Electron-Deficient Dihydroindaceno-Dithiophene Regioisomers for n-Type Organic Field-Effect Transistors

In this work, we wish to report the first member of a new family of organic semiconductors constructed on a meta dihydroindacenodithiophene core, that is, 2,2'-(2,8-dihexyl-4,6-dihydro-s-indaceno[1,2-b:7,6-b']dithiophene-4,6-diylidene)dimalononitrile (called meta-IDT(═C(CN)₂)₂). The properties of this molecule were studied in detail through a structure-properties relationship study with its regioisomer, that is, 2,2'-(2,7-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-4,9-diylidene)dimalononitrile (para-IDT(═C(CN)₂)₂) (see isomer structures in blue in Chart 2). The influence of the bridge functionalization was also investigated by comparison with their diketone analogues meta-IDT(═O)₂ and para-IDT(═O)₂. This study sheds light on the impact of regioisomerism on the electronic properties at the molecular level (electrochemistry, absorption spectroscopy, molecular modeling) and also on the supramolecular arrangement, and finally on the organic field-effect transistors (OFET) performances and stabilities. The significant effect of self-assembled monolayers of 4-(dimethylamino)benzenethiol grafted on the gold drain and source electrodes or of the use of flexible substrate (polyethylene naphtalate) instead of glass on the OFET performances and stabilities are also reported. In the light of these results (maximum mobility reaching 7.1 × 10^-2 cm² V^-1 cm^-1, high I_Don/I_Doff of 2.3 × 10⁷, and subthreshold swing of 1.2 V/dec), we believe that the present OFETs can be further used to construct electronic circuits.