Absorption Spectra of Dyes. VII. Some Steric Effects and Auxochrome-Effects on Complex Formation

Abstract

Abstract 1. The absorption spectra of the dyes prepared by coupling disazotized 2S-, H-, chromotropic, NW-, γ- and J- acid with dianisidine, and of their copper derivatives were observed in aqueous solutions of the binary mixture with Chrysophenine G, and were compared with the sum curves of the component absorption spectra. 2. The order of the equilibrium constants for a 1:1 complex formed between the dyes not containing copper and Chrysophenine G was parallel to the respective values of the difference in wave number (Δν cm−1) between maximum positions in the region of 390∼420 mμ of the curve simply added and that observed with the equimolar binary mixture of about 1×10−5mol./1.; it was also parallel to those of the decreasing ratio in optical density (ΔD⁄D) of the mixed system at the first maximum position of the sum curve. 3. Under the same conditions as above, Δν and ΔD⁄D were also determined for the mixture of the copper derivatives and Chrysophenine G. In this case, the copper derivatives of 2S-, H-, and chromotropic acid, in the presence of effective auxochromes, still revealed large values of Δν (ca. 1000 cm−1) and ΔD⁄D (ca. 15%), while the values for the rest of the derivatives were almost zero. 4. Discussing the above results, it was shown that in order to display a spectral change due to the formation of a 1:1 complex in a binary mixture with Chrysophenine G, it is necessary that the partner dye has effective auxochromes (amino, hydroxyl) as terminal groups of a conjugated system. It was also shown that the sulfonic groups which are attached to the terminal naphthalene nuclei act on the structure of the dye itself as a steric factor rather than as an electric effect (repulsion) between the ionic charges in the groups and those of Chrysophenine G, and that the more planar structure, resulting in a smaller steric effect, produces more complex.