The effect of annelation on the absorption spectra of polyazo dyes

Abstract

The effects of annelation on the absorption spectra of polyazo dyes are discussed on the basis of the PPP MO method. Large bathochromic shifts (15–80 nm) of Λ max were observed if the 1, 4‐phenylene ring in the conjugating bridge of polyazo dyes was replaced with a 1, 4‐naphthylene ring (annelation). The annelation effect on Λ max was increased as the strength of acceptor group increased in disazo dyes with an intramolecular charge‐transfer chromophore. The additive properties of Λ max were observed in a number of annelated trisazo dyes, which were confirmed by the PPP MO method. Steric effects were observed in trisazo dyes derived from N‐alkylnaphthylamine. The solubility of dichroic polyazo dyes in liquid crystals was generally improved, but their dichroic properties were only slightly affected by annelation.7