A new application of solvatochromic pyridinium-N-phenolate betaine dyes: examining the electrophilicity of lanthanide shift reagents

The well-known solvent polarity indicators, pyridinium-N-phenolate betaine dyes, appeared to be promising reactants for comparing the electrophilicity of NMR chemical shift reagents such as lanthanide(III) complexes with dipivaloylmethane [tris(2,2,6,6-tetramethylheptan-3,5-dione)]. These dyes are suitable for the UV–vis spectroscopic study of weak specific Lewis acid/base interactions in solution.