Dithienobenzo-thieno[3,2-b]thiophene-copolymers of the formula wherein: pi is wherein p, p' and u' independently are selected from -S-, -O-, -CH=, =CH-, -CR 6 = =CR 6 -, -C -, -C(C 2)-, -N=, =N-, -NH-, -NR 3 -, -SiR c =, =SiR c -, and -SiR 7 R c -; R 6, at each occurrence, is independently selected from a) halogen, b) -CN, c) -NO 2, d) N(R c) 2, e) -OR c, f) -C R c, g) -C OR c, h) -C N(R c) 2, i) a C 1-40 alkyl group, j) a C 2-40 alkenyl group, k) a C 2-40 alkynyl group, I) a C 1-40 alkoxy group, m) a C 1-40 alkylthio group, n) a C 1-40 haloalkyl group, o) a -Y-C 3-14 cycloalkyl group, p) a -Y-C 6-14 aryl group, q) a -Y-3-14 membered cycloheteroalkyl group, and r) a-Y-5-14 membered heteroaryl group R 1, R 2, R 3, at each occurrence, are independently H, a halogen, CN, a C 1-30 alkyl group, a C 2-30 alkenyl group, a C 1-30 haloalkyl group, a C 2-30 alkynyl group, a C 1-30 alkoxy group, a C -C 1-20 alkyl group, a C -OC 1-20 alkyl group, a Y-C 3-10 cyclo-alkyl group, a -Y-3-12 membered cycloheteroalkyl group, each optionally substituted with 1-5 substituents selected from a halogen, -CN, a C 1-6 alkyl group, a C 1-6 alkoxy group, and a C 1-6 haloalkyl group, -L-Ar 1, -L-Ar 1 -Ar 1, -L-Ar 1 -R 4, or -L-Ar 1 -Ar 1 - R 4 wherein: L, at each occurrence, is independently -O-, -Y-O-Y-, -S-, -S -, -Y-S-Y-, -C -, -NR c C -, -NR c -, -SiR c 2 -, -Y-[SiR c 2]-Y-, a divalent C 2-30 alkyl group, a divalent C 1-30 alkenyl group, a divalent C 1-30 haloalkyl group, or a covalent bond; wherein: R c, at each occurrence, is H, a C 1-20 alkyl group, or a -Y-C 6-14 aryl group; Ar 1, at each occurrence, is independently a C 6-14 aryl group or a 5-14 membered heteroaryl group, each optionally substituted with 1-5 substituents selected from a halogen, -CN, a C 1-6 alkyl group, a C 1-6 alkoxy group, and a C 1-6 haloalkyl group; and R 4, at each occurrence, is independently a C 1-20 alkyl group, a C 2-20 alkenyl group, a C 1-20 haloalkyl group, a C 1-20 alkoxy group, -L'-Ar 2, -L'-Ar 2 -Ar 2, -L'-Ar 2 -R 5, or -L'-Ar 2 -Ar 2 -R 5; wherein: L', at each occurrence, is independently -O-, -Y-O-Y-, -S-, -S -, -Y-S-Y-, -C -, -NR c C -, -NR c -, -SiR c 2 -, -Y-[SiR c 2]-Y-, a divalent C 1-20 alkyl group, a divalent C 1-20 alkenyl group, a divalent C 1-20 haloalkyl group, or a covalent bond; Ar 2, at each occurrence, is independently a C 6-14 aryl group or a 5-14 membered heteroaryl group, each optionally substituted with 1-5 substituents selected from a halogen, -CN, a C 1-6 alkyl group, a C 1-6 alkoxy group, and a C 1-6 haloalkyl group; R 5, at each occurrence, is a C 1-20 alkyl group, a C 2-20 alkenyl group, a C 1-20 haloalkyl group, or a C 1-20 alkoxy group; and Y, at each occurrence, is independently a divalent C 1-6 alkyl group, a divalent C 1-6 haloalkyl group, or