On the solvatochromic reversal of merocyanine dyes. Part 1. The UV–VIS spectroscopic behaviour of vinylogous γ-pyridones
A theoretical approach is described to rationalize and predict the solvatochromic behaviour of vinylogous γ-pyridones. The theoretical curves obtained are shown to reproduce the experimental UV–VIS spectroscopic behaviour of dyes 1, 2, 3 and 5. The model reconciles previous conflicting reports on the solvatochromism of these and related dyes.