NOVELTY - Polymer comprising one or more 7H-3,4-dithia-7-sila-cyclopenta(a)pentalene unit (I), is new.    USE - (I) is useful as charge transport, semiconducting, electrically conducting, photoconducting or light emitting material in an optical, electrooptical, electronic, electroluminescent or photoluminescent device, in a component of such a device, or in an assembly, where the device is organic field effect transistors, thin film transistors, organic LED, organic light emitting transistors, organic photovoltaic devices, organic photodetectors, organic solar cells, laser diodes, Schottky diodes, and photoconductors, the component is charge injection layers, charge transport layers, interlayers, planarizing layers, antistatic films, polymer electrolyte membranes, conducting substrates, conducting patterns, and the assembly is integrated circuits, radio frequency identification tags or security markings or security devices, flat panel displays or backlights, electrophotographic devices, electrophotographic recording devices, organic memory devices, sensor devices, biosensors and biochips (all claimed).    ADVANTAGE - (I) has excellent processibility for coating into thick layers, solubility in organic solvents, device performance and environmental stability including thermal and photo stability, high charge carrier mobility, external quantum and power conversion efficiency and low bandgap.    DETAILED DESCRIPTION - Polymer comprising one or more 7H-3,4-dithia-7-sila-cyclopenta(a)pentalene unit of formula (I), is new.    A = benzofused heteroaryl moiety comprising 1-6 heteroatoms (optionally substituted), which is divalent group of formulae (A1)-(A3);    Het = monocyclic moiety comprising at least one heteroatom in its ring (optionally substituted);    R1, R2 = H or halo, preferably H or F;    R3-R6 = H, halo, straight or branched or cyclic-1-30C-alkyl, where one or more non-adjacent CH2 groups are optionally replaced by -O-, -S-, -C(O)-, -C(S)-, -C(O)-O-, -O-C(O)-, -NR1a-, -SiR1aR2a-, -CF2-, -CHR1a=CR2a-, -CY1=CY2- or -C=C-, where O and/or S atoms are not linked directly to one another, and one or more H atoms are optionally replaced by F, Cl, Br, I or CN, or denote aryl, heteroaryl, aryloxy or heteroaryloxy with 4-20 ring atoms which is optionally substituted, preferably by halo or by one or more of the alkyl or cyclic alkyl groups;    Y1, Y2 = H, F, Cl or CN; and    R1a, R2a = H or 1-40C carbyl or hydrocarbyl (optionally substituted), preferably H or 1-12C-alkyl.    INDEPENDENT CLAIMS are included for:    (1) a mixture or polymer blend comprising (I) and one or more compounds or polymers having semiconducting, charge transport, hole/electron transport, hole/electron blocking, electrically conducting, photoconducting or light emitting properties;    (2) a formulation comprising (I), the mixtures or polymer blends, and one or more solvents, preferably organic solvents; and    (3) a distannyl monomer of formula (IV).    R10, R11 = H, Cl, Br, I, O-tosylate, O-triflate, O-mesylate, O-nonaflate, -Si(CH3)2F1, -Si(CH3)2F2, -O-SO2Z1, -B1(OZ2)2, -CZ3=C(Z3)2, -CCH, -CCSi(Z1)3, -ZnX1 or -Sn(Z4)3; either    Z1-Z4 = alkyl or aryl (both optionally substituted); or    Z2+Z2 = cyclic group; and    X1 = halo, preferably Cl, Br or I.