NOVELTY - Polymer (I) comprising at least a benzo(1,2-b;4,5-b')dithiophene structural unit (II), is new.    USE - (I) is useful in organic electronic devices, preferably organic electroluminescent devices, polymeric electroluminescent devices, organic integrated circuits, organic field-effect transistors, organic thin-film transistors, organic light-emitting transistors, organic solar cells, organic optical detectors, organic photoreceptors, organic field-quench devices, light-emitting electrochemical cells or organic laser diodes (claimed).    ADVANTAGE - (I) exhibits high stability, high efficiency, small operation voltage and long service life.    DETAILED DESCRIPTION - Polymer (I) comprising at least a benzo(1,2-b;4,5-b')dithiophene structural unit of formula (II), is new.    X, Y1 = (hetero)aryl ring, in which one or more H atoms of the ring is optionally replaced by R, where additionally one or both X or Y1 is optionally R, preferably phenyl, naphthyl, anthracenyl, phenanthrenyl, pyrenyl, chrysenyl, perylenyl, fluoranthenyl, naphthacenyl, pentacenyl, benzpyrenyl, biphenyl, biphenylenyl, terphenyl, terphenylenyl, fluorenyl, spirobifluorenyl, dihydrophenanthrenyl, dihydropyrenyl, tetrahydropyrenyl, cis- or trans-indenofluorenyl, truxenyl, isotruxenyl, spirotruxenyl, spiroisotruxenyl, furanyl, benzofuranyl, isobenzofuranyl, dibenzofuranyl, thiophenyl, benzothiophenyl, isobenzothiophenyl, dibenzothiophenyl, pyrrolyl, indolyl, isoindolyl, carbazolyl, pyridinyl, quinolinyl, isoquinolinyl, acridinyl, phenanthridinyl, benzo-5,6-quinolinyl, benzo-6,7-quinolinyl, benzo-7,8-quinolinyl, phenothiazinyl, phenoxazinyl, pyrazolyl, indazolyl, imidazolyl, benzimidazolyl, naphthimidazolyl, phenanthrimidazolyl, pyridimidazolyl, pyrazinimidazolyl, quinoxalinimidazolyl, oxazolyl, benzoxazolyl, naphthoxazolyl, anthroxazolyl, phenanthroxazolyl, isoxazolyl, 1,2-thiazolyl, 1,3-thiazolyl, benzothiazolyl, pyridazinyl, benzopyridazinyl, pyrimidinyl, benzpyrimidinyl, quinoxalinyl, 1,5-diazaanthracenyl, 2,7-diazapyrenyl, 2,3-diazapyrenyl, 1,6-diazapyrenyl, 1,8-diazapyrenyl, 4,5-diazapyrenyl, 4,5,9,10-tetraazaperylenyl, pyrazinyl, phenazinyl, phenoxazinyl, phenothiazinyl, fluorubinyl, naphthyridinyl, azacarbazolyl, benzocarbolinyl, phenanthrolinyl, 1,2,3-triazolyl, 1,2,4-triazolyl, benzotriazolyl, 1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, 1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl, 1,3,4-thiadiazolyl, 1,3,5-triazinyl, 1,2,4-triazinyl, 1,2,3-triazinyl, tetrazolyl, 1,2,4,5-tetrazinyl, 1,2,3,4-tetrazinyl, 1,2,3,5-tetrazinyl, purinyl, pteridinyl, indolizinyl, benzothiadiazolyl, benzanthrenyl, benzanthracenyl, rubicenyl or triphenylenyl (all optionally substituted by 1-12C-alkyl or 1-12C-alkoxy, preferably 6-12C-alkyl, 6-12C-alkoxy and/or (hetero)aryl or (hetero)aryloxy);    R = 1-40C-alkyl, 1-40C-alkoxy, 1-40C-thioalkoxy, cyclic 3-40C-alkyl, 3-40C-alkoxy, 3-40C-thioalkoxy (all optionally substituted by R1), D, F, Cl, Br, I, N(Ar1)2, C(=O)Ar1, P(=O)Ar12, S(=O)Ar1, S(=O)2Ar1, CR1=CR1Ar1, CN, NO2, Si(R1)3, B(OR1)2 or OSO2R1, where one or more non-adjacent CH2 groups are optionally replaced by R1C=CR1, C?=C, Si(R1)2, Ge(R1)2, Sn(R1)2, C=O, C=S, C=Se, C=NR1, P(=O)(R1), SO, SO2, NR1, O, S or CONR1 and one or more H atoms are optionally replaced by F, Cl, Br, I, CN or NO2;    Ar1 = (hetero)aryl; and    R1 = H, 1-20C-aliphatic hydrocarbon or 6-20C-aromatic hydrocarbon.    Where: the H atoms in one or both of the thiophene rings are optionally replaced by R. INDEPENDENT CLAIMS are included for:    (1) a blend comprising (I) and further a polymer (different from (I)), oligomer, dendrimer or a low molecular compound;    (2) a formulation comprising (I) and/or a solvent; and    (3) an organic electronic device comprising at least a layer containing (I).