The invention relates to novel organic semiconducting compounds, which are small molecules or conjugated polymers, containing one or more isoindigo or thienoisoindigo based polycyclic units, to methods for their preparation and educts or intermediates used therein, to compositions, polymer blends and formulations containing them, to the use of the compounds, compositions and polymer blends as organic semiconductors in, or for the preparation of, organic electronic (OE) devices, especially organic photovoltaic (OPV) devices, organic photodetectors (OPD), Perovskite based solar cells, organic field effect transistors (OFET) and organic light emitting diodes (OLED), and to OE, OPV, OPD, OFET and OLED devices comprising these compounds, compositions or polymer blends.