Columnar Mesomorphism in a Methylthio-Decorated Triindole for Enhanced Charge Transport.

We report a semiconducting triindole-based discotic liquid crystal () functionalized with six -methylthiophenyl groups at its periphery. While initially a crystalline solid at room temperature, transitions to a columnar hexagonal mesophase upon heating and retains this supramolecular organization upon subsequent cooling, despite having only three flexible alkyl chains attached to the core's nitrogens. The incorporation of methylthio groups effectively hinders tight molecular packing, stabilizing the columnar arrangement of this disk-shaped molecule.

Effect of Hydrogen Bonding and Chirality in Star-Shaped Molecules with Peripheral Triphenylamines: Liquid Crystal Semiconductors and Gels.

Organic semiconductors with well-defined architectures pose a suitable alternative to amorphous silicon-based inorganic semiconductors. Encouraged by the development of organic semiconductors based on columnar liquid crystals, herein, we report on a family of -symmetric star-shaped mesogens based on triphenylamine (TPA), a functional unit with strong electron donor character. Highly stable columnar phases with high hole mobility values were obtained out of this nonplanar functional unit, and this was achieved by using flexible amide spacers to join the TPA units to a tris(triazolyl)triazine (T) star-shaped core, allowing the formation of intermolecular hydrogen bonds.

Photoconductive Properties and Electronic Structure in 3,5-Disubstituted 2-(2'-Pyridyl)Pyrroles Coordinated to a Pd(II) Salicylideneiminate Synthon.

The synthesis and the electrochemical, photophysical, structural, and photoconductive properties of three new heteroleptic Pd(II) complexes with various 3',5'- disubstituted-2-(2'-pyridil) pyrroles H(N^N) as coordinated ligands are reported. The coordination of the metal center was completed by a functionalized Schiff base H(O^N) used as an ancillary ligand. The [(N^N)Pd(O^N)] complexes showed highly interesting photoconductive properties which have been correlated to their electronic and molecular structures.

Charge Mobility in Discotic Liquid Crystals.

Discotic (disk-shaped) molecules or molecular aggregates may form, within a certain temperature range, partially ordered phases, known as discotic liquid crystals, which have been extensively studied in the recent past. On the one hand, this interest was prompted by the fact that they represent models for testing energy and charge transport theories in organic materials. However, their long-range self-assembling properties, potential low cost, ease of processability with a variety of solvents and the relative ease of tailoring their properties via chemical synthesis, drove the attention of researchers also towards the exploitation of their semiconducting properties in organic electronic devices.

Striking Increase in Hole Mobility upon Metal Coordination to Triphenylene Schiff Base Semiconducting Multicolumnar Mesophases.

This paper reports the synthesis, liquid-crystal behavior, and charge-transport properties in the mesophase of triphenylene Schiff bases and their copper(II), nickel(II), and oxovanadium(IV) complexes. The thermal and electronic properties of the Schiff bases are modulated by coordination to the corresponding metal moieties, which have the ability to self-assemble into linear structures and help the alignment of the triphenylene columns. This produces two kinds of electronically nonconnected columnar regions, one purely organic and one more inorganic.

Inspecting the Electronic Architecture and Semiconducting Properties of a Rosette-Like Supramolecular Columnar Liquid Crystal.

Computational and experimental studies unravel the structural and electronic properties of a novel supramolecular liquid crystal built through a hierarchical assembly process resulting in an H-bonded melamine rosette decorated with peripheral triphenylenes. The six-fold symmetry of the mesogen facilitates the formation of a highly organized hexagonal columnar mesophase stable at room temperature. X-ray diffraction and electron density maps confirm additional intra- and intercolumn segregation of functional subunits, and this paves the way for 1D charge transport.

Making Coaxial Wires Out of Janus Dendrimers for Efficient Charge Transport.

Highly conductive coaxial supramolecular wires are prepared by using a new family of dendrimers that combines two rigid aromatic parts and two flexible aliphatic parts. The two external regions consist of a promesogenic block based on a third generation Percec-type dendron with four terminal dodecyloxy alkyl chains, whereas the two internal regions are formed by one, two, or three carbazole units bearing flexible spacers. These functional dendrimers self-organize in columnar liquid crystal phases with a strong coaxial segregation within each column.

