Transition metal complexes with carbene ligands as emitters for organic light-emitting diodes (OLEDs)

1. An organic light-emitting diode comprising at least one uncharged transition metal complex of the formula (I) comprising at least one carbene ligand

wherein the symbols have the following meanings:

M 1 is Ir in any oxidation state possible for the respective metal atom;

carbene is a carbene ligand which may be uncharged or monoanionic and monodentate, bidentate or tridentate, with the carbene ligand also being able to be a biscarbene or triscarbene ligand;

L is a monoanionic or dianionic ligand, which may be monodentate or bidentate;

n is the number of carbene ligands, wherein n is at least 1 and when n>1 the carbene ligands in the complex of the formula I can be identical or different;

m is the number of ligands L, wherein m can be 0 or ≧1 and when m>1 the ligands L can be identical or different;

o is the number of ligands K, wherein o is 0;

wherein the sum n+m+o is dependent on the oxidation state and coordination number of the metal atom and on the denticity of the ligands carbene, L and also on the charge on the ligands carbene and L, with the proviso that n is at least 1,

wherein the carbene ligand or ligands has/have the formula II

wherein the symbols have the following meanings:

Do 1 is S or 0;

r is 0;

p is 0;

q is 0;

Y 1 and Y 2 together form a bridge between the donor atom Do 1 and the nitrogen atom N which has two atoms of which one is a carbon atom, and the other is a carbon or nitrogen atom;

R 1 and R 2 together form a bridge having a total of from three to five atoms of which one or two atoms may be heteroatoms and the remaining atoms are carbon atoms, so that the group

forms a five- to seven-membered, ring which may contain, in addition to the existing double bond, one further double bond or in the case of a six- or seven-membered ring two further double bonds and may be substituted by alkyl or aryl groups and may contain at least one heteroatom.

2. The organic light-emitting diode as claimed in claim 1 , wherein the uncharged transition metal complexes are employed as emitter molecules.

3. The organic light-emitting diode as claimed in claim 1 , wherein the carbene ligand or ligands is/are bidentate.

4. The organic light-emitting diode as claimed in claim 1 , wherein the carbene ligand or ligands is/are monoanionic.

5. The organic light-emitting diode as claimed in claim 1 , wherein the group

denotes the structure

wherein the symbols have the following meanings:

Z is CH or N and can be located in the o, m or p position relative to the point of linkage of the group to the carbene ligand;

R 12 is an alkyl, aryl, heteroaryl or alkenyl radical, or 2 radicals R 12 together form a fused-on ring which may contain one or more heteroatoms, or R 12 is a radical which acts as a donor or acceptor; and

t is 0 to 3 and when t>1 the radicals R 12 can be identical or different.

6. A light-emitting layer comprising at least one transition metal complex as claimed in claim 1 .

7. An OLED comprising a light-emitting layer as claimed in claim 6 .

8. A device selected from the group consisting of stationary VDUs and mobile VDUs each comprising an OLED as claimed in claim 1 .

9. A device selected from the group consisting of stationary VDUs and mobile VDUs each comprising an OLED as claimed in claim 7 .

10. The organic light-emitting diode as claimed in claim 1 , wherein the two atoms of the bridge formed by Y 1 and Y 2 are substituted, and the substituents of the groups Y 1 and Y 2 together form a bridge having a total of four atoms of which one or two may be N-heteroatoms and the remaining atoms are carbon atoms, so that the Y 1 and Y 2 together with the bridge form a six-membered aromatic ring.