Synthesis of Novel Discotic C_(60)-triphenylene Derivative by 1,3-Dipolar Cycloaddition

1 Introduction Fullerene has received considerable attention and a great researching interest due to its unique structure and interesting properties[1―3]. Many functional groups have been introduced, often region- or stereo-selectively, for tuning the physical properties of C60and for constructing supramoleculararchitectures^[4-6].

Phase behaviors of binary mixtures composed of electron-rich and electron-poor triphenylene discotic liquid crystals

Disk-like liquid crystals（DLCs） can self-assemble to ordered columnar mesophases and are intriguing onedimensional organic semiconductors with high charge carrier mobility.To improve their applicable property of mesomorphic temperature ranges,we exploit the binary mixtures of electronic donor-acceptor DLC materials.The electron-rich2,3,6,7,10,11-hexakis（alkoxy）triphenylenes（C4,C6,C8,C10,C12） and an electron-deficient tetrapentyl triphenylene-2,3,6,10-tetracarboxylate have been prepared and their binary mixtures have been investigated.The mesomorphism of the1：1（molar ratio） mixtures has been characterized by polarizing optical microscopy（POM）,differential scanning calorimetry（DSC）,and small angel x-ray scattering（SAXS）.The self-assembled monolayer structure of a discogen on a solid-liquid interface has been imaged by the high resolution scanning tunneling microscopy（STM）.The match of peripheral chain length has important influence on the mesomorphism of the binary mixtures.

Triphenylene adsorption on Cu(111) and relevant graphene self-assembly

Investigations on adsorption behavior of triphenylene(TP)and subsequent graphene self-assembly on Cu(111)were carried out mainly by using scanning tunneling microscopy(STM).At monolayer coverage,TP molecules formed a long-range ordered adsorption structure on Cu(111)with an uniform orientation.Graphene self-assembly on the Cu(111)substrate with TP molecules as precursor was achieved by annealing the sample,and a large-scale graphene overlayer was successfully captured after the sample annealing up to 1000 K.Three different Moirépatterns generated from relative rotational disorders between the graphene overlayer and the Cu(111)substrate were observed,one with 4°rotation between the graphene overlayer and the Cu(111)substrate with a periodicity of 2.93 nm,another with 7°rotation and 2.15 nm of the size of the Moirésupercell,and the third with 10°rotation with a periodicity of 1.35 nm.

PHASE STRUCTURES AND TRANSITION BEHAVIORS OF A TRIPHENYLENE DISCOTIC LIQUID CRYSTAL

The phase behaviors and structures of a triphenylene-derived discotic liquid crystal （LC） hexa-n-octoxyl- triphenylene （C8HET） were studied using the combined techniques of differential scanning calorimetry （DSC）, wide angle X-ray diffraction （WAXD）, selected area electron diffraction （SAED） and polarized light microscopy （PLM）. Onedimensional （1D） powder WAXD results at different temperatures coupled with DSC and PLM observations revealed that the C8HET compound possessed an LC phase and three different crystalline （K3, K2 and K1） phases below the isotropic （I） melt. The I←→ LC phase transition was thermodynamically reversible and independent of the heating and cooling rates. The development and experimental observation of the three crystalline phases relied on different thermal histories. Among the three crystalline phases in CSHET, the K3 phase is the most stable phase, while the K2 and K1 phases are metastable. Note that the K1 phase only formed via a quenching process. Oh the basis of structure sensitive diffraction experiments such as 2D WAXD of oriented samples and SAED of single crystals, detailed structures and molecular packings of these four ordered phases were identified. The LC phase exhibited a hexagonal columnar phase with 2D lattice dimensions ofa = b = 2.38 nm and γ= 120°. All the three crystalline phases possess monoclinic unit cells, yet the y angle is not 90° in the cases of the K2 and the K3 phases, while in the case of the K1 phase the a angle is not 90°.

