Photoconducting discotic liquid crystals

Abstract

Photoconducting discotic liquid crystals (DLCs) as a relatively new class of photoconductors are attracting tremendous attention since they can form unique columnar nanostructures which exhibit remarkable mechanical, optical and electric properties. The history of photoconducting DLCs dates back to 1993 when Haarer and his coworkers reported that the discotic liquid crystalline hexapentyloxy triphenylene (HAT5) showed high charge carrier mobilities although the first DLCs were discovered in 1977 [1, 2]. Over the past decade, great progress has been made on these fascinating photoconducting DLCs. For liquid crystal display application, the conductivity of liquid crystals is detrimental. Interestingly, liquid crystals are intrinsically conductive. This conductivity arises from two origins: ionic contamination which is almost inevitable, and conductivity originating from the molecular structure and the phase of liquid crystal. The liquid crystals widely used in display application are composed of rod-like molecules in the nematic phase, resulting in low conductivity, i.e. at the order of ionic conduction. DLCs, on the other hand, typically have a much higher intrinsic conductivity than their display application counterpart. Instead of reducing DLC conductivity for use in aforementioned application, they are a good candidate for use in applications which require high conductivity. The disc-or plank-like structure of DLC molecule, in contrast with rod-like one, can facilitate face-to-face molecular stacking and lead to self-assembled superstructure by strong intermolecular interactions. Meanwhile, similar to liquid crystals comprised of conventional rod-like molecules, DLCs are also soft matter and are susceptible to external stimuli. © 2007 Springer.