TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The indole-containing compound (I) is of formula (II)-(IV). Preferred Layer: The organic layer is light-emitting layer, hole injection layer or hole transport layer. Full Definitions:    Ar1,Ar2=6-60C aryl optionally substituted by substituent chosen from H, deuterium, halo, amino, nitrile, nitro, 1-20C alkyl, 1-20C alkoxy, 1-20C alkylamino, 1-20C alkylthiophene, 6-20C arylthiopene, 2-20C alkenyl, 2-20C alkynyl, 3-20C cycloalkyl, 6-60C aryl, 6-20C aryl substituted by deuterium, 8-20C arylalkenyl, silane, boron, germanium and 5-20C heterocyclyl, 5-60C heterocyclyl optionally substituted by substituent chosen from H, deuterium, halo, 1-20C alkyl, 2-20C alkenyl, 1-20C alkoxy, 8-20C arylamino, 6-60C aryl, 6-20C aryl substituted by deuterium, 8-20C arylalkyl, 8-20C arylalkenyl, 5-20C heterocyclyl, nitrile and acetylene, 6-30C aryloxy optionally substituted by substituent chosen from H, deuterium, halo, amino, nitrile, nitro, 1-20C alkyl, 2-20C alkenyl, 1-20C alkoxy, 3-30C cycloalkyl, 2-30C heterocycloalkyl, 6-60C aryl, 6-20C aryl substituted by deuterium and 3-60C heteroaryl, or 1-50C alkyl optionally substituted by substituent chosen from 1-20C alkyl, 2-20C alkenyl, 1-20C alkoxy, 6-20C aryl, 2-20C aryl substituted by deuterium, 8-20C arylalkyl, 8-20C arylalkenyl, 5-20C heterocyclyl, nitrile and acetylene;    R1,R2=H, deuterium, halo, nitro, nitrile, amino, 6-60C aryl optionally substituted by substituent chosen from H, deuterium, halo, amino, nitrile, nitro, 1-20C alkyl, 1-20C alkoxy, 1-20C alkylamino, 1-20C alkylthiophene, 6-20C arylthiopene, 2-20C alkenyl, 2-20C alkynyl, 3-20C cycloalkyl, 6-60C aryl, 6-20C aryl substituted by deuterium, 8-20C arylalkenyl, silane, boron, germanium and 5-20C heterocyclyl, 5-60C heteroaryl optionally substituted by substituent chosen from H, deuterium, halo, 1-20C alkyl, 2-20C alkenyl, 1-20C alkoxy, 8-20C arylamino, 6-60C aryl, 6-20C aryl substituted by deuterium, 8-20C arylalkyl, 8-20C arylalkenyl, 5-20C heterocyclyl, nitrile and acetylene and having O, N, and S, 6-60C arylamino optionally substituted by substituent chosen from halo, amino, nitrile, nitro, 1-20C alkyl, 2-20C alkenyl, 1-20C alkoxy, 3-30C cycloalkyl, 2-30C heterocycloalkyl, 6-60C aryl and 5-60C heteroaryl, 1-30C alkoxy optionally substituted by substituent chosen from H, deuterium, halo, amino, nitrile, nitro, 1-20C alkyl, 2-20C alkenyl, 1-20C alkoxy, 3-30C cycloalkyl, 2-30C heterocycloalkyl, 6-60C aryl, 6-20C aryl substituted by deuterium and 5-60C heteroaryl, 6-30C aryloxy optionally substituted by substituent chosen from H, deuterium, halo, amino, nitrile, nitro, 1-20C alkyl, 2-20C alkenyl, 1-20C alkoxy, 3-30C cycloalkyl, 2-30C heterocycloalkyl, 6-60C aryl, 6-20C aryl substituted by deuterium and 5-60C heteroaryl, or 1-50C alkyl optionally substituted by substituent chosen from 1-20C alkyl, 2-20C alkenyl, 1-20C alkoxy, 6-20C aryl, 6-20C aryl substituted by deuterium, 8-20C arylalkyl, 8-20C arylalkenyl, 5-20C heterocyclyl, nitrile and acetylene;    or R1+R2+neighboring group=(un)saturated aliphatic ring or hetero ring;    a=1-5;and    b=1-5.    SPECIFIC COMPOUNDS - 165 Indole-containing compounds are specifically claimed e.g. 1,2,1',2'-tetraphenyl-1H,1'H-(5,5')biindolyl of formula (Ia), 1'-naphthalen-1-yl-1,2,2'-triphenyl-1H,1'H-(5,5')biindolyl, 1-naphthalen-2-yl-2,1',2'-triphenyl-1H,1'H-(5,5')biindolyl, 1-biphenyl-4-yl-2,1',2'-triphenyl-1H,1'H-(5,5')biindolyl and 1-dibenzothiophen-2-yl-2,1',2'-triphenyl-1H,1'H-(5,5')biindolyl.