The Comparative Solvatochromism of Arylazo and Heteroarylazo Compounds Based On N,N‐Diethyl‐m‐acetylaminoaniline and N,N‐Diethyl‐m‐toluidine

Abstract Azobenzene dyes derived from various anilines and aminothiaheterocycles azo‐coupled with commercially important N,N‐diethyl‐m‐toluidine (T series) and N,N‐diethyl‐m‐acetylaminoani‐line (A series) are positively solva‐tochromic. The visible spectra of 16 pairs of derivatives have been measured in up to 22 solvents, and the transition energies related to Kamlet‐Taft solvent polarity parameters. In general, A‐series dyes are more bathochromic than their T‐series counterparts in nonpolar solvents, consistent with colour chemistry tradition. However, in more dipolar solvents the more bathochromic T‐series representatives unexpectedly become more bathochromic than their A‐series partners. The relative solvatochromic shifts of the A and T series are related to their respective dipole moments. These in turn are distinguished by the effect of the anilide carbonyl group dipole moment, which is antiparallel to, and thus reduces, the dipole moment of the chromogen.