Blue sensitizing dyes: synthesis, spectroscopy and performance in photographic emulsions

The synthesis is given of 12 mostly unsymmetrical monomethine cyanine dyes containing the pyridine and/or the benzothiazole moiety. Dye structures were determined from mass spectrometric and nuclear magnetic resonance (NMR) data. In addition to providing structure information, fast atom bombardment mass spectrometry also proved an efficient method to test ionic homogeneity, and the NMR spectra provided additional information about the electron distribution in the dyes. The compounds were further characterized by elemental analysis, high-pressure liquid chromatography, and UV-visible spectroscopy. Finally, we tested the performance of the dyes as blue sensitizers in photographic T-grain emulsions (sensitivity increase and contrast).