The present invention relates to novel compounds of the formula (I) wherein R1 and R1′ independently of each other are H or a substituent, halogen or SiR6R4R5; R2 and R2′ may be the same or different and are selected from C1-C25alkyl, C3-C12-cycloalkyl, C2-C25alkenyl, C2-C25alkynyl, C4-C25aryl, C5-C25alkylaryl or C5-C25aralkyl, each of which is unsubstituted or substituted, and under conditions as defined in claim 1, R2 and/or R2′ may also be halogen or hydrogen; X is a divalent linking group selected from formula (Ia) and formula (Ib); Y and Y′ independently are selected from formula (Ic), formula (Id), formula (Ie), formula (If), formula (Ig); n and p independently range from 0 to 6; where further symbols are as defined in claim 1, and to corresponding oligomers and (co)polymers. The compounds according to the invention are useful as semiconductors and have excellent solubility in organic solvents and excellent film-forming properties. In addition, high efficiency of energy conversion, excellent field-effect mobility, good on/off current ratios and/or excellent stability can be observed, when the polymers according to the invention are used in organic field effect transistors, organic photovoltaics (solar cells) and photodiodes.