A method to make squaraine dyes involves the reaction of 1,8-diaminonaphthalene with 1,3-dihydroxyacetone dimer in a first reaction mixture comprising the appropriate solvents to prepare a first intermediate. This first intermediate is then reacted with an organic acylating agent in the presence of a suitable solvent to form a second intermediate. Lastly, after isolation, the second intermediate is reacted with squaric acid in a particular hydroxylic solvent/nonpolar solvent mixture that dissolves squaric acid and forms a ternary azeotrope with water and the water is at least partially removed. The resulting dyes have the following general structure wherein R is an organic radical derived from the organic acylating agent.
Method of making dihydroperimidine squaraine compounds