The photochemical behaviour of 6-X-4H-3(bicyclo[2.2.1]-5-heptene-2,3-dicarboximidoiminomethyl)-4-chromones. Photochromism and thermochromism

Abstract

The photochemical behaviour of 6-X-4H-3(bicyclo[2.2.1]-5-heptene-2,3-dicarboimidoximinomethyl)-4-chromones (X=CH3, Cl, NO2) was studied upon irradiation (λirr≅310 nm) in CH3OH and benzene. Direct E-Z or Z-E photoisomerization and thermal Z-E isomerization were observed. The activation energies of Z-E isomerization were in the range 8.7-69.5 kJ mol-1. Prolongation of the irradiation of the title compounds till the equilibrium is reached between E and Z isomers results in the irreversible process. The products of this irreversible process were identified. Fluorescence emission and excitation spectra were measured. © 2000 Elsevier Science S.A. All rights reserved.