The invention relates to novel mono-, oligo and polymers of thieno[2,3-b]thiophene, to their use as semiconductors or charge transport materials, in optical, electro-optical or electronic devices like LCDs, optical films, FETs or OFETs for TFT-LCDs and IC devices such as RFID tags, electroluminescent devices in flat panel displays or photovoltaic or sensor devices, and further relates to a FET, light emitting device or ID tag comprising the novel polymers.