POLYMETHYLENE DYES FROM 2-METHYLINDOLO(3,2-B)THIAZOLO(5,4-D)QUINOXALINES HAVING SUBSTITUENTS AT THE NITROGEN ATOM OF THE INDOLE RING

Анотація

Condensation of isatin with N-methylisatin, N-ethyl, N-propyl, N-butyl, N-phenyl, N-benzoyl and 5-nitroisatin with 2-methyl 5,6-diami­nobenzthiazole gave 2-methyl-indolo(3,2-b)thiazolo(5,4-d)quinoxalines with a substituted nitrogen atom in the indole ring. When they are heated with alkyltosylates, quaternary salts are formed from which various cyanine dyes are synthesized: styryls, monomethinecyani­nes, asymmetric carbocyanines. The absorption maxima of each dye were determined and analyzed, and the results of elemental analysis for Carbon, Hydrogen, and Sulfur were given. The influence of substituents at the nitrogen of the indole ring on the absorption maxima of the synthesized dyes was established. During the transition from methyl to ethyl and further to propyl, butyl, phenyl, and benzoyl, a bathochromic shift of the absorption maximum of the dye is observed by several nanometers (for styrenes 2–6 nm, for monomethinecyanines 1–10 nm and asymmetric carbocyanines 2–7 nm) of the next dye compared to the previous one. The greatest influence of the absorption maxima bathochromic shift of dyes (up to 7 nm) belongs to N-substituents in the phenyl indole ring, benzoyl, and nitro group. The absorption maxima of the obtained cyanine dyes in an acidic environment show a strong bathochromic shift (up to 93 nm) compared to neutral solutions, which can be explained by an increase in the conjugation chain due to the one protonation of the phenazine cycle nitrogen atoms. It can be seen that N-phenyl, N-benzoyl, and the nitro group in the 5-position of the indole ring give the largest bathochromic shift from the analysis of the dyes absorption maxima. Thus, in the presence of phenyl and benzoyl in the indole ring, the absorption maxima are 456 and 460 nm, respectively, against the unsubstituted nitrogen atom in the indole ring at 440 nm.