A novel general method for preparation of neutral monomethine cyanine dyes

Two novel general experimental procedures for preparation of neutral monomethine cyanine dyes without using a basic agent have been developed. The procedures allow synthesis of cyanine dyes by reaction of substituted methylthio aromatic heterocycles with different quaternized nitrogen containing heterocycles by simple melting or by their reaction in acetic anhydride for short reaction times. The proposed method is very versatile as a variety of different starting materials can be used.