An organic semiconducting compound comprising the structure of formula (I): where Ar1, Ar2, Ar3 and Ar4 independently comprise monocyclic aromatic rings and at least one of Ar1, Ar2, Ar3 and Ar4 is substituted with at least one substituent X, which in each occurrence may be the same or different and is selected from the group consisting of (i) optionally substituted straight, branched or cyclic alkyl chains with 1 to 20 carbon atoms, alkoxy, amino, amido, silyl or alkenyl, or (ii) a polymerizable or reactive group selected from the group consisting of halogens, boronic acids, diboronic acids and esters of boronic acids and diboronic acids, alkylene groups and stannyl groups, and where Ar1, Ar2, Ar3 and Ar4 may each optionally be fused to one or more further rings. The organic semiconducting compound is used as an active layer in an organic semiconducting device such as a thin film transistor.