Photochromic 2-(N-acyl-N-arylaminomethylene)benzo[b]thiophene-3(2H)-ones with fluorescent labels and/or crown-ether receptors

Novel N-acylaminovinyl ketones of the benzo[b] thiophene series (AAB) capable of molecular switching of fluorescence or complexation with metal ions have been synthesized and their photochromic behavior studied using UV-Vis absorption/emission and H-1-/Li-7-NMR spectroscopy. Under UV irradiation the AAB compounds 2a-c containing fluorescent labels as their N-aryl substituents undergo Z/E-photo-isomerization and N-->O acyl rearrangement resulting in the formation of O-acyl isomers 3a-c. The photo-switching of fluorescence has been found in the 4-fluorenonyl derivative 2a. The benzo-15-crown-5-containing AAB 2d, e are also susceptible to the same type of photo-initiated rearrangement. The corresponding O-acyl isomers 3d-e represent a group of chemosensors which readily form stable complexes with alkali- and alkali-earth-metal cations. The AAB 2d exhibits specific selectivity for Li+ ion in the presence of Na+, K+ and Cs+.