Triphenylene Moieties Research Articles

First examples of room-temperature discotic nematic liquid crystals exhibiting ambipolar charge carrier mobilities.

Four new room-temperature nematic liquid-crystalline (LC) dimers consisting of a wedge-shaped 3,4,5-tridecyloxy gallic ester molecule linked to either cyanobiphenyl, cholesteryl, pentaalkynylbenzene or triphenylene based moieties are reported. Dimers with pentaalkynylbenzene and triphenylene moieties in their room-temperature discotic nematic (ND) mesophase show ambipolar charge carrier mobilities of the order of 10-5 cm2 V-1 s-1 and 10-3 cm2 V-1 s-1, respectively, as measured using a time-of-flight (ToF) technique.

Experimental and theoretical study on photochromism of triphenylvinyl-naphthopyrans

A novel class of dual photo-responsive triphenylvinyl-naphthopyrans (TNPs) have been designed and synthesized by linking a triphenylvinyl fluorophore with the skeleton of 2H-naphthopyran. UV–vis absorption spectral experiments show that TNPs exhibit very rapid color changes and tunable thermal fading rates, which are controlled greatly by the electronic and steric effect of the triphenylene moiety and the 2-aryl rings. In addition, TNPs can emit strong blue fluorescence in aggregate state due to the restriction of intramolecular rotations. Theoretical calculation unveiled that the triphenylethylene moiety can regulate dynamically the photochromic and discoloration rates of TNPs. These findings will greatly promote the rational design and further development of new organic functional materials.

Bottom‐Up Preparation of Twisted Graphene Nanoribbons by Cu‐Catalyzed Deoxygenative Coupling

AbstractGraphene nanoribbons (GNRs) are promising in organic optoelectronic materials, and their properties largely depend on the size, edge, and conformation. Herein, the fully armchair‐edged GNRs (AGNRs) with lengths up to 2.65 nm by using a Cu‐catalyzed deoxygenative coupling as a key step. The resulting AGNRs (2HBT, 3HBT, and 4HBT) possess highly twisted π‐scaffolds, and the torsion angles between the adjacent triphenylene moieties are larger than 32°, as proved by crystallographic analyses. Theoretical and spectroscopic studies show that the butoxy groups endow AGNRs with electron‐rich features, the extension of the π‐system from 2HBT to 4HBT reinforces S0→S1 excitation, and the distortion of the π‐scaffold enhances the fluorescence quantum yield (ΦF). In particular, 4HBT has the lowest oxidation potential (Eox1=0.55 V vs. SCE) and displays red fluorescence with a ΦF value of 81 %.

Functionalized Triphenylene Discotic Molecules: Synthesis and Mesomorphic Characterizations

AbstractWe report the synthesis and characterization of two sets of triphenylene derived discotic molecules with phenol, aldehyde and acid functional groups. In the first set, triphenylene moiety was tethered with benzene derivatives via an ester linkage, while in the second set via an ether linkage with increased aromatic conjugation. All the molecules have triphenylene disc at one end and with benzene, biphenyl and terphenyl cores at the other end connected via flexible methylene spacers. The chemical structures of the novel compounds were confirmed by IR, NMR spectroscopy and CHN analysis methods. Thermal and liquid crystal texture properties were determined using differential scanning calorimetry, polarized optical microscope and X‐ray diffraction studies. Amongst all the novel compounds, only the terphenyl derivative displayed mesomorphism. However, their charge transfer complexes with trinitrofluorenone (TNF) an electron acceptor exhibited columnar mesophases.

Rhodium-Catalyzed Intermolecular Cycloaromatization Route to Cycloparaphenylenes that Exhibit Aggregation-Induced Emission.

A high-yielding new route to substituted cycloparaphenylenes has been developed via reductive aromatization of a diyne bearing two cyclohexadiene units giving a cyclophenylene-ethynylene (CPE) followed by the cationic rhodium(I)/dppe complex-catalyzed intermolecular [2+2+2] cycloaddition (cycloaromatization) of the CPE with monoynes. The thus-obtained products, substituted [8]cycloparaphenylene-triphenylenes ([8]CPPTs), exhibited definite aggregation-induced emission (AIE). This molecule is noteworthy as a novel AIE-active cycloarylene that does not have well-known AIE luminogens, such as tetraphenylethene and 1,2,4,5-tetraphenylbenzene skeletons. The single-crystal X-ray diffraction analyses of the AIE-active [8]CPPTs revealed their highly ordered packing structures in which the rotation of the triphenylene moieties is restricted.

