Solvent-induced E/Z(C=N)-isomerization of imines of some hydroxy-substituted formylcoumarins

Aromatic imines, namely, 5-formyl-6-hydroxy-4-methyl- and 8-formyl-7-hydroxy-4-methylcoumarin derivatives, have been synthesized. A dependence of their spectral characteristics (1H NMR spectra, electronic absorption spectra) from the solvent (DMSO, CHCl3, DMF, acetonitrile, MeOH) has been studied. The solvatochromic effects observed for a number of imines, first of all, for 7-hydroxy-4-methyl-8-(4′-nitrophenylimino)methyl-2H-1-benzopyran-2-one, were related to their E/Z-isomerization with respect to the C=N bond based on the quantum chemical calculations by the AM1, PM3, PPP CI methods.