Metal complexes comprising at least one polycyclic aromatic ligand and bearing at least one deuterium atom, an organic light-emitting diode comprising at least one inventive metal complex, a light-emitting layer comprising at least one inventive metal complex, an organic light-emitting diode comprising at least one inventive light-emitting layer, the use of the at least one inventive metal complex in organic light-emitting diodes, and a device selected from the group consisting of stationary visual display units such as visual display units of computers, televisions, visual display units in printers, kitchen appliances and advertising panels, illuminations, information panels and mobile visual display units such as visual display units in cellphones, laptops, digital cameras, vehicles, and destination displays on buses and trains, comprising at least one inventive organic light-emitting diode.