Triphenylene Mesogens Research Articles

Dynamic change of molecular conformation generating a variation of liquid crystalline phases for triphenylene mesogens with peripheral alkoxyazobenzenes

ABSTRACT A triphenylene mesogen which possesses six dodecyloxyazobenzene units at the periphery linked by propylene-ether chain (2-C12-3) was synthesised and its mesomorphic phase transition behaviour was investigated. It was found that 2-C12-3 exhibits six mesophases including one monotropic phase. The calamitic-discotic bi-mesomorphic phase transition was also observed. As cooling the compound at the temperature of iso phase, SmA phase comes up and further cooling gives Col ob phase. In comparison to the corresponding ester-linked derivative (1-C12-3), which shows only two mesophases (SmA and Colr), the linkage part connecting triphenylene unit and the peripheral alkoxyazobenzenes significantly affect the molecular ordering in mesophase, though the bi-mesomorphic property is maintained in the case of dedecyloxy chains.

Synthesis, self-assembly and optical properties of some rigid π-bridged triphenylene dimers

π-Conjugated liquid-crystalline dimers consisting of two triphenylene mesogens connected through a rigid molecular bridge have been synthesized. Mesophases, gels and optical properties have been investigated as a function of the bridge nature.

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

ABSTRACTWe 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.

Design of Janus triphenylene mesogens: Facile synthesis, mesomorphism, photoluminescence, and semiconductivity

A new variety of non-symmetrical triphenylene-based discogens has been synthesized by intramolecular Scholl cyclodehydrogenation reaction of kinked terphenylenes using the FeCl3/MeNO2 couple as an efficient oxidant. The “Janus-like” tetrakis(alkoxy)triphenylene discogens containing electron-withdrawing groups, such as cyano-, chloro- and fluoro-substituents, or electron-donating moieties, such as carbazole, thiophene and naphthalene at the opposite of the alkylated side were prepared in good to high yields. Polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) investigations revealed that six of the 14 discogens synthesized exhibit a hexagonal columnar mesophase. These chromophores emit bright blue light from 350 nm to 500 nm in solution depending on the extension of their π-conjugation. In addition, all six columnar liquid crystals show non-dispersive time-of-flight photocurrent transportation, with charge carrier drift mobility in the range of 10−3 to 10−4 cm2 V−1 s−1, higher or in the same range as their symmetrical hexa(alkoxy)triphenylene parent compounds.

2B05 長鎖末端にカルボン酸を有するトリフェニレン液晶における水素結合相互作用の変化と相転移挙動(化学・材料)

2B05 長鎖末端にカルボン酸を有するトリフェニレン液晶における水素結合相互作用の変化と相転移挙動(化学・材料)

Influence of main chain on the phase behaviors of side‐chain liquid‐crystalline polymers with triphenylene mesogens of long alkyl tail substituents

ABSTRACTA series of side‐chain liquid‐crystalline polymers (SCLCPs) containing triphenylene mesogen, in which the long alkyl tail Tp connected directly with main chain, were synthesized successfully. The chemical structures of the monomers were confirmed by 1H NMR and mass spectrometry. The phase behaviors of polymers were investigated by a combination of techniques, including DSC, POM, 1D/2D WAXD, and SAXS. The experimental results suggested that the type of main chain played an important role in the LC phase structures of these polymers. Because of the steric effects of side chains and the coupling effects between the Tp moieties and the main chains, all the polymers exhibited columnar phase. However, the SCLCPs with poly(vinyl benzene methyl ether) or polynorbornene backbone displayed hexagonal columnar phase, while those with polyacrylate or polymethacrylate backbone presented columnar nematic phase, and the one with poly(vinyl benzoate) main chain showed rectangular columnar phase. Moreover, the clearing temperatures (Ti) changed with change in main chain. Especially, the Ti of the SCLCP with polymethacrylate backbone was above 300 °C. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 754–766

Highly Segregated Lamello-Columnar Mesophase Organizations and Fast Charge Carrier Mobility in New Discotic Donor-Acceptor Triads.