Theoretical study on the charge transport properties of triphenylene discogens with a phenylpropionyloxy or 3-phenylpropenoyloxy side chain

Charge transport is one of the most important properties in organic materials.Charge transport properties of triphenylene discogens with a phenylpropionyloxy or 3-phenylpropenoyloxy side chain have been investigated computationally on the basis of semi-classical Marcus theory.The results show that three triphenylene derivatives have high charge mobility.Title compounds have much better electronic mobility than the triphenylene.The triphenylenes containing 3-phenylpropenoyloxy have better hole mobility,but smaller electronic mobility than the triphenylenes with phenylpropionyloxy.For the triphenylene discogens with a phenylpropionyloxy,the longer the alkloxy chains,the better the positive charge transfer rate,but the smaller the negative charge transfer rate.

Synthesis and mesomorphism of diacetylene-bridged triphenylene discotic liquid crystal dimers

Connecting two discotic mesogens via a spacer not only stabilizes the columnar mesophase but also leads to the formation of glass columnar phase, and therefore improves the physical properties of discotic liquid crystals as organic semiconductor. Here, we report the synthesis of eight diacetylene-bridged triphenylene discotic liquid crystal dimers, [C18H6(OCnH2n+1)4(OMe)O2C-C8H16-C≡≡ C-]2, 3(n), (n = 4-8), [C18H6(OC6H13)5O2C-C8H16-C≡≡ C-]2, 6 and [C18H6(OC6H13)5O-(CH2)m-C≡≡ C-]2, 8(m), (m = 1, 3) by Eglinton coupling reaction. The thermotropic liquid crystal properties were studied by differential scanning calorimetry and polarized optical microscopy. The results are showed as follows: the length of peripheral alkyl chains of triphenylene influenced properties of liquid crystal dimers; dimers 3(n) (n = 5-8) and 6 had glass columnar phase, and no crystallization was observed above -50℃ for all the triphenylene dimers; compared with 3(6), 6 showed higher molecular symmetry, more stable columnar mesophase and wider mesophase range. The connecting group, length and rigidity of spacer had important influence on the mesomorphism of diacetylene-bridged triphenylene discotic liquid crystal dimers.

Synthesis of Mixed Tail Triphenylene Discotic Liquid Crystals： Molecular Symmetry and Oxygen-Atom Effect on the Stabilization of Columnar Mesophases

Small change in chemical structure of discotic liquid crystals can cause big difference in their mesomorphism. Replacing of the alkoxy peripheral chains of triphenylene by oxygen-atom containing ester chains would result in novel mesomorphism. A series of mixed tail triphenylenes containing propoxyacetyloxy and alkoxy, abbreviated as C18H6（OCnH2n＋1）3（OCOCH2OC3H7）3, n=4-8, and hexa（propyloxyacetyloxy）triphenylene, C18H6（OCOCH2OC3H7）6 were synthesized. Thermal gravimetry analysis （TGA） of three discogens showed that they had good thermal stability till 350 ℃. The mesomorphism was investigated through differential scanning calorimetry （DSC） and polarized optical microscopy （POM）. The preliminary X-ray diffraction （XRD） results of one compound showed that it exhibited ordered hexagonal columnar （Colho） mesophase. These mixed tail triphenylene derivatives possessed much stable Colho mesophase and wider mesophase ranges than their hexaalkoxytriphenylene C18H6（OR）6 and hexaalkanoyloxytriphenylene C18H6（OCOR＇）6 analogues. The asymmetrical compounds 2,6,11-trialkoxy-3,7,10-tri（2-propyloxyacetyloxy）triphenylenes with n=5-8 displayed higher clearing points and wider temperature ranges than their symmetrical isomers 2,6,10-trialkoxy-3,7,11-tri（2-propyloxyacetyloxy）- triphenylenes, while C18H6（OCOCH2OC3H7）6 had the highest clearing point due to the β-oxygen-atom effect.

