A polymer, comprising a repeating unit of formula -[Ar 3] c -[Ar 2] b -[Ar 1] a -Y(R 1) n1 (R 2) n2 -[Ar 1'] a' -[Ar 2'] b' -[Ar 3'] c' -, wherein a is 0, 1, 2, or 3, a' is 0, 1, 2, or 3; b is 0, 1, 2, or 3; b' is 0, 1, 2, or 3; c is 0, 1, 2, or 3; c' is 0, 1, 2, or 3; n1 is 1, or 2, n2 is 1, or 2, Y is a bivalent heterocyclic group, or ring system, which may optionally be substituted, Ar 1, Ar 1' Ar 2, Ar 2', Ar 3 and Ar 3' are independently of each other a C 6 -C 24 arylen group, which can optionally be substituted, or a C 2 -C 20 heteroarylen group, which can optionally be substituted; R 1 and R 2 in each occurrence are independently of each other hydrogen, C 5 -C 12 cycloalkyl, COR 38, C 1 -C 50 alkyl, C 3 -C 50 alkenyl, or C 3 -C 50 alkynyl, which can optionally be substituted one or more times with C 1 -C 12 alkoxy, halogen, C 5 -C 3 cycloalkyl, cyano, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, or a silyl group; and/or can optionally be further interrupted by one or more - O-, -S-, -NR 39 -, -CONR 39 -, -NR 39 CO-, -COO-, -CO-, or -OCO-, or a group of formula i is an integer from 1 to 18, R 70, R 71 and R 72 are independently of each other hydrogen, C 1 -C 50 alkyl, C 5 -C 12 cycloalkyl, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, C 2 -C 50 alkenyl or C 2 -C 50 alkynyl which can optionally be substituted one or more times with C 1 -C 12 alkoxy, halogen (especially F), C 5 -C 3 cycloalkyl, cyano, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, or a silyl group; and/or can optionally be further interrupted by one or more -O-, -S-, -NR 39 -, -CONR 39 -, -NR 39 CO-, -COO-, -CO-, or -OCO-; with the proviso that at least one of the substituents R 70, R 71 and R 72 is different from hydrogen; R 38 is C 1 -C 50 alkyl, C 2 -C 50 alkenyl, C 2 -C 50 alkynyl or C 1 -C 50 alkoxy, which can optionally be substituted one or more times with C 1 -C 12 alkoxy, halogen, C 5 -C 3 cycloalkyl, cyano, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, or a silyl group; and/or can optionally be further interrupted by one or more -O-, -S-, -NR 39 -, -CONR 39 -, -NR 39 CO-, -COO-, -CO-, or -OCO-, and R 39 is hydrogen, C 1 -C 25 alkyl, C 1 -C 18 haloalkyl, C 7 -C 25 arylalkyl, or C 1 -C 18 alkanoyl, with the proviso that at least one of R 1 and R 2 is a group of formula. a is 0, 1, 2, or 3, a' is 0, 1, 2, or 3; b is 0, 1, 2, or 3; b' is 0, 1, 2, or 3; c is 0, 1, 2, or 3; c' is 0, 1, 2, or 3; n1 is 1, or 2, n2 is 1, or 2, Y is a bivalent heterocyclic group, or ring system, which may optionally be substituted, Ar 1, Ar 1' Ar 2, Ar 2', Ar 3 and Ar 3' are independently of each other a C 6 -C 24 arylen group, which can optionally be substituted, or a C 2 -C 20 heteroarylen group, which can optionally be substituted; R 1 and R 2 in each occurrence are independently of each other hydrogen, C 5 -C 12 cycloalkyl, COR 38, C 1 -C 50 alkyl, C 3 -C 50 alkenyl, or C 3 -C 50 alkynyl, which can optionally be substituted one or more times with C 1 -C 12 alkoxy, halogen, C 5 -C 3 cycloalkyl, cyano, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, or a silyl group; and/or can optionally be further interrupted by one or more - O-, -S-, -NR 39 -, -CONR 39 -, -NR 39 CO-, -COO-, -CO-, or -OCO-, or a group of formula i is an integer from 1 to 18, R 70, R 71 and R 72 are independently of each other hydrogen, C 1 -C 50 alkyl, C 5 -C 12 cycloalkyl, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, C 2 -C 50 alkenyl or C 2 -C 50 alkynyl which can optionally be substituted one or more times with C 1 -C 12 alkoxy, halogen (especially F), C 5 -C 3 cycloalkyl, cyano, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, or a silyl group; and/or can optionally be further interrupted by one or more -O-, -S-, -NR 39 -, -CONR 39 -, -NR 39 CO-, -COO-, -CO-, or -OCO-; with the proviso that at least one of the substituents R 70, R 71 and R 72 is different from hydrogen; R 38 is C 1 -C 50 alkyl, C 2 -C 50 alkenyl, C 2 -C 50 alkynyl or C 1 -C 50 alkoxy, which can optionally be substituted one or more times with C 1 -C 12 alkoxy, halogen, C 5 -C 3 cycloalkyl, cyano, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, or a silyl group; and/or can optionally be further interrupted by one or more -O-, -S-, -NR 39 -, -CONR 39 -, -NR 39 CO-, -COO-, -CO-, or -OCO-, and R 39 is hydrogen, C 1 -C 25 alkyl, C 1 -C 18 haloalkyl, C 7 -C 25 arylalkyl, or C 1 -C 18 alkanoyl, with the proviso that at least one of R 1 and R 2 is a group of formula. i is an integer from 1 to 18, R 70, R 71 and R 72 are independently of each other hydrogen, C 1 -C 50 alkyl, C 5 -C 12 cycloalkyl, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, C 2 -C 50 alkenyl or C 2 -C 50 alkynyl which can optionally be substituted one or more times with C 1 -C 12 alkoxy, halogen (especially F), C 5 -C 3 cycloalkyl, cyano, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, or a silyl group; and/or can optionally be further interrupted by one or more -O-, -S-, -NR 39 -, -CONR 39 -, -NR 39 CO-, -COO-, -CO-, or -OCO-; with the proviso that at least one of the substituents R 70, R 71 and R 72 is different from hydrogen; R 38 is C 1 -C 50 alkyl, C 2 -C 50 alkenyl, C 2 -C 50 alkynyl or C 1 -C 50 alkoxy, which can optionally be substituted one or more times with C 1 -C 12 alkoxy, halogen, C 5 -C 3 cycloalkyl, cyano, C 6 -C 24 aryl, C 2 -C 20 heteroaryl, or a silyl group; and/or can optionally be further interrupted by one or more -O-, -S-, -NR 39 -, -CONR 39 -, -NR 39 CO-, -COO-, -CO-, or -OCO-, and R 39 is hydrogen, C 1 -C 25 alkyl, C 1 -C 18 haloalkyl, C 7 -C 25 arylalkyl, or C 1 -C 18 alkanoyl, with the proviso that at least one of R 1 and R 2 is a group of formula.