Novel liquid crystalline conjugated oligomers based on phenanthrene for organic thin film transistors

Abstract

Three thiophene/phenanthrene hybrid oligomers were synthesized and their liquid crystalline (LC) properties were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), temperature-dependent X-ray diffraction (XRD) and electron diffraction. Highly ordered LC phases with a broad temperature range were observed for all three oligomers probably owing to the absence of symmetry against the long axis of phenanthrene unit. Highly ordered smectic LC thin films were prepared by vacuum deposition and their organic thin film transistors (OTFTs) exhibited high mobilities up to 0.34 cm² V⁻¹s⁻¹. Solution processed films showed self-healing behaviors upon thermal annealing, and OTFTs prepared by solution drop casting showed mobilities up to 0.05 cm² V⁻¹s⁻¹. These results indicate that thiophene/phenanthrene hybrid oligomers are promising high mobility organic semiconductors for OTFTs.