Hailiang Ni

Truxene discotic liquid crystals with two different ring substituents: synthesis, mesomorphism and high charged carrier mobility

Discotic liquid crystals as a kind of promising organic electronic materials show self-assembly property as well as high charged carrier mobility. New truxene discogens, six 3,8,13-tri(alkoxy)-2,7,12-tri(methoxy)truxenes and two 3,8,13-tri(alkoxy)-2,7,12-tri(hydroxy)truxenes, have been synthesised with improved yields, were fully characterised and exhibited good thermal stability. The mesomorphism has been investigated by using polarised optical microscopy, differential scanning calorimetry and X-ray diffraction, and they exhibited ordered hexagonal columnar mesophase. More importantly, the charge carrier mobilities of 6d and 7f have been measured by using time-of-flight technique and 7f displayed hole drift mobility rate of 4.2 × 10−2 cm2 V−1 s−1 in the Colho phase and 0.1 cm2 V−1 s−1 at a lower temperature M mesophase.

The influence of alkyl chain substitution pattern on the two- and three-dimensional self-assembly of truxenone discogens

The synthesis of new discotic liquid crystals and the study of self-assembly behaviours are important for the supramolecular chemistry and organic electronics. Six new truxenone discogens 7a–f with different alkyl chain substitution patterns were synthesised and all exhibited only one three-dimensional ordered hexagonal columnar mesophase with wide temperature ranges including room temperature, which were characterised with polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. The self-assembly behaviours in solutions were studied by using concentration-variation 1H NMR and scanning electron microscopy. The two-dimensional ordered self-assembly of 7c and 7f on the liquid–solid interface of highly oriented pyrolytical graphite were imaged by scanning tunnelling microscopy, and the results showed that the two-dimensional monolayer self-assembled structures on the atomically flat surfaces can be controlled by the peripheral alkyl chain substitution patterns.

New phosphorescent platinum(II) complexes: lamellar mesophase and mechanochromism

Several new square planar platinum(II) complexes based on modified 2-phenylpyridine derivatives as the main ligand and picolinic acid as the auxiliary ligand were synthesized and their photophysical properties, and mechanochromic and liquid crystalline behavior were investigated. It is found that only the Pt–L1 complexes, in which one flexible long chain is attached to each end of 2-phenylpyridine, display monotropic smectic liquid crystalline behavior. Moreover, mechanochromism has been observed by grinding the solid complexes. It seems that the liquid crystalline and mechanochromic properties of these complexes are relative to the number of flexible alkoxy chains in the cyclometalated ligand.

Synthesis and characterisation of 3-armed dendritic molecules with triphenylbenzene or triphenyltriazine as core and triphenylene derivative as shells

Two series 3-armed dendritic molecules with their 1,3,5-tris(4-methyloxyphenyl) benzene or 2,4,6-tris(4- hydroxylphenyl)-1,3,5-s-triazine core and triphenylene derivative shells connected by soft hydrocarbon chains have been synthesised and fully characterised. Whether liquid crystal (LC) or photoluminescence materials have been tuned by changing the length of the soft chain and they have been studied by POM, DSC, XRD, UV-Vis and PL. The results show that all the new dendritic compounds display UV to blue fluorescence in solvents such as DCM, THF and acetone. The TC3 compound bearing 1,3,5-tris(4-hydroxylphenyl) benzene core exhibits LC property with rectangular columnar phase (Colr) on cooling.

Novel columnar metallomesogens based on cationic platinum(II) complexes without long peripheral chains

Phosphorescent cationic platinum(II) complexes were obtained and among them the complexes without any peripheral flexible chains around the platinum(II) center show thermotropic columnar liquid crystal properties.

