TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation: (Disclosed) A silyl-substituted azadibenzofuran or azadibenzothiophene compound is prepared by dissolving suitable intermediates, e.g. 8-bromobenzofuro(3,2-b)pyridine and triphenyl-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)silane in toluene, adding ethanol, degassing reaction mixture, dissolving potassium carbonate in water, degassing solution, adding into reaction mixture, adding tetrakis(triphenylphosphine)palladium(0), heating while stirring, cooling to room temperature, pouring into water and ethyl acetate, separating layers, extracting aqueous layer with ethyl acetate, washing combined organic layers with water, drying over sodium sulfate, removing solvent in vacuo, dissolving crude product in chloroform, adding 3% aqueous sodium cyanide solution, heating mixture under reflux, separating layers, washing organic layer with water, drying over sodium sulfate, removing solvent in vacuo, purifying material by silica column chromatography using chloroform/cyclohexane (2:1) as eluent, and further purifying white solid product via recrystallization from toluene and subsequent distillation. Preferred Components: Compound of formula (I) is represented by formulae (Ia)-(If) provided that greater than or equal to 1 of compounds (Ia)-(If) contain formula (II). Group of formula (II) is represented by formula (IIA). Group of formula (II) is selected from group of formula (iii). Emitting layer contains silyl-substituted azadibenzofuran or azadibenzothiophene compound as host material in combination with a phosphorescent emitter.A1',A2'=group of formula (i);R89=H or group of formula (ii); andY15=O or S. SPECIFIC COMPOUNDS - 50 Compounds (I) are disclosed, e.g. (3-(benzofuro(3',2'-b)pyridin-8'-yl)phenyl)triphenylsilane (C-1); (3-(benzofuro(3',2'-d)pyrimidin-8'-yl)phenyl)triphenylsilane; (3-(benzofuro(2',3'-d)pyrimidin-6'-yl)phenyl)triphenylsilane; (3-(2'-tert.-butylbenzofuro(3',2'-d)pyrimidin-8'-yl)phenyl)triphenylsilane; and (3-(benzofuro(3',2'-d)pyrimidin-2'-yl)phenyl)triphenylsilane.    EXAMPLE - 8-bromobenzofuro(3,2-b)pyridine (1.25 g) and triphenyl-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)silane (2.33 g) were dissolved in toluene (100 ml) under argon. Ethanol (50 ml) was added, and solution was degassed. Potassium carbonate (K2CO3) (3.74 g) was dissolved in water (25 ml), and solution was degassed and added to reaction mixture. Tetrakis(triphenylphosphine)palladium(0) (Pd(Ph3)4) (175 mg) was added and heated up to 80 degrees C with stirring for 17 hours until thin layer chromatography (TLC) showed complete consumption of starting material. Reaction mixture was cooled to room temperature and poured into water (150 ml) and ethyl acetate (200 ml). Layers were separated, and aqueous layer was extracted with ethyl acetate (2x 100 ml). Combined organic layers were washed with water (100 ml) and dried over sodium sulfate (Na2SO4), and solvent was removed in vacuo. Crude product was dissolved in chloroform (100 ml) and 3% aqueous sodium cyanide (NaCN) solution (100 ml) was added. Mixture was heated under reflux for 2 hours. Layers were separated, and organic layer was washed with water (3x 100 ml) and dried over Na2SO4, and solvent was removed in vacuo. The material was purified by silica column chromatography using chloroform/cyclohexane (2:1) as eluent. (3-(benzofuro(3',2'-b)pyridin-8'-yl)phenyl)triphenylsilane (1.87 g, 74% yield) was obtained as white solid and further purified via recrystallization from toluene and subsequent distillation at 210 degrees C/4x 10-7 mbar.