Structural and electronic properties of crystalline, isomerically pure anthradithiophene derivatives

Anthradithiophene chromophores are found in many current high-performance organic semiconductors, even though these materials are typically synthesized as an inseparable mixture of syn and anti isomers. Recent syntheses of pure syn anthradithiophenes have shown no improvement in performance for the more homogeneous system, but similar studies on the pure anti isomer have not been reported. In this work, a simple protocol is described to prepare the pure anti isomer of fluorinated, functionalized anthradithiophenes, and perform detailed analysis of the intermolecular interactions in the crystal that yield increased density and closer chromophore contacts. Studies of the charge-transport properties of these pure isomers, compared to the isomeric mixtures, suggest that the benefit of isomer purity is not consistent; in the syn case, there was minimal difference between the pure isomer and the mixture, while for the anti isomer mobility improved nearly twofold. Analysis of disorder in the crystals suggests a reason for this difference in performance. Isolation of pure anti anthradithiophene derivatives sheds light on the intermolecular interactions that increase order in these materials. Strong hydrogen-fluorine interactions, along with an inversion center in the pure anti isomer, reduces disorder and decrease intermolecular spacing in these derivatives, yielding field-effect mobility higher than 6 cm² V^-1 s^-1 in spin-cast films.