Five new substituted indocarbocyanine dyes with N-sulfonic acid moiety were synthesized by refluxing a selected 1-(3'-sulfopropyl)-2,3,3-trimethyl-indolenine salt with etheyl orthoformate in pyridine or acetic anhydride. In comparison with the N-alkyl partner these dyes exhibit higher melting points and higher solubility in polar solvent. Absorption maxima of these dyes are in the range 540～580nm with higher extinction coefficient (1～2×10^5L·mol^-^1·cm^-^1) .

Key words: SYNTHESIS, SENSITIZER, DYES, CYANINE DYES