Novel Dimethinemerocyanine Dyes with the (Snlfobutyl)henzothiazole Group as Donor Part of the Chromophor and their Aggregation Tendency in Aqueous Solution
A series of novel dimethinemerocyanine dyes with the (sulfobuty1)benzothiazole group as the donor part of the chromophor is synthesized in good yield and their aggregation tendency in HzO without addition of salt investigated. The merocyanine dye 2b only gives J-aggregation in HzO. The dyes la-f and 2a exhibit an intense, red-shifted absorption band due to J-aggregation in H,O in the presence ofMe4NC1. In contrast, the dyes l g and 2c--f show a slightly red-shifted absorption band. The degree of aggregation in HzO is investigated by ultracentrifugation of the representative 2e. Indeed, the slightly red-shifted absorption band in H,O 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/H,O 1.3. The dye 11 shows an absorption band in H,O that is probably blue-shifted because of negative solvatochromism. The merocyanine dye 13 gives H-aggregation in H20. ' ) Die Autoren danken Herrn A. Lustig, Biozentrum der Universitit Basel, Abt. Biophysikalische Chemie, Klingelbergstrasse 70, CH-4056 Basel, fur die Ultrazentrifugationsstudien und deren Interpretation [28].