Synthesis, Characterization and Cation-Induced Isomerization of Photochromic Calix[4](aza)crown-Indolospiropyran Conjugates

Overview & Synopsis

Calix[4](aza)crown-5, -6 and -7 ionophores in cone and 1,3-alt conformation carrying photochromic indolospirobenzopyran (SP) signalling group were synthesized and their cation-induced isomerization to the colored merocyanine (Mc) form was studied by UV/vis spectroscopy in the presence of mono-and divalent metal ions. Under dark conditions the SP-Mc equilibrium was remarkably shifted to the colored Mc form by cations of high positive charge density (alkaline earth metal ions), and it was affected by some transition metal ions (Cu2+, Zn2+ and Pb2+) as well. Generally, the extent of isomerization of the cone conformers was larger than that of the 1,3-alt counterparts. The chelation-induced reaction was evaluated by calculating the rate constants of the coloration process.