Photochromic systems. Part 1. Photochemical studies on (E)-2-isopropylidene-3-[1-(3,4,5-trimethoxyphenyl)ethylidene]succinic anhydride and related compounds

Abstract

The title compound photocyclises to a deep blue solvatochromic 1,8a-dihydronaphthalene (1,8a-DHN), which undergoes a thermal 1,5-H shift to yield a colourless 1,2-DHN, in addition to thermal ring-opening. The rates of these competitive reactions have been determined by measuring the thermal fade rate of the corresponding 5,8a-dideuterio-1,8a-DHN, which does not show a thermal 1,5-D shift at ambient temperatures but only a photochemical 1,7-D shift. Its thermal fade is due solely to ring-opening. The corresponding imides show similar photochromic properties. An explanation is offered for the loss or the substantial reduction of photochromic properties in ortho or para substituted alkoxyphenylmethylene(substituted methylene)succinic anhydrides and imides.