A compound of general formula (IIb) or (IIc) wherein X 2 is CR 2 , X 4 is CR 4 , X 5 is CR 5 , X 6 is CR 6 , X 7 is CR 7 , X 8 is CR 8 , X 9 is CR 9 , X 10 is CR 10 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are H, R 2 is a group of formula -(L 1 ) o- (L 2 ) p- (L 3 ) q -(L 4 ) r -R 14 , wherein L 1 , L 2 , L 3 and L 4 are independently of each other selected from a C 6 -C 40 aryl group which is unsubstituted or substituted by at least one group E and a C 1 -C 24 heteroaryl group which is unsubstituted or substituted by at least one group E, and R 14 is independently of each other selected from H or a C 1 -C 25 alkyl group which unsubstituted or substituted by at least one group E and/or interrupted by at least one group D, o is 1, p is independently of each other 0 or 1, q is independently of each other 0 or 1 and r is independently of each other 0 or 1, D is independently of each other -CO-, -COO-, -S-, -SO-, -SO 2 -, -O-,-CR 15 =CR 16 -, -NR 17 -, -SiR 22 R 23 -, -POR 25 -, -C≡C-, E is independently of each other -OR 21 ,-SR 21 , -NR 17 R 18 , -COR 20 , -COOR 19 , -CONR 17 R 18 , -CN, -SiR 22 R 23 R 24 , POR 25 R 27 , halogen, a C 6 -C 60 aryl group which is unsubstituted or is substituted by at least one -F, - CF 3 , -CF 2 CF 3 , -CF 2 CF 2 CF 3 , -CF(CF 3 ) 2 , -(CF 2 ) 3 CF 3 or -C(CF 3 ) 3 , a C 1 -C 18 alkyl or a C 1 -C 18 alkyl group which is interrupted by at least one O, a C 1 -C 60 heteroaryl group which is unsubstituted or substituted by at least one -F, - CF 3 , -CF 2 CF 3 , -CF 2 CF 2 CF 3 , -CF(CF 3 ) 2 , -(CF 2 ) 3 CF 3 or -C(CF 3 ) 3 , R 15 and R 16 are independently of each other H, a C 6 -C 18 aryl group which is unsubstituted or substituted by at least one C 1 -C 18 alkyl group or at least one C 1 -C 18 alkoxy group, a C 1 -C 18 alkyl group or a C 1 -C 18 alkyl group which is interrupted by at least one O, R 17 and R 18 are independently of each other H, a C 6 -C 18 aryl group which is unsubstituted or substituted by at least one C 1 -C 18 alkyl group or at least one C 1 -C 18 alkoxy group, a C 1 -C 18 alkyl group or a C 1 -C 18 alkyl group, which is interrupted by at least one O, or R 17 and R 18 together form a five or six membered aliphatic, aromatic or heteroaromatic ring, R 19 is H, a C 6 -C 18 aryl group which is unsubstituted or substituted by at least one C 1 -C 18 alkyl group or at least one C 1 -C 18 alkoxy group, a C 1 -C 18 alkyl group or a C 1 -C 18 alkyl group, which is interrupted by at least one O, R 20 is H or a C 6 -C 18 aryl group which is unsubstituted or substituted by at least one C 1 -C 18 alkyl group or at least one C 1 -C 18 alkoxy group, a C 1 -C 18 alkyl group or a C 1 -C 18 alkyl group, which is interrupted by at least one O, R 21 is independently of each other H, a C 6 -C 18 aryl group which is unsubstituted or substituted by at least one C 1 -C 18 alkyl group or at least one C 1 -C 18 alkoxy group, a C 1 -C 18 alkyl group or a C 1 -C 18 alkyl group, which is interrupted by at least one O, R 22 , R 23 and R 24 are independently of each other H, a C 1 -C 18 alkyl group, a C 6 -C 18 aryl group which is unsubstituted or substituted by at least one C 1 -C 18 alkyl group, and R 25 and R 27 are independently of each other H, a C 1 -C 18 alkyl group, a C 6 -C 18 aryl group which is unsubstituted or substituted by at least one C 1 -C 18 alkyl group, a C 7 -C 25 aralkyl which is unsubstituted or substituted by at least one group E, a C 5 -C 12 cycloalkyl group which is unsubstituted or substituted by at least one group E. X 2 is CR 2 , X 4 is CR 4 , X 5 is CR 5 , X 6 is CR 6 , X 7 is CR 7 , X 8 is CR 8 , X 9 is CR 9 , X 10 is CR 10 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are H, <EOS>