Four new donor-acceptor triads (D-A-D) based on discotic and arylene mesogens have been synthesized by using Sonogashira coupling and cyclization reactions. This family of triads consists of two side-on pending triphenylene mesogens, acting as the electron-donating groups (D), laterally connected through short lipophilic spacers to a central perylenediimide (PI), benzo[ghi]perylenediimide (BI), or coronenediimide (CI) molecular unit, respectively, playing the role of the electron acceptor (A). All D-A-D triads self-organize to form a lamello-columnar oblique mesophase, with a highly segregated donor-acceptor (D-A) heterojunction organization, consequent to efficient molecular self-sorting. The structure consists in the regular alternation of two disrupted rows of triphenylene columns and a continuous row of diimine species. High-resolution STM images demonstrate that PI-TP2 forms stable 2D self-assembly nanostructures with some various degrees of regularity, whereas the other triads do not self-organize into ordered architectures. The electron-transport mobility of CI-TP2, measured by time-of-flight at 200 °C in the mesophase, is one order of magnitude higher than the hole mobility. By means of this specific molecular designing idea, we realized and demonstrated for the first time the so-called p-n heterojunction at the molecular level in which the electron-rich triphenylene columns act as the hole transient pathways, and the coronenediimide stacks form the electron-transport channels.

Drastic Change of Mesomorphism Induced by the Fluorination of Peripherally Attached Phenyl Groups in Triphenylene Mesogens

Triphenylene mesogens possessing fluorinated phenyl groups connected to the central triphenylene core with ester and ether linkages were compared on the mesomorphism. The results indicate that the fluorination of the peripheral phenyl groups arises strong intermolecular interactions among the peripheral parts to make the molecules stack easily to form a columnar structure. The thermal stability of the columnar mesophases is modified by the replacement of linkage group and the clearing temperature of Colh mesophase for the ester derivative is higher than that of the ether one. The carrier mobility evaluated by Time-Of-Flight (TOF) technique is shown to be in the order of 10−3 cm2 V−1 s−1 and 10−2 cm2 V−1 s−1 for the ester and ether derivatives, respectively.

Carrier Mobility Behavior of Triphenylene Mesogen with a Hydrogen Bonding Amide Group

The charged carrier mobility was measured for the Colh mesophase of a hexa-substituted triphenylene of which one of the peripheral pentyloxy chains is replaced with n-butylamideethyleneoxy group (1) to compare that of hexapentyloxytriphenylene (2). The positive charge mobility was observed to be in the order of 10−5 ∼ 10−4 cm2 V−1 s−1. Though the thermal stability of Colh mesophase is higher than that of 2, the carrier mobility of 1 is smaller by one order of magnitude probably due to the presence of an electrical dipole of the carbonyl group. Also the temperature dependence of mobility in 1 exhabits a thermally activation behavior in a stronger way than in 2, indicating the hydrogen bond interaction affect the thermal behavior of charge hopping by a modification of molecular dynamics.

Columnar liquid crystalline assembly of doubly discotic supermolecules based on tetra-triphenylene-substituted phthalocyanine

A series of doubly discotic supermolecules with four triphenylene (Tp) mesogens attached to a phthalocyanine (Pc) core via flexible alkyl spacers were designed and synthesized. The samples were denoted as Pc(Tp)4. Two alkyl chain lengths (C5 and C12) in the Tp arms and two spacer lengths (C6 and C10) were used to study columnar liquid crystalline (LC) self-assemblies in Pc(Tp)4 samples. The mesophase morphology was studied by polarized light microscopy and X-ray diffraction techniques. When the spacer length was relatively long (C10), a normal hexagonal columnar structure with the unit cell dimension close to those for the parent Tp or Pc liquid crystals was observed. The Pc columns packed either randomly or in a hexagonal superlattice in the Tp matrix. When the spacer length was short (C6), the Tp arms and the Pc core were tightly coupled together, and thus the whole supermolecules stacked together to form a super-LC column. A column-in-column rectangular mesophase with unit cell dimensions close to the size of the entire supermolecule was observed.

The Synthesis and Phase Behavior of a Novel Discoticnematic Triphenylene Mesogen and its Application to an Optically Anisotropic Film

A novel discotic triphenylene derivative bearing one triphenylene discogen as core and three cyano-biphenyl moieties was synthesized and its thermal behavior was studied using polarizing optical microscope, differential scanning calorimeter and X-ray diffraction. It was found that this molecule containing [decylene] spacers showed nematic phase. After being mixed with methyl methacrylate (MMA), the discogen showed nematic phase at the mesophase temperature range (64~85 °C) and oriented spontaneously in the mixture after annealing for 2 hours in the mixture. The orientation can be stabilized by the polymerization of MMA. The orientation can be fixed by the polymerization of MMA. It was treated directly on glass substrate, which surface did not treat by polyimide film and confirmed the orientation was proved by X-ray diffraction. This offers If the alignment of the discotic molecules can be freely controlled and fixed, a useful mean to produce new area of optically anisotropic film will be produced with this material.

