Organic semiconductors have attracted considerable interest over the last decade due to an immense improvement in the performance of electronic devices based on these materials. This attention has mainly been focused on conjugated polymers and oligomers, as well as small molecules which can be utilized as active layers in devices such as field-effect transistors (FETs), [1,2] photovoltaic cells, [3] and light-emitting diodes.[4] An interesting group of materials with potential application as organic semiconductors in electronic devices are columnar discotics. [5,6] These mesogens consist of an aromatic core, which can be chemically modified by peripheral substitution (e.g., with alkyl chains), and self-assemble into one-dimensional (1D) columnar superstructures that then arrange in a two-dimensional (2D) lattice. The overlapping of the p orbitals of adjacent molecules within the columns ensures 1D intracolumnar charge-carrier transport. Another essential requirement for undisturbed 1D charge migration along the columns is a high degree of long-range order in the active layer which is deposited between the electrodes. [7] Local defects at domain boundaries in unoriented layers can trap charge carriers and significantly decrease the device performance. Thus, the development of appropriate processing techniques became an essential challenge for the fabrication of unperturbed long-range-oriented organic semiconductors. This close relationship between supramolecular structure and electronic properties has been investigated impressively for planar metallophthalocyanine (Pc) and metalloporphyrin derivatives, in which the charge-carrier mobility of the holes depends strongly on the processing technique.[8±11] For vacuum-deposited thin layers of phthalocyanine, the mobility varied from 10 ±4 cm 2 V ±1 s ±1 for nickel Pc [8] to 0.02 cm 2 V ±1 s ±1 for copper Pc. [9,10] Other processing techniques, such as solution deposition onto substrates with a friction-oriented poly(tetrafluoroethylene) (PTFE) layer [12] and the Langmuir±Blodgett (LB) method, require chemical substitution of Pc, which results in decreased mobility in comparison to samples prepared by vacuum deposition.[13]The history of discotic liquid-crystalline hexa-peri-hexabenzocoronene (HBC) derivatives as semiconductors is significantly shorter than that of phthalocyanines. Nevertheless, HBC derivatives have been successfully exploited in photovoltaic devices and field-effect transistors.[14] FETs were prepared by solution casting on substrates with the pre-oriented PTFE layer, resulting in uniaxial columnar order with an edge-on arrangement of the molecules.[15] The high supramolecular orientation was confirmed by field-effect anisotropy: the charge-carrier mobilities along the columns were significantly higher than in the perpendicular direction. [16] The high anisotropy of the charge-carrier mobility was demonstrated by flash-photolysis time-resolved microwave conductivity measurements.[17] The LB technique [18] and zone crystallization [19] have also been re...

Large-scale alignment of lamellae in thin films of diblock copolymers containing polyacrylonitrile and poly(n-butyl acrylate) was achieved by casting copolymer solution on a silicon substrate moved away at a constant speed from the casting nozzle (zone-casting). Grazing incidence small-angle X-ray scattering revealed that the lamellae, which were perpendicular to the substrate, were also aligned over macroscopic scale in the direction perpendicular to the casting direction. Such long-range ordered block copolymer films were then converted by pyrolysis into nanostructured carbons, with excellent preservation of lamellar morphology and orientation.

Uniaxially aligned, thin films of a discotic columnar thermotropic liquid crystalline material can be prepared by a simple solution zone-casting method, without the need for modified surfaces or traditional alignment techniques. Atomic force microscopy together with X-ray diffraction reveals single-crystalline-like order over several square centimeters, far exceeding the requirements for application of such films in organic molecular electronic devices such as field-effect transistors.