Transition in nanoscale electrical conductivity in the Langmuir-Blodgett film of a novel liquid crystalline oligomer

We have studied the nanoscale electrical conductivity of a monolayer film of a novel star shaped liquid crystalline molecule, hexatriphenylene substituted anthraquinone (AQD6). The molecule has a central core of electron deficient anthraquinone moiety connected to six electron rich triphenylene moieties by flexible alkyl chains. The monolayer formed at air-water interface was transferred onto the solid substrates by Langmuir-Blodgett (LB) technique and its surface topography was imaged using an atomic force microscope (AFM). The limiting area obtained from the surface pressure-area per molecule isotherm and the topography of the AFM images suggest that the anthraquinone moiety of the AQD6 molecule is organized in face-on configuration on the substrate and the triphenylene moieties are in edge-on configuration extended away from the substrate. We have studied the electrical conductivity of the AQD6 monolayer deposited on gold coated silicon substrate using a current sensing AFM. Analysis of current (I) − voltage (V) characteristics of the metal-monolayer film-metal junction showed a transition from direct tunneling to an injection tunneling. Further, we have estimated the barrier height and the effective mass of electron in the metal-monolayer film-metal junction.

Triphenylene: A versatile molecular receptor

Since the late seventies, the search for new molecular receptors has been constant in perfecting the affinity and selectivity of recognition in different media. At present, a renewed interest in (host:guest) chemistry focuses on the molecular detection of specific targets such as biological, pollutant, toxic or explosive species. This review of triphenylene-based receptors outlines their recent contribution to molecular recognition. Two main structural approaches were investigated to transform a simple triphenylene moiety into a host for neutral aromatic compounds or cations, by tailoring multivalent molecules provided with or without a flatten cavity. The properties of different receptors are presented along with the latest synthetic methods to prepare high-value triphenylenes and the perspectives in the field of sensing. In addition, the role of functionalized triphenylenes in extended (host:guest) systems is illustrated by the main examples of discotic liquid crystals and porous coordination polymers involving this polyaromatic compound.

Tuning liquid crystalline phase behaviour in columnar crown ethers by sulfur substituents

Sulfur-containing side chains in the periphery ofo-terphenyl or triphenylene units of crown ethers induce room-temperature columnar mesophases.

Iridium-based emitters containing pendant triphenylene moieties for bluish-green OLEDs with improved efficiency upon thermal annealing

High hole mobility was obtained for iridium complexes bearing triphenylene units, and the annealed emitter shows the best device performance.

Triphenylene–perylene–triphenylene triads with bay-substituents: synthesis, mesomorphism, and electron transfer properties

Three novel triphenylene–perylene–triphenylene triads 5, 6, and 7 with short amido spacer and bay-substituents (H, Br, and tert-butylphenyl) were synthesized in yields of 40–70%. Their structural and conformational characterization had been achieved by FT-IR, NMR, and HR-MS. The studies of liquid crystalline behaviors suggested that triads 5, 6, and 7 possessed hexagonal columnar mesophase. The bay-substituents were favorable for decreasing the phase transitions temperature and enlarging the ranges of phase transfer temperatures. Their absorption spectra were similar to the absorption bands of analogues of triphenylene and perylene. Their fluorescence spectra exhibited strong Dexter electron transfer between triphenylene moiety and perylene moiety, resulting in drastic fluorescence quenching. The larger π–π conjugated system of perylene core enhanced the electron transfer property.

Bowl-shaped Tröger's bases and their recognition properties.

The tris-Tröger's bases (TBs) are electron-rich fluorescent concave receptors due to the incorporation of naphthalene or triphenylene moieties (calix-1 and calix-2). The structures of the TBs were studied using SXRD to reveal the propensity to bind nitroaromatics. Titration with explosive-related nitro-compounds suggests that the TBs may be used for sensing explosives.

Synthesis, photophysical and optoelectronic properties of quinazoline-centered dyes and their applications in organic light-emitting diodes

Quinazoline-centered derivatives with benzoimidazole, carbazole, and triphenylene moieties, were synthesized. Their relationships between electrochemical, photophysical, and optoelectronic properties and structure were discussed in detail. Efficient red phosphorescent organic light-emitting diodes with low turn-on voltage were demonstrated by using them as host materials, and achieved maximum external quantum efficiencies, current efficiencies, and power efficiencies of 19.2%, 18.3 cd/A, 21.7 lm/W for 4-[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl]-2-[3-(tri-phenylen-2-yl)phen-3-yl]quinazoline, of 18.4%, 17.6 cd/A, 19.3 lm/W for 4-(9-phenyl-9H-carbazol-3-yl)-2-[3-(triphenylen-2-yl)phenyl]quinazoline, of 15.6%, 14.4 cd/A, 16.7 lm/W for 2,4-bis[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl]quinazoline, and of 17.4%, 16.7 cd/A, 15.7 lm/W for 2,4-bis(9-phenyl-9H-carbazol-3-yl)quinazoline, respectively. Moreover, improving the electron-injection/transport abilities of host materials could ideally improve the performance of organic light-emitting diodes under low operation voltage, while enhancement of hole-transporting abilities by using bipolar materials could balance the carriers to maintain high efficiency under high operating voltage. These materials exhibited high glass-transition temperature of 146–154 °C and decomposition temperature of 400–447 °C.

