TECHNOLOGY FOCUS - ELECTRONICS - Preferred Composition: The organic electroluminescent device contains organic layer containing indoline derivative, arranged between the electrode (a) and electrode (b). Full definitions:    ring A=group of formula (i) or (ii);    X=O, S, NR11, CR12R13 or SiR14R15;    Y'=O, NR16, CR17R18 or SiR19R20;    R11-R20=H, 1-50C alkyl (optionally substituted by group (C')), 6-60C aryl (optionally substituted by group (A)), fluorenyl (optionally substituted by group (D')), 2-60C heterocyclyl containing at least one of O, N, S, Si or P and optionally substituted by group (B'), or -L1-N(Ar3)(Ar4);    or R12+R13 or R17+R18=optionally spiro compound;    R1-R4=H, halo, 6-60C aryl (optionally substituted by group (A)), 2-60C heterocyclyl containing at least one of O, N, S, Si or P and optionally substituted by group (B'), fluorenyl (optionally substituted by group (D')), 1-50C alkyl (optionally substituted by group (C')), 2-20C alkenyl (optionally substituted by D, halo, silanyl, cyano, 1-20C alkoxy, 1-20C alkyl, 2-20C alkenyl, 6-20C aryl (substituted with deuterium), 2-20C heterocyclyl, 3-20C cycloalkyl, 7-20C arylalkyl or 8-20C arylalkenyl), 1-30C alkoxy (optionally substituted by heavy hydrogen, halo, silanyl, 1-20C alkyl, 6-20C aryl substituted with deuterium, 2-20C heterocyclyl or 3-20C cycloalkyl) or -L2-N(Ar5)(Ar6);    Ar1,Ar2=6-60C aryl (optionally substituted by group (A)), 2-60C heterocyclyl containing at least one of O, N, S, Si or P and optionally substituted by group (B'), fluorenyl (optionally substituted by group (D')), 1-50C alkyl (optionally substituted by group (C')) or -L3-N(Ar7)(Ar8);    L,L1,L2,L3,L4=single bond, 6-60C aryl (optionally substituted by group (A)), fluorenyl (optionally substituted by group (D')), 2-60C heteroaryl, 3-60C cycloalkyl, 3-60C aliphatic group, 6-60C aryl (optionally substituted by group (A));    Ar3-Ar8=6-60C aryl, 2-60C heterocyclyl containing at least one of O, N, S, Si or P, 1-50C alkyl or fluorenyl;    group (A)=D, halo, silanyl, boronyl, germanyl, cyano, nitro, 1-20C alkylthio, 1-20C alkoxy, 1-20C alkyl, 2-20C alkenyl, 2-20C alkynyl, 6-20C aryl (substituted by D'), 2-20C heterocyclyl, 3-20C cycloalkyl, 7-20C arylalkyl or 8-20C arylalkenyl;    group (B')=D, halo, silanyl, cyano, nitro, 1-20C alkoxy, 1-20C alkyl, 2-20C alkenyl, 6-20C aryl (substituted by D), 2-20C heterocyclyl, 3-20C cycloalkyl, 7-20C arylalkyl or 8-20C arylalkenyl;    group (C')=group (B') (excluding D and 3-20C cycloalkyl);and    group (D')=D, halo, silanyl, cyano, 1-20C alkyl, 2-20C alkenyl, 6-20C aryl, 6-20C aryl (substituted by D), 2-20C heterocyclyl or 3-20C cycloalkyl.    SPECIFIC COMPOUNDS - 374 Indoline derivatives are specifically claimed e.g. N,N-diphenyl-4-(8H-thieno(2,3-b)indol-8-yl)aniline of formula (A), N-phenyl-N-(4-(8H-thieno(2,3-b)indol-8-yl)phenyl)naphthalen-1-amine, N-phenyl-N-(4-(8H-thieno(2,3-b)indol-8-yl)phenyl)naphthalen-2-amine, N-phenyl-N-(4-phenylphenyl)-4-(8H-thieno(2,3-b)indol-8-yl)aniline and N,9-diphenyl-N-(4-(8H-thieno(2,3-b)indol-8-yl)phenyl)-9H-carbazol-3-amine.