TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation: No general preparation given. Preferred Composition: The emitting layer comprises benzimidazolo-benzothiazole derivative compound as host material in combination with phosphorescent emitter. Full Definitions:    Y1,Y2=1-25C alkyl (optionally substituted by E and/or interrupted by D'), or 6-24C aryl, 2-30C heteroaryl or 7-25C aralkyl (all optionally substituted by G);    c,d=0 or 1;    R1,R6=1-25C alkyl (optionally substituted by E and/or interrupted by D'), -(A1)o(A2)p-(A3)q-(A4)r-R16, or 6-24C aryl or 2-30C heteroaryl (both optionally substituted by G);    a,b=0-3;    o,p,q,r=0 or 1;    A1-A4=6-24C arylenyl, or 2-30C heteroarylenyl (both optionally substituted by G);    R16=H, -NR10R11, -Si(R12)(R13)(R14), or 6-24C aryl or 2-30C heteroaryl (both optionally substituted by G);    R10,R11=6-24C aryl or 2-30C heteroaryl (both optionally substituted by G);    R12-R14=1-25C alkyl (optionally substituted by E and/or interrupted by D'), or 6-24C aryl or 2-30C heteroaryl (both optionally substituted by G);    D'=-CO-, -COO-, -S-, -SO-, -SO2-, -O-, -NR65-, -SiR70R71-, -POR72-, -CR63=CR64- or -CC-;    E=-OR69, -SR69, -NR65R66, -COR68, -COOR67, -CONR65R66, -CN or F;    G=E, or 1-18C alkyl, 6-24C aryl (optionally substituted by F or 1-18C alkyl (optionally substituted by F and/or interrupted by O)), or 2-30C heteroaryl (optionally substituted by F, 1-18C alkyl (optionally interrupted by O) or -Si(R12')(R13')(R14'));    R12'-R14'=1-25C alkyl optionally interrupted by O, or 6-14C aryl or 2-10C heteroaryl (both optionally substituted by 1-18C alkyl);    R63,R64=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), or 1-18C alkyl (optionally interrupted by -O-);    or R65+R66=5 or 6-membered ring;    R67=6-18C aryl (optionally substituted by 1-18C alkyl or 1-18C alkoxy), or 1-18C alkyl (optionally interrupted by -O-);    R68=H, 6-18C aryl (optionally substituted by 1-18C alkyl or 1-18C alkoxy), or 1-18C alkyl (optionally interrupted by -O-);    R69=6-18C aryl (optionally substituted by 1-18C alkyl or 1-18C alkoxy), or 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.    (i) At least one of R1 and R6 is -(A1)0-(A2)p-(A3)q-(A4)r-R16; and (ii) R16 is not H, when o, p, q and r are 0. Preferred Definitions:    -(A1)0-(A2)p-(A3)q-(A4)r-R16=132 groups chosen from group of formula (i)-(xx).    SPECIFIC COMPOUNDS - 15 Benzimidazolo-benzothiazole derivatives are disclosed, e.g. 5-(1,8,10-triazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaen-8-yl)-8-thia-1,10-diazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaene of formula (Ia), 5-(9H-carbazol-9-yl)-8-thia-1,10-diazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaene, 5-(3-(1,8,10-triazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaen-8-yl)-9H-carbazol-9-yl)-8-thia-1,10-diazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaene, 14-(1,8,10-triazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaen-8-yl)-8-thia-1,10-diazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaene and 4,14-bis(9H-carbazol-9-yl)-8-thia-1,10-diazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaene.    EXAMPLE - 4.8 g 6H-Benzimidazolo(1,2-a)benzimidazole, 5.1 g 2-bromo-4-fluoro-2-nitrobenzene and 3.68 g potassium carbonate were stirred in 63 ml dimethyl sulfoxide under argon at 100 degrees C for 1 hour, cooled to 20 degrees C, and poured into 240 ml water. The resultant product was filtered, washed with water, and 4.91 mmol product was reacted with 0.81 g 1,3-dihydrobenzimidazole-2-thione and 4 g cesium carbonate in 16 ml dimethyl sulfoxide with stirring at 130 degrees C for 1 hour and at 170 degrees C for 4 hours. The reaction mixture was diluted with water, product was filtered off and decocted in 20 ml ethanol, to obtain 5-(1,8,10-triazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaen-8-yl)-8-thia-1,10-diazatetracyclo(7.7.0.02,7.011,16)hexadeca-2(7),3,5,9,11(16),12,14-heptaene.