Novel Isoindigo-Based Organic Semiconductors End Capped with 1,1-Dicyanomethylene-3-Indanone: Effect of the Bromination and Position of Bromine Substituents on the Chemical–Physical and Electrical Properties

We report here on the synthesis and characterization of three novel isoindigo (II)-based organic semiconductors. The three dyes are based on an electron acceptor II core, symmetrically linked to two 3-octylthiophene donor rings; this common fragment, easily synthesizable, is end-capped with three different auxiliary electron acceptor groups, 1,1-Dicyanomethylene-3-Indanone (IDM) and two derivatives of it, bearing a bromine atom in position 5 or 6 of the IDM ring. The effect of the bromination and of the position of the bromine atom on the chemical–physical and electrical properties of the compounds were examined by means of thermal, optical, and electrochemical analysis; the electronic properties were investigated in more details at the DFT level. The novel compounds were used as active layers in organic field effect transistors: all the II derivatives were n-type unipolar semiconductors with electron mobilities ranging between 10−3 and 10−4 cm2/V∙s.