NOVELTY - Oligomeric or polymeric compounds (I) comprising substituted 3,6-di-thiophen-2-yl-2,5-dihydro-pyrrolo(3,4-c)pyrrole-1,4-dione repeating units (Ia) in its backbone are new.    USE - (I) are useful: in an electronic, optical or optoelectronic device (claimed); as organic semiconductors in organic and hybrid optical devices including photovoltaic cells, light emitting diodes, light emitting transistors and field effect transistors; to prepare either p-type (donor or hole-transporting), n-type (acceptor or electron-transporting), or ambipolar semiconductor materials.    ADVANTAGE - (I): have solution-processability and/or good stability in ambient conditions; provide high power conversion efficiency, fill factor, open circuit voltage, field-effect mobility, on/off current ratios, and/or air stability when used in photovoltaic cells or transistors; have good solubility in common solvents enabling device fabrication through solution processes; exhibit semiconductor behavior including high carrier mobility and/or good current modulation characteristics in a field-effect device, optimized light absorption/charge separation in a photovoltaic device and/or charge transport/recombination/light emission in a light-emitting device; exhibit properties including excellent charge transport characteristics in ambient conditions, optimized optical absorption, chemical stability, low-temperature processability and processing versatility; and can be processed into very efficient solar cells without a thermal annealing step, and thus provides time- and cost-saving benefits.    DETAILED DESCRIPTION - Oligomeric or polymeric compounds (I) comprising substituted 3,6-di-thiophen-2-yl-2,5-dihydro-pyrrolo(3,4-c)pyrrole-1,4-dione repeating units of formula (Ia) in its backbone are new.    Ar1 = monocyclic aryl or heteroaryl;    R5 = 1-40C alkyl, 2-40C alkenyl, 2-40C alkynyl or 1-40C haloalkyl (all optionally substituted by 1-10 substituents comprising halo, -CN, NO2, OH, -NH2, -NH(1-20C alkyl), -N(1-20C alkyl)2, -S(O)2OH, -CHO, -C(O)-1-20C alkyl, -C(O)OH, -C(O)-O1-20C alkyl, -C(O)NH2, -C(O)NH-1-20C alkyl, -C(O)N(1-20C alkyl)2, -O1-20C alkyl, -SiH3, -SiH(1-20C alkyl)2, -SiH2(1-20C alkyl) or -Si(1-20C alkyl)3, and at least one non-adjacent -CH2- are replaced by -O-, -S-, -NH-, -N(1-20C alkyl)-, -C(O)-, -C(O)O- or -Si(1-20C alkyl)2) or H;    R6, R7 = H or -L-R;    L = O, S or covalent bond;    R = 1-40C alkyl; and    A = 5,5'-(thieno(3,2-b)thiophen-2,5-diyl), 5,5'-(thieno(2,3-b)thiophen-2,5-diyl), 5,5'-(benzo(b)thiophen-2,5-diyl), 5,5'-(benzo(b)thiophen-2,6-diyl), 5,5'-(thieno(3,2-b)thiophen-2,5-diyl) moiety of formula (a) (preferred), 5,5'-(thieno(3,2-b)thiophen-2,5-diyl) moiety of formula (b), 5,5'-(thieno(2,3-b)thiophen-2,5-diyl) moiety of formula (c), 5,5'-(thieno(2,3-b)thiophen-2,5-diyl) moiety of formula (d), 5,5'-(benzo(b)thiophen-2,5-diyl) moiety of formula (e), 5,5'-(benzo(b)thiophen-2,5-diyl) moiety of formula (f), 5,5'-(benzo(b)thiophen-2,5-diyl) moiety of formula (g) or 5,5'-(benzo(b)thiophen-2,5-diyl) moiety of formula (h).    INDEPENDENT CLAIMS are also included for:    (1) an electronic, optical or optoelectronic device comprising: a first electrode; a second electrode; and a semiconductor component comprising (I) disposed between the first electrode and the second electrode;    (2) substituted 3,6-di-thiophen-2-yl-2,5-dihydro-pyrrolo(3,4-c)pyrrole-1,4-dione compounds of formula (III); and    (3) preparing (III) comprising reacting a succinic acid ester with substituted thiophene-2-carbonitrile compounds of formula (IV).    L1 = O, S, Se, NR10 or covalent bond; and    R10 = H or 1-40C alkyl.