Synthesis of photo- and ionochromic N-acylated 2-aminomethylenebenzo[b]thiophene-3(2Н)-ones with a terminal phenanthroline group

A series of N -acylated 2-aminomethylenebenzo[ b ]thiophene-3(2 Н )-ones with a terminal phenanthroline receptor substituent was synthesized. Upon irradiation in CH 3 CN or DMSO with light of 436 nm, they undergo Z/E isomerization around the C=C bond followed by rapid N→O migration of the acyl group and the formation of non-emissive O -acylated isomers. These isomers were separated preparatively and fully characterized by IR, 1 H, 13 C NMR, HRMS and XRD methods. The reverse thermal reaction is catalyzed by protonic acids. N -Acylated compounds exclusively with Fe 2+ ions form non-fluorescent complexes with a contrast naked eye effect - color change of the solutions from yellow to pink-crimson. Subsequent selective interaction with acetate anions leads to the restoration of the initial absorption and emission spectra. Thus, the obtained compounds represent dual-mode “on-off-on” switches of optical and fluorescent properties under sequential exposure to light/H + or sequential addition of Fe 2+ /AcO - ions.