Four new betaine dyes of the Reichardt's type featuring two tolyl substituents in different attachment (2–4) or being an analogous 1-naphthyl derivative (5) have been synthesized and described with reference to their negative solvatochromism. The dinaphthyl derivative 5 and also a corresponding intermediate nitrophenol 9d were shown with variable- temperature NMR spectroscopy to form conformational atropisomers in solution. Crystal ...
