NOVELTY - Substituted aza-dibenzothiophene compounds or substituted azadibenzofuran compounds (I) are new.    USE - (I) are useful in first device comprising organic light emitting device (claimed). (I) are useful in: flat panel displays, illumination, backlighting and consumer products comprising flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants, laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen or a sign; and in optoelectronic devices e.g. organic solar cells and organic photodetectors.    ADVANTAGE - (I) (preferably the substituted aza-dibenzothiophene compounds) are produced at higher yields, preferably not greater than 50%. (I): has improved stability and improved efficiency; provides long lifetime, low operational voltage and high efficiency without energy quenching.    DETAILED DESCRIPTION - Substituted aza-dibenzothiophene compounds or substituted azadibenzofuran compounds of formula (I) are new.    X1-X8 = C or N;    Y1 = S or O;    R1, R2 = mono to tetra substitutions comprising H, alkyl, (hetero)aryl, halo or 15 fused aryl moieties e.g. substituted triphenylene moieties of formulae (II)-(IX), substituted 9H-carbazole-9-yl moieties of formula (X), substituted diphenylamine-1-yl moieties of formula (XI);    R1a, R2a, R3a, R4a = mono to penta substitutions comprising H, (hetero)alkyl or (hetero)aryl; and    m, n = 0-4, where m+n is 2-6.    Provided that at least one of X1-X8 is N. INDEPENDENT CLAIMS are also included for:    (1) the preparation of (I); and    (2) a first device comprising an organic light emitting device (100), an anode (115), a cathode (160), and an organic layer disposed between the anode and the cathode, where the organic layer comprises (I).    DESCRIPTION OF DRAWING(S) - The figure shows an organic light emitting device.    Organic light emitting device (100)    Substrate (110)    Anode (115)    Emissive layer (135)    Cathode (160)