NOVELTY - Fused (hetero)aryl compounds (A) are new.    USE - (A) or the oligomers, polymers or dendrimers are useful in an electronic device, preferably an organic electroluminescent device, where the electronic devices are integrated organic electroluminescent devices, organic integrated circuits, organic field-effect transistors, organic thin film transistors, organic light emitting transistors, organic solar cells, organic optical detectors, organic photoreceptors, organic field-quench devices, light-emitting electrochemical cells, organic laser diodes and organic plasmon emitting devices. (A) are useful: as matrix material for fluorescent or phosphorescent emitter, preferably for phosphorescent emitters; and in a hole blocking layer, an electron transport layer, an electron-blocking and exciton blocking layer and/or in a hole-transport layer (all claimed).    ADVANTAGE - (A) provide organic electroluminescent device with improved durability, efficiency and operating voltage.    DETAILED DESCRIPTION - Fused (hetero)aryl compounds (A) of formulae (I) and (II) are new.    X = N, P or P=O;    Y1 = C(R)2, NR, O, S, C=O, C=S, C=NR, C=C(R)2, Si(R)2, BR, PR, AsR, SbR, BiR, P(=O)R, As(=O)R, Bi(=O)R, SO, SeO, TeO, SO2, SeO2, TeO2 or a chemical bond, with the proviso that not all three Y1 groups are single bond; either    R = N(Ar1)2, N(R1)2, C(=O)Ar1, C(=O)R1, P(=O)(Ar1)2, linear 1-40C-alkyl, -alkoxy or -thioalkyl, branched or cyclic 3-40C-alkyl, -alkoxy or -thioalkyl, 2-40C-alkenyl or 2-40C-alkynyl, 5-80 membered (hetero)aromatic ring or 5-60C-(hetero)aryloxy (all optionally substituted by one or more R1), H, D, F, Cl, Br, I, CN or NO2, where one or more non-adjacent CH2-groups are optionally replaced by R1C=CR1, C?=C, Si(R1)2, Ge(R1)2, Sn(R1)2, C=O, C=S, C=Se, C=NR1, P(=O)(R1), SO, SO2, NR1, O, S or CONR1 and one or more H-atoms are optionally replaced by D, F, Cl, Br, I, CN or NO2; or    two or more R = monocyclic or polycyclic, aliphatic, (hetero)aromatic ring (optionally substituted with one or more R1); either    R1 = N(Ar1)2, N(R2)2, C(=O)Ar1, O(O)R2, P(=O)(Ar1)2, linear 1-40C-alkyl, -alkoxy or -thioalkyl or branched or cyclic 3-40C-alkyl, -alkoxy or thioalkyl or 2-40C-alkenyl or alkynyl, 5-60 membered (hetero)aromatic ring or 5-60C-(hetero)aryloxy (all optionally substituted by one or more R2), H, D, F, Cl, Br, I, CN or NO2, where one or more non-adjacent CH2-groups are optionally replaced by R2C=CR2, C?=C, Si(R2)2, Ge(R2)2, Sn(R2)2, C=O, C=S, C=Se, C=NR2, P(=O)(R2), SO, SO2, NR2, O, S or CONR2, and one or more H-atoms are optionally replaced by D, F, Cl, Br, I, CN or NO2; or    two or more R1 together = monocyclic or polycyclic, aliphatic, (hetero)aromatic ring (optionally substituted with one or more R2); either    R2 = H, D, F, CN, 1-20C-aliphatic hydrocarbon, 5-30C-(hetero)aromatic ring system, in which one or more H atoms are optionally replaced by D, F, Cl, Br, I or CN; or    two or more adjacent R2 together = mono- or polycyclic, aliphatic, (hetero)aromatic ring system;    Ar1 = 5-30 membered (hetero)aromatic ring system (optionally substituted by one or more non-aromatic residue of R2), where two Ar1, which bind to the same nitrogen atom or phosphorus atom, are bridged to one another by a single bond or a bridge comprising N(R2), C(R2)2 or O;    L = bivalent or higher valent linear 1-40C-alkylene-, -alkylidene, -alkyleneoxy- or -thioalkyleneoxy, branched or cyclic 3-40C-alkylene, -alkylidene, -alkyleneoxy or -thioalkyleneoxy or 2-40C-alkenylene or -alkynylene, or 5-80 membered bivalent (hetero)aromatic ring system or P(R1)3-p, P(=O)(R1)3-p, C(R1)4-p, Si(R1)4-p, N(Ar1)3-p or their combination of two to five of these systems (all optionally substituted with one or more R1) , or a chemical bond, where one or more non-adjacent CH2-groups are optionally replaced by -R1C=CR1-, -C?=C-, Si(R1)2, Ge(R1)2, Sn(R1)2, C=O, C=S, C=Se, C=NR1, P(=O)R1, S=O, SO2, -O-, -S- or -CONR1-, and one or more H-atoms are optionally replaced by D, F, Cl, Br, I, CN or NO2;    n = 0-2, where n is 0 then Y1 is H or R1, with the proviso that, per unit, at least two n is not equal to zero;    p = 2-6, with the proviso that p is not greater than the maximum valence of L, where at least one R is a (hetero)aryl group of formula (a3), (R1-C(=O)-(Ar1)m-) (a4), (a5) or (a6), at least one Y1 is N-R, and R is hetero(aryl) groups of formulae (a7)-(a9), and/or at least one L is a (hetero)aryl group of formulae (a10)-(a15); and    m = 0 or 1.    INDEPENDENT CLAIMS are included for:    (1) the preparation of (A); and    (2) oligomers, polymers or dendrimers containing one or more (A), where one or more bonds of (A) remain(s) to the polymer, oligomer or dendrimer.