Light stability of pyrazolotriazole azamethine dyes at oil/aqueous interfaces.
Film and dispersion coatings of two pyrazolotriazole azamethine (PT) dyes are used to study the effect of increasing the surface-area-to-volume (SA : V) ratio of the oil/aqueous (solvent/gelatin) interface on nonoxidative and oxidative fade characteristics. High concentration solutions of the dyes in a poly(vinyl acetate)dicyclohexylphthalate mixture as solvent are coated on glass substrates with a gelatin overcoat to produce thin film coatings and are also dispersed in gelatin to create "oil-in-gelatin" dispersion coatings. It is calculated that the dispersion coatings possess a SA : V ratio of approximately 20x greater than the film coatings. In nonoxidative fade conditions both the film and dispersion samples possess similar quantum yields of fade, implying that the presence of a solvent/gelatin interface does not significantly affect any electron transfer fade mechanisms. However, in oxidative fade conditions increasing the SA : V ratio of the interface by 20x leads to an increase in the quantum yield of fade of only a factor of 1.5-2. This disproportionate increase in the fade kinetics in dispersion coatings is explained by a kinetic scheme modelling oxygen diffusion through the coatings. It shows that the rate determining step for dye fade starts to become the diffusion of oxygen through the air/gelatin interface, and explains why changes in the SA : V ratio are not fully transferred to the quantum yield of fade.
Department of Chemistry, Imperial College, London, UK SW7 2AY. ck_parmar@yahoo.co.uk
Chetan K
CK
Parmar
Garry
G
Rumbles
Christopher J
CJ
Winscom
D004396:Coloring Agents / Q000737:chemistry*; D008027:Light; D009821:Oils / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D014867:Water / Q000737:chemistry*
D004396:Coloring Agents; D009821:Oils; D014867:Water