The present invention relates to organic light emitting elements, comprising thermally activated delayed fluorescence (TADF) emitters and/or hosts of formula ##STR00001##
which have a sufficiently small energy gap between S.sub.1 and T.sub.1 (E.sub.ST) to enable up-conversion of the triplet exciton from T.sub.1 to S.sub.1. The organic light emitting elements show high electroluminescent efficiency.