Novel asymmetric dihetarylethenes derived from N-isopropylindole and thiophene: synthesis and photochromic properties

Novel asymmetric dihetarylethenes, viz., 3-(1-isopropyl-5-methoxy-2-methyl-1H-indol-3-yl)-4-(3-thienyl)furan-2,5-dione and 1-alkyl/aryl-3-(1-isopropyl-5-methoxy-2-methyl-1H-indol-3-yl)-4-(3-thienyl)-1H-pyrrole-2,5-diones, were obtained. These dihetarylethenes exhibit photochromism in solutions. Replacement of the N-methyl group in the indole fragment by the N-isopropyl group imparts photochromic properties to the resulting furan-2,5-dione derivative. The open forms of (N-isopropylindol-3-yl)pyrrole-2,5-diones are characterized by lower quantum yields of fluorescence, and their cyclic forms are thermally more stable.