Synthesis of novel squaraine dyes and their intermediates

We investigate the reactions of mono-substituted squaraines with CH-acidic nucleophiles, heterocyclic methylene bases and thionating reagents. The reactions of mono-substituted squaraines with malononitrile, cyano- and nitroacetic esters, barbituric acid, 1,3-indanedione, NaHS and P4S10 lead to ring-substituted mono-squaraines. These intermediates are useful for the synthesis of novel squaraine dyes with interesting photophysical properties.