Use of transition metal-carbene complexes which do not comprise any cyclometallation via non-carbenes in OLEDs

An organic light-emitting diode comprising at least one transition metal-carbene complex of formula (I)

• in which the symbols are each defined as follows:
• M1 is a metal atom selected from the group consisting of transition metals of group IIB, IIIB, IVB, VB, VIB, VIIB, VIII of the Periodic Table of the Elements (CAS version) and Cu, in any oxidation state possible for the particular metal atom;
• L is a mono- or dianionic ligand which may be mono- or bidentate selected from the group consisting of Cl−, Br−, I−, CN−, OAc−, alkyl radical which are bonded to the transition metal atoms M1 via a sigma bond and acetylacetoneate and derivatives thereof;
• m is from 0 to 5;
• o is 0;
• n is from 1 to 6;
• p is the charge of the complex:
• 0, 1, 2, 3, 4;
• W− is a monoanionic counterion;
• where m, n and p are dependent upon the oxidation state and coordination number of the metal atom used and upon the charge of the ligands and the overall charge of the complex, and
• carbene is a carbene ligand selected from the group consisting of
• in which the symbols are each defined as follows:
• R1, R2
• are each independently hydrogen, alkyl or cycloalkyl groups, where the groups may be substituted by CH3, F, Cl or CN or unsubstituted, or a C6-aryl radical, which is substituted by at least two of the substituents mentioned, where the substituents are arranged in the ortho position to the further bonding site of the aryl radical, in the case of three substituents, they are arranged in the ortho position (two of the three substituents) and p-position (third substituent) to the further bonding site of the aryl radical;
• X1, X2, X3, X4
• are each independently alkylene, 1,2-phenylene,
• alkynylene or alkenylene groups, where the groups may be substituted or unsubstituted;
• A, A′, A″, A′″
• are each R18, and
• B, B′, B″, B′″
• are each R19, where
• R18 in A, A′, A″, A′″ and R19 in B, B′, B″, B′″ may in each case be defined identically or differently;
• or
• groups A and B, A′ and B′, A″ and B″ or A′″ and B′″
• each independently form a radical of the following formula:
• so as to give rise to a fused ring, where
• Z′ in the A and B, A′ and B′, A″ and B″ and A′″ and B′″ groups may in each case be defined identically or differently;
• R18, R19
• are each hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl, aralkyl, heteroaryl, alkynyl or alkenyl groups, where the groups may be substituted or unsubstituted, or a substituent with donor or acceptor action;
• Z′ are each independently CR21 or N;
• R21 is hydrogen, alkyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, aralkyl, alkynyl alkenyl groups, where the groups may be substituted or unsubstituted, or a radical with donor or acceptor action, or in each case two R21 radicals together form a fused ring which may optionally comprise at least one heteroatom
• wherein the carbene ligand(s) in the transition metal complexes of the formula I is bonded to the transition metal exclusively via carbene carbon atoms.