Synthesis and thermotropic behavior of side chain polysiloxane bearing triphenylene moiety

Side chain discotic polysiloxane with 2,3,6,7-tetrakis(hexyloxy)-10-methoxytriphenylene-11-undecanoate moi- eties is synthesized by hydrosilylation reaction. The phase behavior and thermooptical properties of the polysiloxane and the side chain precursor 2,3,6,7-tetrakis(hexyloxy)-10-methoxytriphenylene-11-undecanoate are examined by polarizing optical microscopy, thermooptical analysis, differential scanning calorimetry and wide angle X-ray scattering studies. A columnar planar alignment of LC in the layers has been determined. The pronounced alignment makes this polymer a promising material for application in optoelectronic devices. The differences in phase transitions and morphology between the triphenylene precursor and the discotic polysiloxane are discussed.

Spatial Extension of Excitons in Triphenylene-Based Polymers Given by Range-Separated Functionals

Motivated by an experiment in which the singlet–triplet gap in triphenylene-based copolymers was effectively tuned, we used time-dependent density functional theory (TDDFT) to reproduce the main results. By means of conventional and long-range corrected exchange correlation functionals, the luminescence energies and the exciton localization were calculated for a triphenylene homopolymer and several different copolymers. The phosphorescence energy of the pure triphenylene chain is predicted accurately by means of the optimally tuned long-range corrected LC-PBE functional and slightly less accurate by the global hybrid B3LYP. However, the experimentally observed fixed phosphorescence energy could not be reproduced because the localization pattern is different from the expectations: instead of localizing on the triphenylene moiety—which is present in all types of polymers—the triplet state localizes on the different bridging units in the TDDFT calculations. This leads to different triplet emission energies for each type of polymer. Yet, there are clear indications that long-range corrected TDDFT has the potential to predict the triplet emission energies as well as the localization behavior more accurately than conventional local or semilocal functionals.

Ordered nanostructures at two different length scales mediated by temperature: A triphenylene‐containing mesogen‐jacketed liquid crystalline polymer with a long spacer

ABSTRACTA mesogen‐jacketed liquid crystalline polymer (MJLCP) containing triphenylene (Tp) moieties in the side chains with 12 methylene units as spacers (denoted as PP12V) was synthesized. Its liquid crystalline (LC) phase behavior was studied with a combination of solution 1H NMR, solid‐state NMR, gel permeation chromatography, thermogravimetric analysis, polarized light microscopy, differential scanning calorimetry, and one‐ and two‐dimensional wide‐angle X‐ray diffraction. By simply varying the temperature, two ordered nanostructures at sub‐10‐nm length scales originating from two LC building blocks were obtained in one polymer. The low‐temperature phase of the polymer is a hexagonal columnar phase (ΦH, a = 2.06 nm) self‐organized by Tp discotic mesogens. The high‐temperature phase is a nematic columnar phase with a larger dimension (a′ = 4.07 nm) developed by the rod‐like supramolecular mesogen—the MJLCP chain as a whole. A re‐entrant isotropic phase is found in the medium temperature range. Partially homeotropic alignment of the polymer can be achieved when treated with an electric field, with the polymer in the ΦH phase developed by the Tp moieties. The incorporation of Tp moieties through relatively long spacers (12 methylene units) disrupts the ordered packing of the MJLCP at low temperatures, which is the first case for main‐chain/side‐chain combined LC polymers with MJLCPs as the main‐chain LC building block to the best of our knowledge. The relationship of the molecular structure and the novel phase behavior of PP12V has implications in the design of LC polymers containing nanobuilding blocks toward constructing ordered nanostructures at different length scales. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 295–304

Triphenylene containing host materials with high thermal stability for green phosphorescent organic light emitting diode

We report series of triphenylene derivatives with good electronic properties for the use as host materials for green phosphorescent organic light emitting diodes (PHOLEDs). We applied highly planar triphenylene moieties which could provide good electron transport ability and the carbazole or dibenzothiophene moieties which could provide good hole transport ability to obtain a bipolar host materials for green PHOLEDs. From this approach we achieved relatively good current efficiency up to 64 cd/A and external quantum efficiency up to 20.3%, respectively. This was the much more improved value (by ∼22.3%) compare to that obtained from the 4,4′-N,N′-dicarbazolebiphenyl system as a reference.