High-Mobility Self-Assembling Truxenone-Based n-Type Organic Semiconductors.

The synthesis, self-assembly, and semiconducting properties of a series of disk-like truxenone derivatives, functionalized with three peripheral long alkyl chains, either directly attached or distanced by linking phenyl or ethynyl groups, are reported. The strategy of distancing the alkyl chains from the central aromatic cores induces in these discotics well-ordered columnar assemblies and has a favorable effect on their charge-carrier mobility. Electron mobility values above 1 cm  V  S were determined for a truxenone functionalized with three peripheral decynyl chains by means of the space charge-limited current technique.

Not Only Columns: High Hole Mobility in a Discotic Nematic Mesophase Formed by Metal-Containing Porphyrin-Core Dendrimers.

We report a new family of multifunctional liquid-crystalline porphyrin-core dendrimers that have coumarin functional groups around the porphyrin core. Porphyrin metalation strongly affects the photophysical properties, and therefore Zn and Cu derivatives have also been prepared. All the synthesized dendrimers form a nematic discotic mesophase.

Mobility versus Alignment of a Semiconducting π-Extended Discotic Liquid-Crystalline Triindole.

The p-type semiconducting properties of a triphenylene-fused triindole mesogen, have been studied by applying two complementary methods which have different alignment requirements. The attachment of only three flexible alkyl chains to the nitrogen atoms of this π-extended core is sufficient to induce columnar mesomorphism. High hole mobility values (0.

H-Bonded Donor-Acceptor Units Segregated in Coaxial Columnar Assemblies: Toward High Mobility Ambipolar Organic Semiconductors.

A novel approach to ambipolar semiconductors based on hydrogen-bonded complexes between a star-shaped tris(triazolyl)triazine and triphenylene-containing benzoic acids is described. The formation of 1:3 supramolecular complexes was evidenced by different techniques. Mesogenic driving forces played a decisive role in the formation of the hydrogen-bonded complexes in the bulk.

Electropolymerized highly photoconductive thin films of cyclopalladated and cycloplatinated complexes.

The complete characterization of novel electropolymerizable organometallic complexes is presented. These are newly synthesized cyclometalated complexes of general formula (PPy)M(O ∧ N)(n) (H(PPy) = 2-phenylpyridine, M = Pd(II) or Pt(II), H(O ∧ N)(n) = Schiff base). Polymeric thin films have been obtained from these complexes by electropolymerization of the triphenylamino group grafted onto the H(O ∧ N)(n) ancillary ligand.

Functional carbazole liquid-crystal block codendrimers with optical and electronic properties.

The synthesis and characterisation of a family of block codendrimers consisting of highly versatile mesogenic and carbazole-containing 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) dendrons are reported. The liquid-crystal behaviour was investigated by means of differential scanning calorimetry, polarised-light optical microscopy and X-ray diffraction. Depending on the chemical structure of the constituent dendrons, the codendrimers show lamellar or columnar mesophases.

Multifunctional supramolecular dendrimers with an s-triazine ring as the central core: liquid crystalline, fluorescence and photoconductive properties.

Novel liquid crystal (LC) dendrimers have been synthesised by hydrogen bonding between an s-triazine as the central core and three peripheral dendrons derived from bis(hydroxymethyl)propionic acid. Symmetric acid dendrons bearing achiral promesogenic units have been synthesised to obtain 3:1 complexes with triazine that exhibit LC properties. Asymmetric dendrons that combine the achiral promesogenic unit and an active moiety derived from coumarin or pyrene structures have been synthesised in order to obtain dendrimers with photophysical and electrochemical properties.

UV/Vis to NIR photoconduction in cyclopalladated complexes.

The incorporation of a rigid core, formed by a cyclopalladated azobenzene fragment bonded to an ancillary Schiff base ligand, into molecules with 12 or 11 peripheral alkyl chains has been successfully achieved. These new complexes, 1 and 2, respectively, are columnar liquid crystals between room temperature and about 50 degrees C. Both cyclometallated and ancillary ligands have been polyalkylated through either aryl ester (electron-withdrawing group) or aryl ether (electron-releasing group) linkages, in order to tune the HOMO/LUMO energy levels.