Sedigheh Hashemnia

Cyanine (polymethine) dyes belong to a group of organic compounds which have a large conjugated p-system. A typical polymethine dye molecule consists of 2 nitrogencontaining heterocycles connected by an unsaturated carbon chain, the polymethine chain. Polymethine dyes are usually divided into mono-, di-, tri-, tetra-, penta- and hepta-methine dyes according to the length of the chain. The dyes are used in photography, 1 photodynamic therapy,2 proteomics,3 and biomolecular labeling.4–8 Polymethine dyes are also highly fluorescent and they absorb and emit light mostly in the visible region of the optical spectrum, as a function of the chain length