2,3,6,7,10,11-Hexamethoxytriphenylene (HMTP): A new organic cathode material for lithium batteries

We propose a new organic cathode material for rechargeable lithium battery applications: 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP). HMTP is composed of six methoxy functional groups substituted onto a central triphenylene moiety. The cell, incorporating 40wt.% of organic cathode material, exhibits full specific capacity at current densities up to 3C. The main advantage of HMTP as organic cathode material lies in a stable cell performance and negligible self discharge, even though the capacity is lower, ~66mAh/g, compared to other organic cathode materials. Cells with the HMTP cathode showed >95% retention of the initial discharge capacity after 50cycles at 1C and self-discharge was not observed during a full month of open circuit voltage measurements. The latter is due to the fact that the nature of the HMTP radical is fundamentally different from other organic cathode materials' radicals.

Synthesis and Optical Properties of Triphenylene-Based Dendritic Donor Perylene Diimide Acceptor Systems

A donor-acceptor charge transfer system based on two discotic mesogens has been synthesized. The donor is either a triphenylene (POG0) or a triphenylene-based conjugated dendron (POG1), while the acceptor is a perylene diimide (PDI) core. The donors are covalently linked to the bay positions of the PDI core through an ether linkage. In chloroform, due to the short donor-acceptor distance and the matching frontier orbital levels, photoinduced charge transfer from either the donor excitation or the acceptor excitation are both thermodynamically and kinetically favored, resulting in efficient quenching of both donor and acceptor fluorescence. In a less polar solvent, hexane, while charge transfer is still the dominant mechanism for decay of the excited electronic state of POG1, photoinduced charge transfer is no longer energetically favorable for POG0 when the acceptor PDI core is excited, making the PDI core of POG0 weakly fluorescent in chloroform but strongly so in hexane. In solid film, POG0 is highly aggregated through both PDI-PDI and triphenylene-triphenylene homotopic stacking. POG1, on the other hand, aggregates through triphenylene dendrons with limited PDI-PDI core stacking, presumably due to the steric hindrance caused by bulky triphenylene moieties which block the access to the PDI core. The efficient photoinduced charge transfer, coupled with the homotopic stacking that forms separated electron-transporting PDI-stacked columns and hole transporting triphenylene-stacked columns, suggests that the reported donor-acceptor systems based on dual-discotic mesogens are potentially new efficient photovoltaic materials.

ChemInform Abstract: Charge-Transfer Absorption in Doped Columnar Liquid Crystals.

The optical properties of doped columnar phases formed either by a 1 : 1 mixture of an electron donor [2,3,6,7,10,11-hexa-(n-pentyloxy)triphenylene] and an electron acceptor (2,4,7-trinitrofluoren-9-one) or by a dimer in which the donor (triphenylene moiety) and the acceptor (trifluorenone moiety) are covalently linked are reported and compared with those of the solutions. In concentrated solutions a charge transfer (CT) absorption is observed for both donor–aceptor pairs corresponding to 2.51 and 2.43 eV, respectively. For the 1 : 1 mixture, CT complex formation in solution is greatly favoured by the presence of molecular aggregates. The polarized absorption spectra obtained with oriented thin films reveal that the charge transfer occurs along the alternate donor–acceptor stacking.

Stress-strain relation in the collapse of Langmuir monolayer of a dimer of disk shaped moiety

Langmuir monolayer of a novel molecule containing dimer of disk shaped moiety, viz., terephtalic acid bis-[6-(3,6,7,10,11-pentahexyloxy-triphenylen-2-yloxyl)-hexyl] ester (tp-dimer), was studied at air-water interface. The monolayer of the tp-dimer at air-water interface exhibited the coexistence of condensed and gas phases at large area per molecule which on compression transformed to a uniform condensed phase at lower area per molecule (1.80 nm(2)) and then collapsed at 1.67 nm(2). The monolayer film transferred by Langmuir-Blodgett technique onto a hydrophilic silicon substrate was studied using an atomic force microscope. The topography image showed the film to be of height of about 1.5 nm corresponding to the edge-on configuration of the triphenylene moieties. We have studied the collapse of monolayer at air-water interface as a function of compression rate and temperature. We find that the collapse pressure increased with increase in the compression rate. The surface pressure of the monolayer is considered as stress and compression as strain. The strain rate is related to the collapse pressure by a power law similar to that found in the dendrimers. Our studies on the effect of temperature on the collapse pressure of tp-dimer monolayer showed that the collapse pressure decreased with increase in temperature. We have considered the Arrhenius temperature dependence of the strain rate and calculated the activation energy for the collapse of monolayer. Our analysis of the relative area loss as a function of time in the collapse region suggests that the monolayer collapses by the formation of nuclei of three-dimensional crystallites.