Spectroscopic Studies on Dyes VI. Cis‐Trans Isomerism of N,N′‐Dimethyl‐5,5′, 7,7′‐Tetrabromoindigo [l a]

Abstract

AbstractThe photochemical transcis isomerization of N,N′‐dimethyl‐5,5′,7,7′‐tetrabromoindigo was studied by irradiation of a benzene solution of this dye with filtered red light (λ > 610 nm), followed by point‐by‐point determination of its spectral absorption at 10 nm intervals throughout the visible region of the spectrum. From these data it was possible to calculate the spectral absorption curve of the cis isomer. The data obtained were found to be consistent with preliminary results on N,N′‐dimethylindigo [2] and in contradiction with those of Pummerer and Marondel [3] on these dyes.