NOVELTY - (Hetero)aryl compounds (I) are new.    USE - (I) or the mixture is useful in an electronic device, preferably an organic electroluminescent device, where the electronic devices are organic electroluminescent devices, organic integrated circuits, organic field-effect transistors, organic thin film transistors, organic light emitting transistors, organic solar cells, organic photoreceptors, organic field-quenching devices, light-emitting electrochemical cells and organic laser diodes. (I) are useful as host material together with the emitter compound(s) (all claimed).    ADVANTAGE - (I) provide organic electroluminescent device with improved durability, efficiency and operating voltage, and improved color fastness to the device, preferably in blue-emitting devices. (I) exhibit: improved thermal stability, improved vapor deposition behavior and reduced crystallinity for vacuum-based production processes; and improved solubility and improved film formation for solution-based production processes.    DETAILED DESCRIPTION - (Hetero)aryl compounds of formula (Z-(Y1) n) (I) are new.    Z=(hetero)aromatic ring system containing at least 15 and at most 60 ring atoms (optionally substituted with one or more R), where Z comprises many (hetero)aryl groups containing at least 15 ring atoms and these (hetero)aryl groups are bonded over a non-aromatic optionally conjugated unit comprising sp 2- or sp-hybridized C-atoms or sp 2-hybridized N-atoms or over single bond, and these aryl groups have a structure of formula (II);    X=CR or N, where not more than 2 adjacent X correspond to the same N;    Y1=phenyl-, biphenyl-, terphenyl-, diphenyltriazinyl-, naphthyl-, methyl-, pyridinyl-, pyrimidinyl-, pyrazinyl-, triazinyl-, thiophenyl-, furanyl-, quinolinyl-, isoquinolinyl-, imidazolyl-, benzimidazolyl- or quinazolinyl (all contains two or more deuterium atoms and all optionally substituted with one or more R1), where two or more Y1 are optionally bonded by single bond or by one or more R1; either    R, R1=H, D, F, Cl, Br, I, CN, Si(R2) 3, NO 2, (hetero)aromatic ring system having 5-60 ring atoms (optionally substituted one or more R2) or linear 1-40C-alkyl or -(thio)alkoxy or 2-40C-alkenyl- or -alkynyl or branched or cyclic 3-40C-alkyl or -(thio)alkoxy (all optionally substituted with one or more R2), where one or more adjacent or non-adjacent CH 2-groups are optionally replaced by -C?=C-, -R2C=CR2-, Si(R2) 2, C=O, C=S, C=Se, C=NR2, P(=O)(R2), SO, SO 2, NR2, O, S, COO or CONR2; or    two or more R and/or R1 bonded together=mono- or polycyclic aliphatic or (hetero)aromatic ring system; either    R2=H, D or 1-20C-aliphatic or (hetero)aromatic organic residue, in which one or more H atoms are optionally replaced by D or F; or    two or more adjacent or non-adjacent R2 bonded together=mono- or polycyclic aliphatic or (hetero)aromatic ring system; and    n=1-15.    INDEPENDENT CLAIMS are included for:    (1) the preparation of (I);    (2) a mixture comprising (I) and one or more emitter compounds; and    (3) a formulation comprising (I) or the mixture and at least one solvent.