Synthesis and physical performance of indole and benzimidazole cyanine dyes

Nine indole and benzimidazole cyanine dyes, used as green-sensitizing dyes in photographic emulsions, are synthesized. The compounds are characterized from mass spectrometric and NMR spectroscopic data, and elemental analysis. FAB mass spectrometry proved to be an efficient method for determining the structure of the compounds. From UV–VIS data of the compounds the sensitizing properties of the cyanine dyes are predicted. The reflection spectrum of Gs2-9 coated in photographic emulsions showed J-aggregation behaviour at λ= 560 nm. Unsymmetric benzimidazole–indole cyanine dyes showed good to excellent green sensitizing properties in photographic emulsions, whereas symmetric indole cyanine dyes showed heavy residual colour and no sensitizing properties.