Cyanines are formally compounds with two nitrogen atoms linked by an odd number of methene units. 26 28 The nitrogen atoms are parts of the heterocyclic units (such as indole, benzoxazol, or benzothiazol) . The structures and optical properties of representative cyanine dyes used for in vivo imaging are presented[1]. Cyanines are characterized by long wavelength, tunable absorption and emission, very high extinction coefficient (up to 300,000 M 1 cm 1), good water solubility, and relatively straightforward synthesis[2].
