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...

Functionalized, monocrystalline rutile TiO2 nanorods were prepared from TiCl4 in aqueous solution under acidic conditions in the presence of dopamine, followed by aging and hydrothermal treatment at 150 degrees C. The surface-bound organic ligand controls the morphology as well as the crystallinity and the phase selection of TiO2. The presence of monocrystalline rutile TiO2 was confirmed by X-ray powder diffraction and HRTEM investigations. The as-prepared nanorods are soluble in water at pH <3. The surface functionalization was analyzed by IR and 1H NMR, confirming the presence of dopamine on the surface. The surface amine groups can be tailored further with functional molecules such as dyes. Confocal laser scanning microscopy (CLSM) was used to characterize the binding of the fluorescent dye 4-chloro-7-nitrobenzofurazan (NBD) to the functionalized surface of the TiO2 nanorods.

Since the discovery of carbon nanotubes, [1] one-dimensional nanostructured materials have attracted great attention because of their various potential applications.[2] Porous alumina membranes exhibit straight nanoscale channels and have been COMMUNICATIONS

emissions of the nanometer-sized phosphors suggest good crystallinity, which is in good agreement with the results of XRD and TEM. A doping level of 20 mol-% Yb 3+ and 1 mol-% Er 3+gives the strongest luminescence. This method can be applied to other fluoride UC materials. Nanoparticles of around 50 nm diameter were synthesized in ethanol in the presence of EDTA with good dispersibility and high luminescence intensity and may be used as biological labeling material. ExperimentalAll chemicals were of analytical grade and were purchased from Beijing Chemical Corporation and used as received. Y 2 O 3 , Yb 2 O 3 , and Er 2 O 3 were dissolved in nitric acid. After the solution was dried, the nitrates were obtained. Water, acetic acid, and sodium ethoxide were used to dissolve the nitrates. Sodium fluoride and sodium acetate were used to provide sodium ions. Hydrogen ammonium fluoride was used as a fluorine source. After stirring, the solutions were transferred to Teflon-lined autoclaves and heated to 140±200 C for 12±24 h. EDTA and CTAB were used to control the size and morphology of the products.The structure and phase purity of the as-prepared phosphors were characterized by powder XRD using a Bruker D8 Advance X-ray diffractometer with monochromatic Cu Ka radiation (k = 1.541781 ). The size and morphology of the products were further examined using scanning electron microscopy (JEOL JSM-6700F) and TEM (JEOL JEM-1200EX) operating at an accelerating voltage of 120 kV. UC luminescent spectra were recorded on an Hitachi F-4500 fluorescence spectrophotometer with a 2.0 mW 980 nm exciting laser beam. The investigation of extremely small crystalline particles like fluorescent quantum dots has drawn a lot of attention [1] because the materials properties are altered at a dimension of about 10 nm and below. In the case of liquid crystals (LCs), differences between the bulk material and material in confined geometries have already been found for larger dimensions (about 100 nm).[2] This happens because LCs are soft' materials and the energy responsible for long-range orientational order is very small. Therefore, the substrate has an influence on the liquid-crystalline phase up to a distance, L, which may reach several hundred nanometers. [3,4] Investigation of LCs confined in pores smaller than L provide, in principle, information on the interfacial properties of these LCs. As a result of these investigations it is known that restricted geometries have a significant effect on the order, structure, and phase transition of nematic LCs. In the case of ferroelectric liquid crystals (FLCs), for example, it is known that smectic C and smectic A phases are present in silica porous glasses with 100 nm diameter pores. [4,5] The phase-transition temperature between these phases is reduced by about 15 C compared with the bulk value. The Goldstone as well as the soft mode, which proves the polar order, is found in these pores, but the rotational viscosity associated with the soft mode is COMMUNICATIONS

The self-organization of two polycyclic aromatic hydrocarbons with different aromatic core sizes, dodecylphenyl-substituted hexa-peri-hexabenzocoronene and an extended disk consisting of 96 carbon atoms 6-fold-alkyl-substituted, on the surface from solution has been investigated. Highly ordered surface layers of both materials could be obtained by the zone-casting technique, despite an apparently low self-organization in drop-cast films. The zone-cast films revealed high macroscopic uniaxial orientation of the columns with a molecular edge-on arrangement on the glass support as confirmed by polarized optical microscopy, UV-vis measurements in polarized light, high-resolution transmission electron microscopy, and X-ray diffraction. Electron diffraction indicated a high intracolumnar periodicity of the molecules, but a low intercolumnar correlation of the disks due to the increased molecular dynamics in the liquid crystalline phase.