Herstellung, Struktur und Eigenschaften neuartiger kettensubstituierter und chiraler Trimethincyanin‐Farbstoffe mit Indolin‐Endgruppen 1)

Synthesis, Structure, and Properties of Novel Chain‐Substituted and Chiral Trimethine Cyanine Dyes with Indoline End Groups Synthesis and spectroscopic properties of the trimethine cyanine dyes 3, 8a, b , and 13a, b as well as 14a‐c with new substitution patterns are described. Constitutions and configurations of 3, 8a, b and 14c have been determined by X‐ray analyses (Figures 1, 2, and 6). Dye 3 exists in the previously unknown di‐cis ( E, E, Z, Z ) configuration along the methine chain. Attempts to prepare 3 in a base‐catalysed reaction unexpectedly led to the rearranged trimethine cyanine dyes 8a, b with a centre of chirality in one of the indoline end groups. Using this Wagner‐Meerwein rearrangement after resolution, the chiral heterocyclic quaternary salts ( S )‐ 12a‐ c have been prepared, from which the optically active trimethine cyanine dyes ( S,S )‐ 14a‐c have been obtained for the first time. The UV/VIS spectra of 3, 8a and 13a (Figure 7) as well as the CD spectra of 12a and 14a (Figures 3 and 4) are compared and discussed.