Synthesis and properties of some novel pyrazolone-based heterocyclic azo disperse dyes containing a fluorosulfonyl group

A series of heteroarylazo disperse dyes derived from pyrazolones and fluorosulfonyl anilines were synthesized, and their thermal and spectral properties were investigated with respect to the effect of substituents on absorption spectra, halochromism, and solvatochromism. Heteroarylazo disperse dyes, which contain a nitro group instead of a fluorosulfonyl group para to the azo group in the diazo component, were also synthesized for comparative purpose. The fluorosulfonylarylazopyrazolone dyes had absorption maxima at shorter wavelength and showed lower extinction coefficients than the nitroarylazopyrazolone dyes. The synthesized dyes also exhibited positive halochromism and solvatochromism, so the absorption bands of the dyes moved toward longer wavelengths as the acidity or polarity of the solvent increased. 4-Fluorosulfonyl-substituted dyes generally showed lower thermal stability than their 4-nitro-substituted analogs, because the lower electron-withdrawing power in the diazo components tended to decrease the polarizability and dipole interactions.

► New arylazopyrazolone dyes containing a fluorosulfonyl group have been examined.
► The dyes showed a more hypsochromically shifted color than the nitroarylazopyrazolone dyes.
► The dyes have lower thermal stability than the nitro- analogs.
► The dyes exhibited positive halochromism and solvatochromism.
► Hydrogen bonding influenced both the spectral and thermal properties of the dyes.