the syntheses of cyanine dyes, the properties of cyanine dyes, and the applications of cyanine dyes. The properties of cyanines and related compounds are mainly governed by the unique features of the ideal polymethine state, that is, full bond lengths equalization and zero bond order alternation (BOA), respectively, combined with strong alternation of the л-electron densities through the polymethine chain. There are linear relationships between the energy of the highest occupied molecular orbital (HOMO) of cyanine dyes, accessible by quantum chemical calculations, and their anodic halfwave potential, as well as between the dyes' energy of their lowest unoccupied molecular orbital (LUMO) and their cathodic halfwave potential. The energy levels are also related to the cyanine dyes' susceptibility for spectral sensitization and desensitization in photoinduced electron transfer reactions.