Highly luminescent phthalimide- and maleimide-based molecules having donor acceptor donor electronic configurations have been developed. A phthalimide-based material exhibited highly efficient green delayed fluorescence owing to its small singlet triplet energy gap. An organic light-emitting diode using the molecules as an emitter exhibited a high maximum external electroluminescence quantum efficiency of 11.5%, which exceeds those obtained with common fluorescent emitters.