Synthesis of 3-Methylpyridocarbazolium Salts and Derived Cyanine Dyes

Article abstract of DOI:10.1007/BF00473454

When carbazole is heated with formaldehyde and acetone (or with methyl vinyl ketone) in the presence of mineral acid, 3-methylpyrido<3,2-j,k>carbazolium salts form.These react with p-dimethylaminobenzaldehyde, triethyl orthoformate, Michler's ketone, 1-ethylquinolinium iodide, or 1,3,3-trimethyl-2-formylmethyleneindolinium iodide to give the respective cyanine dyes.Deviations of the unsymmetrical dyes and Hueckel molecular orbital calculations show that the Brooker basicity of the pyrido<3,2,1-j,k>carbazolium series is lower than that of the 1-phenylquinolinium series.