Drastic enhancement of discotic mesomorphism induced by fluorination of the peripheral phenyl groups in triphenylene mesogens

Four derivatives of hexakis(4-alkoxybenzoyloxy)triphenylene, for which peripheral phenylene groups are fluorinated at the inner and the outer positions were studied for their mesomorphic behaviour to reveal that the alteration of fluorinated positions in the phenyl rings leads to a drastic change of the mesomorphism involving the thermal stability.

Disc‐Shaped Triphenylenes in a Smectic Organisation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Infrared Spectral Studies of Triphenylene Mesogens Possessing Terminal Functional Groups in the Peripheral Chains for Hydrogen-Bond Interaction

Temperature dependence of infrared spectra for three homologues of the triphenylene mesogens with two terminal carboxylic acids was measured. These mesogens show Colh mesophase. These results revealed the existence of some hydrogen bonding interactions in the isotropic, mesomorphic as well as solid phases. The increase of the dimeric C = O (ca. 1712 cm−1) and the decrease of the monomeric C = O (ca. 1740 cm−1) were observed at the isotropic to Colh phase transition on cooling. The absorption intensity of the dimeric C = O stretching band in Colh phase is larger than that in the isotoropic phase. It was indicated that for the explanation of Colh thermal stability for these homologues molecular rotational fluctuation around the columnar axis in Colh is significantly suppressed by the hydrogen bonding interaction and the suppression depends on the spacer length in their homologues, considering that the thermal stability of Colh phase is related to both the rotational fluctuation and the instability of hexagonal packing of molecules and these could be operated by hydrogen bond interaction.

Disc-shaped triphenylenes in a smectic organisation

A layered phase (SmA) was observed in a novel linked disc-rod mesogen, containing a triphenylene mesogen and attached to three cyanobiphenyl moieties.

2B02 Rod-disc形状変化を伴う相転移現象を示す新しいタイプのトリフェニレン液晶(化学・材料)

2B02 Rod-disc形状変化を伴う相転移現象を示す新しいタイプのトリフェニレン液晶(化学・材料)

Infrared studies on hydrogen bond interaction in a homologues series of triphenylene discotic liquid crystals having carboxylic acids at the peripheral chains

Temperature dependence of infrared spectra was measured in a hexagonal columnar (Col h) mesophase for three homologues of a triphenylene mesogen with two terminal carboxylic acids. It was found for all homologues that the band intensity of hydrogen bonded C=O (approx. 1710 cm −1), as a carboxylic acid dimer, increases at the isotropic to Col h phase transition on cooling, while the monomeric C=O (approx. 1740 cm −1) band decreases. The results strongly indicate that the rotational and translational fluctuations in Col h mesophase is significantly suppressed by the hydrogen bonding interaction and the suppression depends on the spacer length connecting the triphenylene core and carboxylic acid group leading to the modification of mesomorphic thermal stability.

Fluorination Effect of the Peripheral Chains on the Mesomorphic Properties in Discotic Liquid Crystals of Hexasubstituted Triphenylene

Abstract Two homologues of novel triphenylene mesogens possessing –O(CH2)3CF3 (F1) and –O(CH2)3(CF2)5CF3 (F6) were synthesized and investigated on the mesomorphic behavior to reveal that these show a hexagonal columnar (Colh) mesophase. The mesomorphic behavior is obviously different from those of the corresponding hydrocarbon homologues, –O(CH2)3CH3 (C1) and –O(CH2)8CH3 (C6). Interestingly, it was found that F1 shows a disordered Colh phase, though C1 forms only a plastic hexagonal columnar (Colhp) mesophase.

Calamitic and discotic mesophases formed by kinetically controlled rod–disc alternation of molecular shape in a triphenylene–azobenzene mesogenic system

A triphenylene mesogen with the peripheral azobenzene units was found to show kinetically controlled bimesomorphism, with a metastable smectic and a stable hexagonal columnar (Colh) phases on cooling, which is caused by the rod–disc alternation of the molecular shape.

An Infrared Technique for Alignment Control of Discotic Liquid Crystals: A Possible Fabrication Technology for Organic Micro/Nano Electronic Devices

An infrared technique for molecular alignment control of discotic columnar liquid crystals is described. The liquid crystal domain change was induced in hexagonal columnar mesophase by infrared irradiation with a vibrational excitation of the chemical bonds in the triphenylene mesogen. In the new domain a uniform alignment of molecules was attained and the behaviour is essentially related to the polarisation of the incident beam. Also the new domain is quite stable, though depending on temperature. However, such a new domain formation was not observed in the discotic nematic phase.