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

Abstract

A series of novel photo- and ionochromic N-acylated 2-(aminomethylene)benzo[b]thiophene-3(2Н)-ones with a terminal phenanthroline receptor substituent was synthesized. Upon irradiation in acetonitrile or DMSO with light of 436 nm, they underwent Z-E isomerization of the C=C bond, followed by very fast N→O migration of the acyl group and the formation of nonemissive O-acylated isomers. These isomers were isolated preparatively and fully characterized by IR, ¹H, and ¹³C NMR spectroscopy as well as HRMS and XRD methods. The reverse thermal reaction was catalyzed by protonic acids. N-Acylated compounds exclusively with Fe²⁺ formed nonfluorescent complexes with a contrast naked-eye effect: a color change of the solutions from yellow to dark orange. Subsequent selective interaction with AcO^- led to the restoration of the initial absorption and emission properties. Thus, the obtained compounds represent dual-mode "on-off-on" switches of optical and fluorescent properties under sequential exposure to light and H⁺ or sequential addition of Fe²⁺ and AcO^- ions.

Keywords: N→O acyl rearrangement; fluorescence; molecular switches; naked eye effect; photochromism.