Ketohydrazone dyes derived from 4-morpholino-2-naphthol and ortho-substituted anilines: Further examination of the hyperchromism induced by the 4-morpholino-2-naphthol moiety

A series of ketohydrazone dyes has been synthesised from 4-morpholino-2-naphthol and ortho-substituted anilines by conventional diazotisation coupling chemistry. Whilst the new, dull orange-red, dyes exhibit only a minor variation of absorption maxima across the range of substituents, they are hyperchromic relative to Sudan 1 and their none ortho-substituted analogue. Protonation of selected dye examples results in a bathochromic and hyperchromic shift in absorption maxima to afford vibrant purple-coloured protonated species.