Synthesis and photonics of ketocyanine dyes, 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones and ethoxytridecamethine salts based on them

Abstract

The reactions of β-dimethylaminoacrolein aminals with 2,6-dimethyl-γ-pyrone lead to 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones, whose alkylation affords ethoxytridecamethine salts. The spectral and fluorescence properties of the synthesized compounds were studied. Their absorption spectra are unusual; along with the long-wavelength band in the visible spectral region, they contain a much more intense short-wavelength band in the near UV region. This pattern of the absorption spectra is explained in terms of the model of chromophore interaction, assuming an acute angle between the chromophore “halves” of the polyene chain of the dye molecule. The central pyran ring in the ethoxytridecamethine salts can hamper conjugation in the polymethine chain. Thermochromism of 2,6-bis(4-dimethylaminoalka-1,3-dienyl)-4H-pyran-4-ones (the long-wavelength shift of the absorption spectra on cooling of the solutions) is observed; only the long-wavelength absorption band undergoes a pronounced thermochromic shift. The introduction of methyl or phenyl substituents into the polyene chains of substituted 4H-pyranones decreases the fluorescence quantum yield.