AZO PIGMENTS AND THEIR INTERMEDIATES - A NEW CLASS OF COUPLERS FOR RED AND NEAR-IR SENSITIVE PHOTOGENERATING AZO PIGMENTS

The synthesis of azoic couplers, 2,8-dihydroxy-3-naphthanilide and its derivatives, by first converting 2,8-dihydroxy-3-naphthoic acid into its phenyl ester followed by considering the phenyl ester with an anil ine derivative, is reported. Photogenerating bisazo and trisazo pigmen ts have been prepared by coupling 2,8-dihydroxy-3-naphthanilide with 2 ,7-diamino fluorenone and tris (p-aminophenyl)amine, respectively. The absorption spectra of these pigments are found to be red-shifted rela tive to analogous pigments synthesized from 2-hydroxy-3-naphthanilide. The data suggest that 2,8-dihydroxy-3-naphthanilides are new coupler components for red and near-IR absorbing photogenerating azo pigments. Evidence is provided that the red shift is a result of an intramolecu lar H-bonding between the 8-OH group in the coupler moiety and the nit rogen atom in the hydrazone unit of the pigment. Comparison of the pig ments synthesized in this work with those from 2-hydroxy-11H-benzo(a) carbazole-3-carboxanilides suggests that the wavelength extension achi eved by carbazole-couplers may also be a H-bonding effect, between the N-H group in the carbazole ring and the nitrogen in the hydrazone uni t. The advantage of using the couplers described in this work for prep aring red and near-IR absorbing photogenerating pigments is discussed.