High Electron Charge Carrier Mobility in the Nematic Phase of a Roof-Shaped Nematogen with Optimum Molecular Biaxiality

A roof-shaped molecule forming exclusively a nematic liquid crystals phase has been prepared based on a lead structure. The aspect ratio is designed to be almost optimum with respect to the molecular biaxiality. A broad nematic phase over more than 100 K is observed in which a transient biaxiality can be induced. In sandwich cells, TOF electron mobilities of up to 10-2 cm2V-1s-1are obtained, which are the highest found to date for nematic materials. The latter is attributed to the special self-assembly of the roof-shaped mesogens favouring the contacts between the aromatic units, which is confirmed by X-ray scattering, modelling and X-ray scattering simulation. The material is responsive to the applied electric field which results in the anomalous negative field dependence of the charge carrier mobilities.