least one of R1 and R2 or R3 and R4 is an aryl group 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 light an