Its 2- and 4-methyl derivatives are precursors to cyanine dyes. Other historically common fluorophores are derivatives of rhodamine (TRITC), coumarin, and cyanine. Later, when applying the model to cyanine dyes he observed a quantitative agreement with experiment. The most well-known group of methine dyes are the cationic cyanine dyes. Dyes used in DVD-Rs and CD-Rs include Phthalocyanine (greenish) Cyanine (blue) and Azo (dark blue). Indocyanine green (ICG) is a cyanine dye used in medical diagnostics. SYBR Safe is a cyanine dye used as a nucleic acid stain in molecular biology. Cyanine is the non-systematic name of a synthetic dye family belonging to polymethine group.