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,