Naphthoquinone colouring matters. Part 4. Amino-substituted 1,2-dimethylnaphth[2,3-d]imidazole-4,9-diones

Abstract

Synthetic routes to new 5- and 8-amino-substituted 1,2-dimethylnaphth[2,3-d]imidazole-4,9-dione dyes are described. The products are more hyposochromic than their 1,4-naphthoquinone counterparts, but are more bathochromic than the related 9,10-anthraquinone dyes. The bathochromic effect is enhanced by protonation or methylation of the heterocyclic ring to give the imidazolium derivatives. The PPP–SCF–MO procedure is used to interpret the visible absorption spectra of the dyes.