Synthesis of the first representative of dicarbothiacyanine dyes with completely fluorinated polymethine chain

2-Iodobenzothiazole was reacted with tributyl(pentafluorobutadienyl)tin in the Stille reaction conditions to give 2-pentafluorobutadienylbenzothiazole 1. The quaternary salt of 1 via interaction with 2-fluoromethylbenzothiazole methylene base, obtained in situ, forms two cyanine dyes 8 and 9 as a result of nucleophilic attack of two different positions of perfluorobutadiene chain. The pure 2-fluoromethylbenzothiazole methylene base (in a dimer form) was obtained by deprotonation of the corresponding salt by NaH and on reacting with 1 forms the dye base 11 that underwent electrocyclization and subsequent HF addition to form the cyclohexadiene 12 identified by X-ray analysis data. Upon quaternization and HF abstraction by toluidine the recyclization occurred and dye 8 – the first representative of dicarbothiacyanine dyes with perfluorinated polymethine chain – was obtained. It has λmax = 691 nm, that is 41 nm more than in non fluorinated dye, vinylene shift is equal to 111 nm.

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