Cyclometallated iridium carbene complexes for use as hosts

A light emitting device, comprising:

• (a) an anode;
• (b) a cathode;
• (c) an organic layer disposed between the anode and the cathode, wherein the organic layer comprises a host and a dopant, and the host comprises a compound having at least one carbene atom coordinated to iridium, and the compound has the structure:
• wherein the dotted lines represent optional double bonds;
• ring A is independently an aromatic cyclic, heterocyclic, fused cyclic, or fused heterocyclic ring with at least one carbon atom coordinated to Ir, wherein ring A can be optionally substituted with one or more substituents Ra;
• R1 is independently selected from hydrogen, alkyl, alkenyl, alkynyl, aralkyl, aryl, heteroaryl, substituted aryl, substituted heteroaryl, or a heterocyclic group;
• R2–R5, and Ra are independently selected from hydrogen, alkyl, alkenyl, alkynyl, aralkyl, CN, CF3, CO2R′, C(O)R′, C(O)NR′2, NR′2, NO2, OR′, SR′, SO2, SOR′, SO3R′, halo, aryl, heteroaryl, substituted aryl, substituted heteroaryl, or a heterocyclic group;
• and additionally or alternatively, two R or Ra groups on the same or adjacent ring, together form independently a 5 or 6-member cyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl;
• and wherein said cyclic group is optionally substituted by one or more substituents J;
• each substituent J is independently selected from the group consisting of R′, CN, CF3, C(O)OR′, C(O)R′, C(O)NR′2, NR′2, NO2, OR′, SR′, SO2, SOR′, or SO3R′, and additionally, or alternatively, two J groups on adjacent ring atoms form a fused 5- or 6-membered aromatic group;
• each R′ is independently selected from halo, H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl;
• b is 0, 1, 2, or 3.