Synthesis of Novel Iono- and Photochromic Spiropyrans Derived from 6,7-Dihydroxy-8-Formyl-4-Methyl-2H-Chromene-2-One

Figure 4

Continuous variation plot of the (4a)/Mg²⁺  ([4a]+[Mg²⁺]=5×10⁻⁵ M) in acetonitrile.