High mobility ambipolar charge transport in a cross-linked reactive mesogen at room temperature

By photochemically cross linking the molecules of a reactive end group functionalized calamitic liquid crystal (bis(heptylphenyl)-bithiophene-oxetane) in the smectic mesophase, an insoluble rigid molecular network is formed which remains structurally unchanged on cooling to room temperature. The charge transport is investigated by the time-of-flight method and the resulting material shows long-range (∼10 μm) ambipolar transport with nondispersive field independent hole mobility, μhole =0.016 cm2 V s and dispersive field dependent electron mobility, typically μelectron =0.028 cm2 V s (both at 4× 104 V cm-1 and at 15 °C). These desirable charge transport properties make this system a promising candidate for organic electronic applications, such as charge transport layers in organic light-emitting diodes and field effect transistors. © 2005 American Institute of Physics.