Monosubstituted ferrocene liquid crystals containing click triazole with a wide nematic phase temperature range

ABSTRACT New monosubstituted ferrocenomesogens of the 1,4-substituted-1,2,3-triazole series 3a-3d and the 5-halogen-1,4-substituted-1,2,3-triazole series 4a-4d were successfully synthesised through a facile and versatile synthetic route using click reactions with moderate yields, in different atmospheres, and catalysed by different amounts of CuX (X = Br, I). Two series of compounds exhibited a typical nematic liquid crystal texture, and the 5-halogen-1,4-substituted-1,2,3-triazole series 4 had a wider mesomorphic temperature range than the corresponding series 3 due to the effect of the halogen atom substituent on the triazole. These compounds showed similar absorption spectra, but the fluorescence emission spectra of 4 were obviously redshift relative to 3. Cyclic voltammetry investigations revealed that the redox-active ferrocenyl groups of 3 and 4 follow one-electron transfer processes. GRAPHICAL ABSTRACT

Synthesis and characterization of new H-shaped triphenylene discotic room-temperature liquid crystal tetramers by a copper-free click reaction

Herein, four new H-shaped triphenylene discotic liquid crystal tetramers have been designed and synthesized using a copper-free [3+2] cycloaddition reaction between the triphenylene dimer and diazide compounds. To probe the molecular self-assembly and mesophase properties, the length and rigid spacers in diazide have been tailored. The tetramers 7 with a soft spacer display a room-temperature enantiotropic DLC mesophase, and X-ray diffraction confirms that they exhibit an unusual mesophase of a lamellar–hexagonal columnar phase (Colhl). The results of the photophysical tests show that all the new H-shaped DLC tetramers display relatively high intensity photoluminescence properties.

Ortho-platinated metallomesogens based on rod mesogenic unit of 2-phenylpyridine derivatives: synthesis, high linearly polarised and phase-state-dependent luminescence

ABSTRACT Three series of cyclometalated platinum (II) complexes [(cbCnppyC16) Pt(acac) (an), (cbCnppyC16)Pt(pic) (bn) and (cbCnppyC16)Pt(picd) (cn)] were obtained, where cbCnppyC16 (2-(4-hexadecyloxyphenyl)-5-[(1,1ʹ-biphenyl)-4-carbonitrile-4ʹ-alkoxy-methoxyl]pyridine) is as cyclometalated ligand, and Hacac (acetylacetone), Hpic (picolinic acid) and Hpicd (5-[(1,1ʹ-biphenyl)-4-carbonitrile-4ʹ-dodecyloxy]oxy-2-car boxylpyridine) are auxiliary, respectively. The liquid crystalline behaviour, polarised emission, photophysical and phase-state-dependent luminescence properties for all platinum (II) complexes were investigated systematically. Cyclometalated platinum (II) complexes bn show smectic phase structure; however, an and cn show nematic phase. The platinum (II) complexes exhibit different photoluminescence (PL) behaviour in solution, crystal phase, liquid crystal phase and amorphous thin films. Moreover, these metallomesogens show strongly polarised photouminescence in liquid crystalline phases. Especially, the PL dichroic ratio is up to 24.6 in nenatic phase. Graphical Abstract

Carrier transport property of truxene discotic liquid crystals with three different ring substituents

In this study, the charge carrier transport property of 3,8,13-trioctyloxytruxene [Trx(OC8)3] and its analogues, to which two different ring substituents of hydroxyl [Trx(OH)3(OC8)3] and methoxy [Trx(OMe)3(OC8)3] groups are introduced, has been studied relative to mesomorphism. Three analogues exhibit a hexagonal columnar (Colh) mesophase and their thermal stability increases with the introduction of hydroxyl and methoxy groups. The drift mobility measurements of Trx(OC8)3 and Trx(OH)3(OC8)3 reveal that the drift mobility is on the order of 5 × 10−2 cm2 V−1 s−1 in the Colh phase and it increases to 10−1 cm2 V−1 s−1 at the Colh-metastable phase transition, although Trx(OMe)3(OC8)3 shows a drift mobility of 1 × 10−2 cm2 V−1 s−1 in the Colh phase with temperature dependence. These results indicate that truxene with three alkoxy chains is an interesting molecular core for mesophase semiconductors.