and R2 or R3 and R4 is an aryl group, having an aryl ring substituted with an X oxy- group which forms an unstable oxide intermediate 1,2-dioxetane compound when triggered to remove X by an activating agent selected from acids, bases, salts, enzymes, inorganic and organic catalysts and electron donors so that the unstable 1,2-dioxetane compound decomposes and releases electronic energy to form li