a covalent bond; n = 0, 1, 2; and o = 5 - 1000. pi is wherein p, p' and u' independently are selected from -S-, -O-, -CH=, =CH-, -CR 6 = =CR 6 -, -C -, -C(C 2)-, -N=, =N-, -NH-, -NR 3 -, -SiR c =, =SiR c -, and -SiR 7 R c -; R 6, at each occurrence, is independently selected from a) halogen, b) -CN, c) -NO 2, d) N(R c) 2, e) -OR c, f) -C R c, g) -C OR c, h) -C N(R c) 2, i) a C 1-40 alkyl group, j) a C 2-40 alkenyl group, k) a C 2-40 alkynyl group, I) a C 1-40 alkoxy group, m) a C 1-40 alkylthio group, n) a C 1-40 haloalkyl group, o) a -Y-C 3-14 cycloalkyl group, p) a -Y-C 6-14 aryl group, q) a -Y-3-14 membered cycloheteroalkyl group, and r) a-Y-5-14 membered heteroaryl group R 1, R 2, R 3, at each occurrence, are independently H, a halogen, CN, a C 1-30 alkyl group, a C 2-30 alkenyl group, a C 1-30 haloalkyl group, a C 2-30 alkynyl group, a C 1-30 alkoxy group, a C -C 1-20 alkyl group, a C -OC 1-20 alkyl group, a Y-C 3-10 cyclo-alkyl group, a -Y-3-12 membered cycloheteroalkyl group, each optionally substituted with 1-5 substituents selected from a halogen, -CN, a C 1-6 alkyl group, a C 1-6 alkoxy group, and a C 1-6 haloalkyl group, -L-Ar 1, -L-Ar 1 -Ar 1, -L-Ar 1 -R 4, or -L-Ar 1 -Ar 1 - R 4 L, at each occurrence, is independently -O-, -Y-O-Y-, -S-, -S -, -Y-S-Y-, -C -, -NR c C -, -NR c -, -SiR c 2 -, -Y-[SiR c 2]-Y-, a divalent C 2-30 alkyl group, a divalent C 1-30 alkenyl group, a divalent C 1-30 haloalkyl group, or a covalent bond; R c, at each occurrence, is H, a C 1-20 alkyl group, or a -Y-C 6-14 aryl group; Ar 1, at each occurrence, is independently a C 6-14 aryl group or a 5-14 membered heteroaryl group, each optionally substituted with 1-5 substituents selected from a halogen, -CN, a C 1-6 alkyl group, a C 1-6 alkoxy group, and a C 1-6 haloalkyl group; and R 4, at each occurrence, is independently a C 1-20 alkyl group, a C 2-20 alkenyl group, a C 1-20 haloalkyl group, a C 1-20 alkoxy group, -L'-Ar 2, -L'-Ar 2 -Ar 2, -L'-Ar 2 -R 5, or -L'-Ar 2 -Ar 2 -R 5; L', at each occurrence, is independently -O-, -Y-O-Y-, -S-, -S -, -Y-S-Y-, -C -, -NR c C -, -NR c -, -SiR c 2 -, -Y-[SiR c 2]-Y-, a divalent C 1-20 alkyl group, a divalent C 1-20 alkenyl group, a divalent C 1-20 haloalkyl group, or a covalent bond; Ar 2, at each occurrence, is independently a C 6-14 aryl group or a 5-14 membered heteroaryl group, each optionally substituted with 1-5 substituents selected from a halogen, -CN, a C 1-6 alkyl group, a C 1-6 alkoxy group, and a C 1-6 haloalkyl group; R 5, at each occurrence, is a C 1-20 alkyl group, a C 2-20 alkenyl group, a C 1-20 haloalkyl group, or a C 1-20 alkoxy group; and Y, at each occurrence, is independently a divalent C 1-6 alkyl group, a divalent C 1-6 haloalkyl group, or a covalent bond; n = 0, 1, 2; and o = 5 - 1000.