Neue Sulfobutyl‐haltige Bis(dimethinmerocyanin)‐Farbstoffe mit isolierten Chromophoren im Molekül und deren Aggregationsverhalten in wässeriger Lösung

Novel Bis(dimethinemerocyanine) Dyes with Isolated Chromophores in the Molecule Containing the Sulfobutyl Group and their Aggregation Tendency in Aqueous Solution The bis(dimethinemerocyanine) dyes 7a–c with Chromophores separated by a polymethylene chain as ‘isolator’ are synthesized in good yield. Their aggregation tendency in organic solvents, organic solvents/H2O mixtures, and in H2O is investigated. In organic solvents, the dyes 7a–b show a splitted absorption band, due to interaction of the two Chromophores of the dye. In H2O, 7a exhibits an intense absorption band at 496 nm (ϵ = 224 300 1·mol−1·cm−1) with a small width \documentclass{article}\pagestyle{empty}\begin{document}$ (\tilde v_{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} = 1000\;{\rm cm}^{ - 1}) $\end{document} and shoulders at 552 and 580 nm. In presence of starch, this absorption band shifts to 617 nm, probably due to J‐aggregation. The dye 7b shows the same spectral behaviour as 7a. In contrast, 7c exhibits an absorption band without splitting in organic solvents; the interaction of the Chromophores has disappeared. In H2O and in H2O containing starch, 7c shows a wide absorption band, due to interaction of the Chromophores of the dye.