Syntheses, spectral properties and photostabilities of novel water-soluble near-infrared cyanine dyes

To develop long wavelength cyanine dyes with good water solubility and high photostability for biological application, a series of heptamethine 5-sulfo-3H-indocyanine dyes were synthesized and characterized. The absorption and fluorescence spectra of the dyes in various solvents are presented, the maximum absorption and emission wavelengths ranging from 680 to 830 nm. The photostabilities are influenced by the different substitutes of the dyes: N-benzyl on the nitrogen atom at the 3H-indole ring provides better photostability than N-ethyl, the substitution of chloro group of chlorocyclohexenyl bridge in heptamethine chain with electron-donor group (such as 4-methoxylanilino) could greatly improve the photostability. In addition, the photofading is more rapid in water than in alcohol and the mechanisms are discussed.