NOVELTY - Metal complexes (I) are new.    USE - (I) are useful in: a device where the device is an organic LED (OLED) such as a phosphorescent OLED device or a fluorescent OLED device, or a full color display; a photovoltaic device; a luminescent display device; and a light emitting device (all claimed).    ADVANTAGE - (I) exhibit improved performance in optical and electro-optical devices, and provide improved efficiency and/or operational lifetimes in lighting devices, when compared to conventional materials.    DETAILED DESCRIPTION - Metal complexes of formula (I) are new.    L1a-L4a=optionally substituted aryl, cycloalkyl, cycloalkenyl, heterocyclyl, heteroaryl, carbene or N-heterocyclic carbene;    Z1a-Z3a=present or absent, and if present each of Z1a, Z2a and Z3a is A1a, A2a, or A3a;    A1a, A2a, A3a=O, S, S=O, SO 2, Se, NR3a, PR3a, R1bP=O, CR1cR2c, C=O, SiR1cR2c, GeR1cR2c, BH, P(O)H, PH, NH, CR1cH, CH 2, SiH 2, SiHR1c, BH or BR3a;    M1a=Pt, Pd, Au, Ir, Rh, Ru, Fe, Co, Ni, Cu, Zn, Ag, Hg, Cd or Zr;    at least one of L1a-La=substituted tricyclyl moiety of formula (a1) or (a2);    m, n=0-4;    V1a, X1a and Y1a=V1b, V2b, V3b, V4b, O, S, S=O, SO 2, Se, NR3a, PR3a, R1cP=O, CR1cR2c, C=O, SiR1cR2c, GeR1cR2c, BH, P(O)H, PH, NH, CR1cH, CH 2, SiH 2, SiHR1c, BH or BR3a, or any one of e.g. -CH 2=CH 2-, -CH=C(R1b)-, -C(R1c)=C(R2c)-, 1,2-phenylene, substituted 1,2-phenylene moiety of formula (k1), N-containing heteroaryl moiety of formulae (k2)-(k11), -N=C(R1b)-, -N=CH-, -N=N-, -CH 2CH2-, -CR1cR2cCR3aR4a-, -CR1cR2c(CR3aR4a)n-, -N(R1c)CR2cR3a-, -OCR1cR2c-, -O(CR1cR2c) n-, -(OCR1cR2c) n-, -SCR1cR2c-, -S(CR1cR2c) n-, -(SCR1cR2c) n-, -B(R1c)CR2cR3a-, -B(R1c)(CR2cR3a)n-, -(B(R1c)CR2cR3a) n-, -Si(R1c)(R2c)-C(R3a)(R4a)-, -Si(R1c)(R2c)-(C(R3a)(R4a)) n-, -(Si(R1c)(R2c)-C(R3a)(R4a)) n-, -P(R1c)(=O)-(C(R2c)(R3c)) n, -(P(R1c)(=O)-C(R2c)(R3c)) n, -CH=CH(CH 2) n-, -C(R1c)=C(R2c)(CR3aR4a) n-, -N=CH-(CH2) n-, -N=C(R1c)(CR2cR3a)n-, -CH=N-(CH 2)n-, -C(R1c)=N-(CR2cR3a) n-, -CH=CH-(N(R1c)) n-, -C(R1c)=C(R2c)-(N(R3a)) n-, -CH=CH-(CH=CH)n-, -C(R1c)=C(R2c)(C(R3a)=C(R4a)) n-, -N(R1b)C(O)-, -OC(O)-, -S(O)CR1cR2c-, -S(O)(CR1cR2c) n-, -(S(O)CR1cR2c) n-, -SO2CR1cR2c-, SO2(C(R1c)(R2c)) n- or -(SO2CR1cR2c)n-, where at least one of V1a, X1a and Y1a is V1b, V2b, V3b or V4b;    V1b-V4b=N, C, CH, P, B, SiH or Si, where V1b-V4b are coordinated to M1a, and each of V1b-V4b are optionally substituted; and    R1b, R1c, R2c, R3a and R4a=H, aryl, cycloalkyl, cycloalkenyl, heterocyclyl, heteroaryl, alkyl, alkenyl, alkynyl, deuterium, halo, OH, thiol, nitro, cyano, amino, mono- or di-alkylamino, mono- or diaryl amino, alkoxy, aryloxy, haloalkyl, aralkyl, ester, nitrile, isonitrile, alkoxycarbonyl, acylamino, alkoxycarbonylamino, aryloxy-carbonylamino, sulfonylamino, sulfamoyl, carbamoyl, alkylthio, sulfinyl, ureido, phosphoramide, mercapto, sulfo, carboxy, hydrazino, substituted silyl, polymerizable, and/or their conjugates.