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 crystal phase is 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 weak, transient biaxial alignment can be induced under specific thermal and mechanical conditions. In sandwich cells, TOF electron mobilities of up to 2.2 × 10‾² cm² V‾¹ s‾¹ are obtained, which are the highest found to date for nematic materials. The latter is attributed to the special self-assembly of the biaxial, roof-shaped mesogens, which favors the contacts between the aromatic units, which is confirmed by X-ray scattering, modeling, 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.