Overcrowded molecules. Part XIII. Thermally stable photochromic systems involving (E)-2-isopropylidene-3-(naphthylmethylene)succinic anhydrides and N-phenylimides

Abstract

(E)-2-Isopropylidene-3-(α- or β-naphthylmethylene)succinic anhydrides and N-phenylimides undergo reversible photochemical ring closure to form orange or red 4,4a-dihydrophenanthrenes (DHPs) which are thermally stable at ambient temperature presumably because of their fused benzene rings. The potentially multiphotochromic yellow (E,E)-3,3′-di-isopropylidene-2,2′-(naphthalene-2,6-diyldimethylidyne)disuccinic bis-N-imide gives, on irradiation at 366 nm, the thermally stable red DHP. Attempts to cyclise this DHP or to detect a double ring closure of the bis-imide proved unsuccessful.