A general framework for the solvatochromism of pyridinium phenolate betaine dyes

► A general framework is presented for the solvatochromism of pyridinium phenolate betaine dyes. ► The three types of solvatochromism (negative, inverted and positive) are ultimately reduced to a general inverted behavior. ► The type of solvatochromism is determined by the region where this inversion should take place. ► The framework explains an 'anomalous' solvatochromic behavior of large betaines. ► Changes in the behavior of dyes, when their structures are modified, are also explained.