NOVELTY - A silyl-substituted azadibenzofuran or azadibenzothiophene compound is new.    USE - A silyl-substituted azadibenzofuran or azadibenzothiophene compound for use as hole blocking layer materials, for electrophotographic photoreceptors, photoelectric converters, organic solar cells, switching elements, organic light emitting field effect transistors, image sensors, and dye lasers, and for organic electroluminescent device, electron transport layer, hole blocking layer, or emitting layer used for apparatus, such as stationary visual display units, mobile visual display units, illumination units, keyboards, items of clothing, furniture, and wallpaper (all claimed).    ADVANTAGE - The compounds provide improved efficiency, stability, manufacturability, or spectral characteristics of electroluminescent devices and ensure good efficiencies, good operative lifetimes, and high stability to thermal stress and low use and operating voltage of organic LEDs (OLEDs).    DETAILED DESCRIPTION - A silyl-substituted azadibenzofuran or azadibenzothiophene compound of formula (I) is new.    T=O or S;    B1=N or CR81;    B2=N or CR82;    B3=N or CR83;    B4=N or CR84;    B5=N or CR85;    B6=N or CR86;    B7=N or CR87;    B8=N or CR88;    R81-R88=H, CN, F, 1-25C alkyl optionally interrupted by D, 5-6C aryl optionally substituted by G, 2-5C heteroaryl optionally substituted by G, or formula (II);    o,p=0 or 1;    A1,A2=formulae (a) or (b);    R89=H or formulae (c) or (d);    Y',Y''=O or S;    B1'=N or CR81';    B2'=N or CR82';    B3'=N or CR83';    B4'=N or CR84';    B5'=N or CR85';    B6'=N or CR86';    B7'=N or CR87';    B8'=N or CR88';    R81'-R88'=H, CN, F, or 1-25C alkyl optionally interrupted by D;    R90-R92=Ph optionally substituted by 1-8C alkyl;    R93,R94=H or 1-25C alkyl;    D=-CC-, -COO-, -S-, -SO-, -SO2-, -O-, -NR65-, -SiR70R71-, -POR72-, -CR63=CR64-, or -CC-;    E=-CR69, -SR69, -NR65R66, -COR68, -COOR67, -CONR65R66, -CN, or F;    G=E, 1-18C alkyl, 6-24C aryl, 6-24C aryl substituted by F or 1-18C alkyl optionally interrupted by O, or 2-30C heteroaryl optionally substituted by F or 1-18C alkyl optionally interrupted by O;    R63,R64,R68=H, 6-18C aryl optionally substituted by 1-18C alkyl, or 1-18C alkoxy, or 1-18C alkyl optionally interrupted by -O-;    R65,R66=6-18C aryl optionally substituted by 1-18C alkyl or 1-18C alkoxy, 1-18C alkyl optionally interrupted by -O-, or R65 and R66 together form 5- or 6- membered ring;    R67,R69=6-18C aryl optionally substituted by 1-18C alkyl or 1-8C alkoxy, 1-18C alkyl optionally interrupted by -O-;    R70,R71=1-18C alkyl or 6-18C aryl optionally substituted by 1-18C alkyl; and    R72=1-18C alkyl or 6-18C aryl optionally substituted by 1-18C alkyl provided that greater than or equal to 1 of B1-B8 are N, less than or equal to 2 of B1-B4 are N, less than or equal to 2 of B5-B8 are N, and greater than or equal to 1 of R81-R88 are formula (II).    INDEPENDENT CLAIMS are included for:    (1) electron transport layer, hole blocking layer, or emitting layer comprising silyl-substituted azadibenzofuran or azadibenzothiophene compound; and    (2) production of compound of formula (Ia1) which involves reacting compound of formula HN=C(NH2)(R87) HCl with compound of formula (J) in solvent at elevated temperature to obtain compound of formula (Ia') and, if R83' is bromine or iodine, reacting compound (Ia') with compound of formula R83''-X12 in organic solvent in the presence of a palladium catalyst and base.    R83'=Br, I, H, CN, F, or 1-25C alkyl optionally interrupted by D;    X12=-B(OH)2, -B(OY1)2, or group of formula (iv);    Y1=1-10C alkyl;    Y2=2-10C alkylene;    Y13,Y14=H or 1-10C alkyl;    R83''=5-6C aryl optionally substituted by G, 2-5C heteroaryl optionally substituted by G, or formula (II); and    R87=H, 1-25C alkyl optionally interrupted by D, or formula (II) provided that R83 and/or R87 are formula (II).