Organic electroluminescence from singlet and triplet exciplexes: Exciplex electrophosphorescent diode

We have observed emission from singlet and triplet exciplexes in electron donor (D)–acceptor (A) organic electroluminescent systems. The exciplex singlet-to-triplet fraction appears to be a function of electronic properties of the (D–A) complex molecular components and applied electric field. The fluorescence from exciplex singlets could be eliminated using a heavy atom (Gd)-substituted acceptor molecule allowing the efficient intersystem crossing of singlet into triplet exciplex states. By this a pure exciplex electrophosphorescent diode has been realized. These findings are of importance for the understanding of the exciplex formation mechanism and, thus, for material choice in device applications.