NOVELTY - Electronic device comprises at least one fused (hetero)aryl compound (I).    USE - (I) is useful as matrix material for fluorescent or phosphorescent emitters, preferably for phosphorescent emitter, and/or in a hole blocking layer, an electron transport layer, an electron-blocking layer or exciton blocking layer, a hole transport layer and/or an optical coupling layer (claimed).    ADVANTAGE - The electronic device has high efficiencies and steep current-voltage characteristics with low threshold voltages, and has improved durability and improved operating voltage. (I) has improved stability.    DETAILED DESCRIPTION - Electronic device comprises at least one fused (hetero)aryl compound of formula (I).    X=C=O, C(R) 2, NR, O, S, C=S, C=NR, C=C(R) 2, Si(R) 2, BR, PR, P(=O)R, SO or SO 2;    Y1=C (when Ar1 is 6-ring-aryl- or heteroaryl group), or C or N (when Ar1 is 5-ring-heteroaryl group);    E1= bond, C(R)2, NR, O, S, C=O, C=S, C=NR, C=C(R) 2, Si(R) 2, BR, PR, P(O)R, SO or SO2;    Ar1-Ar3=5-30 membered (hetero)aromatic ring system (optionally substituted by one or more R);    R=H, D, F, Cl, Br, I, CN, NO 2, N(Ar4) 2, N(R1) 2, C(=O)Ar4, C(=O)R1, P(=O)(Ar4) 2, or linear 1-40C-(thio)alkyl or -alkoxy, branched or cyclic 3-40C-(thio)alkyl or -alkoxy, 2-40C-alkenyl or -alkynyl (all optionally substituted by one or more R1, and where one or more non-adjacent CH 2-groups are optionally replaced by R1C=CR1, CC, Si(R1) 2, Ge(R1) 2, Sn(R1) 2, C=O, C=S, C=Se, C=NR1, P(=O)(R1), SO, SO 2, NR1, O, S or CONR1, and one or more H-atoms are optionally replaced by D, F, Cl, Br, I, CN or NO 2), or 5-80 (preferably 5-60) membered (hetero)aromatic ring system or 5-60 membered (hetero)aryloxy (optionally substituted by one or more R1) and/or 5-60 membered (hetero)aryloxy (optionally substituted with one or more R1); or    two or more R together=mono or polycyclic, aliphatic or (hetero)aromatic ring system (optionally substituted by one or more R1);    R1=H, D, F, Cl, Br, I, CN, NO 2, N(Ar4) 2, N(R2)2, C(O)Ar4, C(O)R2, P(O)(Ar4) 2, or linear 1-40C-(thio)alkyl or -alkoxy, branched or cyclic 3-40C-(thio)alkyl or -alkoxy, 2-40C-alkenyl or -alkynyl (all optionally substituted by one or more R2, and where one or more non-adjacent CH 2-groups are optionally replaced by R2C=CR2, CC, Si(R2) 2, Ge(R2) 2, Sn(R2) 2, C=O, C=S, C=Se, C=NR2, P(=O)(R2), SO, SO 2, NR2, O, S or CONR2, and one or more H-atoms are optionally replaced by D, F, Cl, Br, I, CN or NO 2), or 5-60 membered (hetero)aromatic ring system or 5-60 membered (hetero)aryloxy (optionally substituted by one or more R2) and/or 5-60 membered (hetero)aryloxy (optionally substituted with one or more R2); or    two or more R1 together=mono or polycyclic, aliphatic or (hetero)aromatic ring system (optionally substituted by one or more R2);    Ar4=5-30 membered (hetero)aromatic ring system (optionally substituted with one or more non-aromatic residues of R2), where two residues of Ar4 are optionally joined to one another at the same N- or P-atom by a single bond or a bridge comprising N(R2), C(R2) 2or O;    R2=H, D, F, CN, 1-20C-aliphatic hydrocarbyl or 5-30 membered (hetero)aromatic ring system (optionally one or more H atoms are optionally replaced by D, F, Cl, Br, I or CN); or    two or more R2 together=a mono- or polycyclic, aliphatic or (hetero)aromatic ring system.    INDEPENDENT CLAIMS are included for:    (1) (I), which excludes 2-bromo-3-phenyl-7b-aza-benzo(e)acephenanthrylen-8-one, 3-phenyl-7b-aza-benzo(e)acephenanthrylen-8-one, 1-phenyl-7b-aza-benzo(e)acephenanthrylen-8-one, dibenzo(b,h)quinolino(3,2,1-de)(1,5)naphthyridine-6,16-dione or fused (hetero)aryl compounds of formula (a1)-(a8);    (2) the preparation of (I); and    (3) oligomers, polymers or dendrimers containing one or more (I).