This invention relates to improved imaging systems based on the formation of yellow colored coordination compounds of transition metals with certain ligands. The formation of colored coordination compounds can be employed to generate images and is important in the manufacture and use of pressure sensitive transfer papers for preparing carbonless copies. In particular, this invention relates to certain ethanediimidic acid bis[(arylalkylidene)hydrazide] compounds, and particularly to certain ethanediimidic acid bis[( o -hydroxyarylalkylidene)hydrazide] compounds, to their coordination compounds with certain transition metals, and to their use in pressure sensitive carbonless copy paper systems. These compounds have been found to provide excellent yellow colors when used in pressure sensitive carbonless copy-papers wherein the image is formed by the reaction of a color-forming compound with transition metal salts such as those of nickel, cobalt, iron, copper, and similar materials. These yellow color-formers have the advantage of greater solubility in encapsulation solvents and lower volatility than previously used yellow color-formers.
The invention also concerns the admixture of these certain color-formers with N-(monosubstituted)dithiooxamides and/or N,N′-(disubstituted)dithiooxamides to form images of various colors and preferably black images during the application of appropriate pressure to pressure sensitive imaging constructions such as carbonless paper constructions.