NOVELTY - Fused heterocyclic compounds (I), are new.    USE - (I) or the oligomers, polymers or dendrimers are useful: in an electronic 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 optical detectors, organic photoreceptors, organic field-quench devices, light-emitting electrochemical cells, organic laser diodes and organic plasmon emitting devices; and as an electron transport material, host materials, electron blocking material or as emitting material (all claimed).    ADVANTAGE - (I): provide organic light emitting diodes with a long operational life, good efficiency and low operating voltage; and exhibit improved thermal stability.    DETAILED DESCRIPTION - Fused heterocyclic compounds of formula (I), are new.    Ar1=5-60 membered (hetero)aromatic ring system (optionally substituted with one or more R);    X=B(R), C(R) 2, -CR=CR-, -CR=N-, Si(R) 2, O, S, SO 2, N(R) or P(=O)R;    Z=C (when X is bonded to Z) or N or CR1 (when no X is bonded to Z);    W1=CR1 or N, where at least one Z or W is CR1;    Y1=C (when X is bonded to Y1) or N or CR2 (when no X is bonded to Y1); either    R, R1, R2=H, D, F, Cl, Br, I, CHO, N(R3) 2, C(=O)R3, P(=O)(R3) 2, S(=O)R3, S(=O) 2R3, CR3=C(R3) 2, CN, NO 2, Si(R3) 3, B(OR3) 2, OSO 2R3, OH, 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 R3, and where one or more non-adjacent CH 2-groups are optionally replaced by R3C=CR3, C?=C, Si(R3) 2, Ge(R3) 2, Sn(R3) 2, C=O, C=S, C=Se, C=NR3, P(=O)(R3), SO, SO 2, NR3, O, S or CONR3, and one or more H-atoms are replaced by D, F, Cl, Br, I, CN or NO 2), or 5-60 membered mono- or polycyclic (hetero)aromatic ring system or 5-60 membered (hetero)aryloxy (both optionally substituted by one or more non-aromatic residue of R3); or    two or more R, R1, R2 bonded together=mono or polycyclic, aliphatic or aromatic ring system; either    R3=H, D, F or 1-20C-aliphatic or (hetero)aromatic organic residue, in which one or more H-atoms are optionally replaced by F; or    two or more R3 bonded together=mono- or polycyclic, aliphatic or aromatic ring system;    m, n=0 or 1, where m + n is greater than or equal to 1;    s=1-3, preferably 1; and    v=0 or 1 (preferred).    Provided that at least one R1 group must present that is 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 R3, and where one or more non-adjacent CH 2-groups are optionally replaced by R3C=CR3, C=C, Si(R3) 2, Ge(R3) 2, Sn(R3) 2, C=O, C=S, C=Se, C=NR3, P(=O)(R3), SO, SO 2, NR3, O, S or CONR3, and one or more H-atoms are replaced by D, F, Cl, Br, I, CN or NO 2), or 5-60 membered mono- or polycyclic (hetero)aromatic ring system (optionally substituted by one or more non-aromatic residue of R3).    INDEPENDENT CLAIMS are also included for the following:    (1) preparation of (I); and    (2) oligomers, polymers or dendrimers containing one or more (I).