Patent ID: 7132550

Claim:
A method for preparing infrared absorbing cyanine dyes of the structure: in which: R 1 is hydrogen, or R 1 is one or more alkyl, alkoxy, carboxyl, nitro, cyano, trifluoromethyl, acyl, alkyl or aryl sulfonyl, or halogen groups, or R 1 is the atoms necessary to form a substituted or unsubstituted benzo group; R 2 is alkyl, aryl, or aralkyl; Nu is halogen, substituted or unsubstituted phenoxy, substituted or unsubstituted thiophenoxy, or substituted or unsubstituted diphenylamino; Y is O, S, NR′, or C(R′) 2 , where R′ is hydrogen or alkyl; m is zero or one; n is two, three, or four; and A is an aromatic group that has n sulfonate groups; the method comprising the steps of: a) reacting an activated methylene group containing a heterocyclic base of the structure: with a compound of the structure: and forming an intermediate in a reaction mixture; in which W is O or Ar—N, Ar is an aromatic group, X − is an anion, and m is zero or one, and b) adding a salt of A to the reaction mixture; and c) isolating the infrared absorbing cyanine dye; in which the infrared absorbing cyanine dye is the only compound isolated in the method.