Novel compounds of formula I are described ##STR00001## wherein E corresponds to the formula ##STR00002## or to the formula ##STR00003## and the radicals R.sub.1, R.sub.2, R.sub.11, R.sub.22, R'.sub.22, R'.sub.33 and R'.sub.33 are as defined in claim 1. Compounds of formula I are suitable for stabilizing organic material, especially plastics materials, surface-coatings, cosmetic preparations, sun protection agents or photographic material, against damage by light, oxygen and/or heat.