Structural factors controlling the transition between columnar hexagonal and helical mesophase in triphenylene liquid crystals.

A series of novel triphenylenes has been synthesised by a combination of palladium catalysed coupling, oxidative cyclisation, bromination and nucleophilic aromatic substitution. The new derivatives are designed to have structures which are intermediate between the known symmetrical materials hexakis(hexyloxy)triphenylene and hexakis(hexylthio)triphenylene. The compounds having four hexyloxy and two hexylthio substituents form only Colh mesophases. Triphenylenes having four hexylthio and two hexyloxy substituents also give Colh mesophases but 3,6-bis(hexyloxy)-2,7,10,11-tetrakis(hexylthio)triphenylene 5 is unique in that it cools into a stable, more ordered phase. The low temperature phase, which appears to be indefinitely stable at ambient temperature, is assumed to be helical based on transition enthalpy data

First examples of functionalisation of meso-aryl tetrabenzotriazaporphyrins (TBTAPs) through cross-coupling reactions

Recent synthetic advances have given convenient access to tetrabenzotriazaporphyrins (TBTAPs) functionalised with meso-aryl substituents. In this paper we report the first examples of further functionalization of the meso-sites through Suzuki-Miyaura and copper-free Sonagashira cross-coupling reactions of the meso-(bromophenyl)TBTAPs, demonstrating the breadth of new materials design now possible in the hybrid macrocycles

Dendroid Peptide Structural Mimetics of Omega-Conotoxin MVIIA based on a 2(1H)-Quinolinone Core

Three mimetics of the peptide -Conotoxin MVIIA have been synthesised following the dendroid approach. The three key central amino acids of the natural peptide are mimicked by phenylguanidine (arginine), isopentyl (leucine) and aryl alcohol (tyrosine) attached to a quinolinone core at the 1- and 8-positions. The derivatives are designed to position these key groups in similar spatial orientation to that of the natural peptide in a structure that will have limited conformational flexibility. Key steps of the syntheses involve selective N-alkylation of quinolinone derivatives and guanylation of aryl amines

A modified route to unsymmetrically substituted triphenylenes, new functionalised derivatives and twins, and the smallest reported triphenylene mesogen

We report the unexpected observation of columnar mesophase formation in a simple 2,7-dibromotetramethoxytriphenylene – by far the most lightly substituted discotic mesogen in this class. This derivative was prepared alongside the 3,6-dibromotriphenylene isomer to demonstrate an alternative, modified synthetic strategy that permits late-stage interchange of alkyl chain substituents. The new method is employed alongside the original route to deliver several new materials, including a conjugated ferrocene-triphenylene-ferrocene triad, a BODIPY-triphenylene-BODIPY triad and a new nematic twin linked through imine bridges

Synthesis and crystal structure of 1,3-bis[(3,4-dicyano)phenoxy]-4,6-dinitro-benzene, C22H8N6O6

C22H8N6O6, monoclinic, P21/n (no. 14), a = 15.3939(6) Å, b = 7.3053(3) Å, c = 16.8282(6) Å, β = 91.567(3)°, V = 1891.74(13) Å3, Z = 4, Rgt(F) = 0.0510, wRref(F2) = 0.0867, T = 140(2) K

Synthesis and Mesophase Properties of Triphenylene Dimers Linked through Linear and Bent Alkyne‐Aryl‐Alkyne Bridges

Nematic mesophase formation in disc-like systems remains relatively rare compared to higher-order columnar organisation, but it is observed in some rigid dimeric systems. Mesophase formation in rigid discotic dimers has been sequentially probed and is shown to be predictably controlled through structural choice of the bridge. Moderately bent bridges shorten the discogen separation and reduce conformational freedom. Severely bent dimers (1,2-phenylene bridge) show no mesophases but, as the angle is widened, columnar and nematic organisation becomes possible and progressively more favoured. The linear arrangement gives the most stable columnar mesophase and a narrow-range nematic mesophase

Electron charge transport in non-peripherally substituted copper phthalocyanine

Bottom-gate, bottom-contact organic thin film transistors (OTFTs) were fabricated using solvent soluble copper-1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyanine as the active semiconductor layer. The compound was deposited as 70 nm thick spin-coated films onto gold source-drain electrodes supported on octadecyltrichlorosilane treated 250 nm thick SiO2 gate insulator. The analysis of experimental results showed the n-type field effect behaviour. Devices annealed at 100 oC under vacuum were found to exhibit the field-effect mobility of 0.0989 cm2 V-1 s-1, with an on/off current modulation ratio of ∼106, a reduced threshold voltage of 0.7 V and a sub-threshold swing of 2.12 V decade-1. The variations in surface morphology of the devices are found reflected considerably in the electrical measurements. The device contact resistance was found to be decreased as the gate bias increased and also with the annealing

Hybrid phthalocyanine/lead sulphide nanocomposite for bistable memory switches

Asimple, one-step method is employed to produce, at room temperature, a single layer of an organicinorganic nanocomposite containing non-aggregated lead sulphide (PbS) quantum dots (QDs) embedded in a 130 nmthick solution processed film of the organic semiconductor 6PcH2 (metal-free, non-peripherally substituted octahexyl phthalocyanine) on indium tin oxide. The mean size of PbS QDs is found from x-ray diffraction and transmission electron microscopy techniques to be much smaller than the Bohr radius. Further evidence of the quantum confinement effect is provided by a blue shift in the absorption spectrum and the increased band gap of 1.95 eV with respect to bulk PbS. The current–voltage characteristics of the hybrid and pristine 6PcH2 films, both in a sandwich configuration with the aluminium top electrode, exhibit bistable switching type hysteresis. The on-off ratio of the nanocomposite device is at least three orders of magnitude higher than that for 6PcH2 organic films, while both devices operate at a very low bias voltage of 0.5 V. The inclusion of the PbS QDs into the 6PcH2 film enhances the conductivity by nearly two orders of magnitude over that of a comparable pristine 6PcH2 film due to the formation of a charge transfer complex with PbS QDs and 6PcH2 acting as acceptors and donors of electrons, respectively

A π-Extended Donor-Acceptor-Donor Triphenylene Twin linked via a Pyrazine-bridge

Beta-amino triphenylenes can be accessed via palladium catalyzed amination of the corresponding triflate using benzophe-none imine. Transformation of amine 6 to benzoyl amide 18 is also straightforward and its wide mesophase range demon-strates that the new linkage supports columnar liquid crystal formation. Amine 6 also undergoes clean aerobic oxidation to give a new twinned structure linked through an electron-poor pyrazine ring. The new discotic liquid crystal motif contains donor and acceptor fragments, and is more oval in shape rather than disk-like. It forms a wide range columnar mesophase. Absorption spectra are strong and broad; emission is also broad and occurs with a Stokes shift of ca. 0.7 eV, indicative of charge-transfer characte