Neue Dimethinmerocyanin‐Farbstoffe mit der (Sulfobutyl)benzothiazol‐Gruppe als Donor‐Teilchromophor und deren Aggregationsverhalten in wässriger Lösung

Abstract

Novel Dimethinemerocyanine Dyes with the (Sulfobutyl)benzothiazole Group as Donor Part of the Chromophor and their Aggregation Tendency in Aqueous SolutionA series of novel dimethinemerocyanine dyes with the (sulfobutyl)benzothiazole group as the donor part of the chromophor is synthesized in good yield and their aggregation tendency in H2O without addition of salt investigated. The merocyanine dye 2b only gives J‐aggregation in H2O. The dyes 1a–f and 2a exhibit an intense, red‐shifted absorption band due to J‐aggregation in H2O in the presence of Me4NCl. In contrast, the dyes 1g and 2c–f show a slightly red‐shifted absorption band. The degree of aggregation in H2O is investigated by ultracentrifugation of the representative 2e. Indeed, the slightly red‐shifted absorption band in H2O is due to aggregation of ‘oligomers’ of the dye. Contrary to the aggregation of ‘polymers’ of dyes (J‐aggregation), we suggest the term ‘K’ band for the slightly red‐shifted absorption band. The hemicyanine dye 5 gives the same absorption band in MeOH and in MeOH/H2O 1:3. The dye 11 shows an absorption band in H2O that is probably blue‐shifted because of negative solvatochromism. The merocyanine dye 13 gives H‐aggregation in H2O.