Crystalline vs Liquid Crystalline Perylene Bisimides: Improved Electron Mobility via Substituent Alteration

Three solution processable n-type semiconducting perylene bisimides (PBI) with an unsymmetrical substitution pattern are evaluated in terms of their charge transport properties, morphology, and crystal structure. The nature of the substituents is varied from hydrophobic alkyl chains to hydrophilic oligoethyleneglycol (OEG) chains to control intermolecular interactions and to tune self-assembly properties of the compounds. A correlation of structure and morphology with charge transport properties is attempted. Bulk X-ray diffraction (XRD) data are indicative for a lamello-columnar packing motif in the case of PBI 1 and PBI 3 and a columnar hexagonal packing for PBI 2. Further, OEG chains induce liquid crystalline phases while the alkyl substituted compound is crystalline. In the amorphous state after film formation all three materials have a low electron mobility in the range of 10–5 cm2 V–1 s–1. After annealing in the ordered state the mobility of the liquid crystalline compounds increases by 2 orders of magnitude up to 7 × 10–3 cm2 V–1 s–1, while the mobility of the crystalline material decreases by a factor of 4.