Synthesis of unsymmetric triphenylene discotic liquid crystals with a semi-fluorinated chain and the influence of fluorophobic effect on mesogenic behavior

The fluorophobic effect of the semi-fluorinated chain of discotic molecules efficiently improves the stability of columnar mesophase.Low symmetric discogens exhibit decreased melting points and wide mesophase ranges.A series of triphenylene derivatives 1,C18H6(OCnH2n+1)4(OMe)(O2CC2H4C6F13),and their hydrocarbon analogues 2,C18H6(OCnH2n+1)4(OMe)(O2CC8H17),n = 4―8,were synthesized for the investigation of the influence of semi-fluorinated peripheral chain and molecular symmetry on mesomorphism.The structures were characterized with 1H NMR and MS.The mesomorphism was studied with differential scanning calorimetry(DSC) and polarizing optical microscopy(POM).The results showed that all triphenylene derivatives exhibited enantiotropic columnar mesophase.The semifluorinated triphenylenes 1a―1e displayed higher melting points and clearing points than their hydrocarbon analogies 2a―2e.Most of them were in columnar mesophase at room temperature.

Synthesis and Liquid Crystalline Behavior of Side Chain Liquid Crystalline Polymers Containing Triphenylene Discotic Mesogens with Different Length Flexible Spacers

A series of side chain liquid crystalline polymers （SCLCPs） containing triphenylene （Tp） units in the side chains, denoted as PMTS （without spacer） and PMTnS （n = 2, 3, 4, 6, which is the number of the methylene units between the main chain and Tp moieties in the side chains）, with different lengths of spacers were synthesized through conventional free radical polymerization. The chemical structures of the monomers were confirmed by 1H/IaC-NMR, and the phase behaviors were examined by differential scanning calorimetry （DSC）, polarized optical microscopy （POM） and wide-angle X-ray diffraction （1D and 2D WAXD）. The molecular characterization of the polymers was performed with 1H-NMR, gel permeation chromatography （GPC） and thermogravimetric analysis （TGA）. The phase behaviors of the polymers have been investigated by a combination of techniques including DSC, POM, 1D and 2D WAXD. The results showed that the length of spacer has significant effects on the LC phase behavior of polymers. For PMTS and PMT2S, they displayed the columnar phase developed by the Tp moieties and the main chain as a whole due to the strong coupling effect of the Tp moieties and the main chain. For the PMT3S, PMT4S and PMT6S, they formed the symmetry hexagonal columnar （~n） phase owing to the decoupling effect. All of these indicated that the ＂decoupling effect＂ or ＂coupling effect＂ depended on the length of spacers, leading to the different LC phase formation mechanism.

Disk-shaped Symmetric Hexa-substituted Triphenylene Derivatives： Synthesis, Physical Properties and Self-assembly

A series of triphenylene derivatives with six symmetric substituents was synthesized from hexabromotriphenylene. The synthesis was conducted by six-fold palladium-catalyzed Hagihara-Sonogashira crosscoupling reactions to yield the hexa-alkynyl substituted triphenylene derivatives of HTPI, HTP2, HTP3 and HTP4. The six symmetric substituents can not only endow the triphenylene the longer π-conjugated range, but also increase the solubility of the compounds. Their photophysical, electrochemical, thermal properties were investigated respectively. With the comparison of their properties, the structure-property relationships were established which demonstrated the influences of different substituents on the electronic nature and the mesomorphic phase of these disk-shaped molecules. In addition, with the scanning electron microscopy（SEM） and polarized optical microscopy（POM） characterization, the self-assembly behaviors of the compounds were also investigated.

Synthesis of disk-rod-disk liquid crystal trimers by using click chemistry

A series of disk-rod-disk liquid crystal trimers were synthesized.CuI-NEt3 catalyzed alkyne azide cycloaddition in toluene at room temperature connected two triphenylene discogens to a biphenyl rod-shaped mesogen.The trimers were characterized by using 1H NMR,IR,and high resolution mass spectrometry.The mesomorphic properties were investigated using polarized optical microscopy(POM) ,differential scanning calorimetry(DSC) ,and wide-angle X-ray diffraction.The results showed that the trimers exhibited rectangular columnar mesophase(Colr) .The length of the flexible spacer connecting the three segments has prominent influence on the phase transition temperatures of the trimers.