Comparisons between azo dyes and Schiff bases having the same benzothiazole/phenol skeleton: Syntheses, crystal structures and spectroscopic properties

Three pairs of heterocyclic azo dyes and their corresponding Schiff bases were prepared by diazotization and Schiff-base condensation reactions between substituted 2-aminobenzothiazoles and either 3-(diethylamino)phenol or 3,5-dichloro-2-hydroxybenzaldehyde in order to obtain some high performance Disperse Red dyes and compare the structural and spectral differences between the azo dyes and Schiff bases. All azo dyes and Schiff bases in this work have the same benzothiazole/phenol skeleton but different substituent group in the phenyl ring. X-ray single-crystal diffraction analyses of selected compounds reveal that they have a similar planar conformation between the benzothiazole and phenol units but dissimilar dimeric crystal packing. Electronic spectra of the dyes demonstrate that the presence of NN and CN double bond chromophore units as well as substituent effects of different auxochrome groups in the benzothiazole backbone leads to significant alterations of bathochromic and hypsochromic shifts despite only slight differences in their molecular structures.

Three heterocyclic azo dyes and their corresponding Schiff bases having a common benzothiazole/phenol skeleton but different substituent groups have been synthesized and structurally and spectroscopically characterized and compared.Figure optionsDownload as PowerPoint slideHighlights
► Three pairs of heterocyclic azo dyes and Schiff bases are synthesized and characterized.
► They have the same benzothiazole/phenol skeleton but different substituents.
► Comparisons are made on their molecular and electronic structures, spectroscopy and band gaps.