NOVELTY - Phosphorescent tetradentate metal complexes (Q) are new.    USE - (Q) are useful: as full color display, an organic LED (OLED) and phosphorescent OLED in a photovoltaic device and luminescent display device for a light emitting device (all claimed) such as organic light emitting device and in optical and electro-optical devices including photo-absorbing devices such as solar- and photo-sensitive devices, photovoltaic devices, photo-emitting devices, or devices capable of both photo-absorption and emission; and as luminescent labels in bio-applications and/or anti-cancer agents.    ADVANTAGE - (Q) provide improved efficiency, processing ability, efficient emission or absorption, high stability, and/or operational lifetimes to the light emitting device.    DETAILED DESCRIPTION - Phosphorescent tetradentate metal complexes (Q) of formulae (I)-(III) are new.    L1-L3 = optionally substituted aryl, heterocyclyl, carbene or N-heterocyclic carbene;    L4 = optionally substituted aryl, heterocyclyl, carbene, N-heterocyclic carbene, Cl, F, nitrile, substituted alkyl, substituted alkenyl, or 3-6C-alkynyl, where L1 and L2 are an emitting portion of (Q), L3 and L4 are an ancillary portion of (Q), L1 and L2 are linked directly, L2 and L3 are linked directly or through a linking atom (A1), and L3 and L4 are unlinked, linked directly, or, when L4 represents optionally substituted aryl, heterocyclyl, carbene, or N-heterocyclic carbene, linked through a linking atom A2;    A1, A2 = O, S, N, C, P, Si or B;    V1-V4 = N, C, P, B, Si, or coordinated atoms of L1, L2, L3 or L4, respectively;    M = Pt, Au, Ir, Rh, Ru, Fe, Co, Ni, Cu, Zn, Ag, Hg, Cd or Zr; and    Ra1-Rd1 = mono-, di-, tri, or tetra-substitution consisting of (halo)alkyl, aralkyl, alkenyl, alkynyl, aryl, amino, mono- or dialkylamino, mono- or diarylamino, alkoxy, aryloxy, heteroaryl (all optionally substituted), D, halo, OH, thiol, nitro, CN, alkoxycarbonyl, acyloxy, acylamino, alkoxycarbonylamino, aryloxycarbonylamino, sulfonylamino, sulfamoyl, carbamoyl, alkylthio, sulfinyl, ureido, phosphoramide, mercapto, sulfo, carboxyl, hydrazino, substituted silyl, or polymeric group.