On Cyanine Dyes. X. Conformation of the Structures of the Tri-nuclear Cyanine Dyes

In continuation of studies of Cyanine dyes which have been prepared previously1•2>, the new method of preparation of Krypto·cyanine OA 1 (KCOA 1)> and of Thiazolocyanine OA 1 (TCOA 1) is herein described. As to the question of the structures of the trinuclear cyanine dyes, which is of interest, the ,8-methyl-trimethine · type (1)> is conceivable on basis of the formation of the tri-mesomethyl-acridylmethane tri-iodide, which was obtained by the reaction -of 9-methyl-acridine-alkyl-iodide and orthoformic acid ethylester>. In this paper I report on the new preparative methods for TCOA 1 as an additional example. The tri-nuclear dyes have been indicated to have the structure of the a-vinyl-trimethine type (II)>. The a'vinyl-trimethine type (IIIf> may be tautometric isomer of type {II). I suppose that the ,8-vinyl-trimethine type (IV)8> may be obtainable when the hydrogen of aand of a'-position are replaced by less :active radicals.