NOVELTY - Organic electroluminescent compound, is new.    USE - The organic electroluminescent compound is useful for preparing formulation and first device, e.g. a consumer product, a light panel (all claimed), organic light-emitting device, optoelectronic devices such as organic solar cells and organic photodetectors, and organic transistors. Consumer product includes flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, three dimensional (3-D) displays, vehicles, a large area wall, theater or stadium screen, or a sign.    ADVANTAGE - The organic electroluminescent compounds provide: (1) a broad potential for ligand modification and, have tunable photophysical properties, i.e. emission energies can be tuned throughout visible spectrum; (2) the new geometry does not undergo a flattening distortion in the excited state, which can potentially give these complexes higher photoluminescent quantum yield (PLQY) values in the solid state as well as in solution; (3) fast radiative rates; (4) the monodentate carbene may be a chromophore or an ancillary ligand by rational modification, and similarly for the other ligands; and (5) enhanced rigidity and steric-bulk of the complexes results in their increased stability in air as solids or in solution. The opto-electronic devices that make use of organic electroluminescent compound are relatively inexpensive, thus organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. For organic light emitting devices, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.    DETAILED DESCRIPTION - Organic electroluminescent compound of formula (I) or (II), is new.    Y'=a carbene moeity coordinated to a trivalent copper atom Cu;    L1-L3=three monodentate ligands (in Formula I); or a single tridentate ligand (in Formula II) chelated by X; and    X=B-H, C-H, N, P, or P=O.    An INDEPENDENT CLAIM is included for a first device comprising a first organic light emitting device, the first organic light emitting device comprising: an anode; a cathode; and an organic layer, disposed between the anode and the cathode, comprising the organic electroluminescent compound.