Organic electroluminescent materials and devices

A composition comprising:

• a compound S1;
• and
• a compound A1;
• wherein when the composition is formed into an emissive layer of an organic electroluminescent device, the compound S1 functions as an organometallic sensitizer that transfers energy to the compound A1 and the compound A1 is an acceptor that is an emitter;
• wherein the compound A1 has a vertical dipole ratio (VDR) value ≥0.33.

An organic light emitting device (OLED) comprising:

• a substrate;
• a first electrode;
• an organic emissive region disposed over the first electrode;
• an enhancement layer disposed over the organic emissive region opposite from the first electrode;
• wherein the emissive region comprises:
• a compound S1;
• and
• a compound A1;
• wherein the compound S1 is a sensitizer that transfers energy to the compound A1, and the compound A1 is an acceptor that is an emitter;
• wherein the enhancement layer comprises a plasmonic material exhibiting surface plasmon resonance that non-radiatively couples to the compound A1, compound S1, or both compounds A1 and S1, and transfers excited state energy from the compound A1, compound S1, or from both compounds A1 and S1, to non-radiative mode energy of surface plasmon polaritons.