Cationic 3H-indolium dyes by ring-opening of benzo[l,3]oxazine

摘要

The reaction of 2-methylbenzo[1,3]oxazine with (hetero)aromatic aldehydes under acid catalysis afforded directly polymethine dyes, formed by a thermal ring-opening of the oxazine cycle followed by condensation with the aldehydes. These dyes have the structure of a cationic thermally stable coloured open form of a photochromic benzo[1,3]oxazine and do not undergo ring-closure to afford the closed form again, even under basic treatment. All of the dyes showed reversible acidochromic properties.