The invention relates to the use of transition metal complexes of formula (I) in organic light-emitting diodes, wherein: M1 represents a metal atom; carbene represents a carbene ligand; L represents a monoanionic or dianionic ligand; K represents a neutral monodentate or bidentate ligand selected from the group consisting of phosphines, CO, pyridines, nitriles and of conjugated dienes that form a π-complex with M1; n represents a number of carbene ligands, whereby n is at least 1; m represents a number of ligands L, whereby m can be 0 or = 1; o represents a number of ligands K, whereby o can be 0 or = 1, and the sum n + m + o depends on the oxidation stage and coordination number of the metal atom used and on the dentation of the ligands carbene, L and K as well as on the charge of the ligands carbene and L, with the condition that n is at least 1. The invention also relates to an OLED containing these transition metal complexes, a light-emitting layer containing these transition metal complexes, OLED's containing this light-emitting layer, devices that contain an inventive OLED, and to special transition metal complexes containing at least two carbene ligands.