Triphenylene Moieties Research Articles

Designing Lower Critical Solution Temperature Behavior into a Discotic Small Molecule

Design and analysis of amphiphilic small molecules exhibiting lower critical solution temperature (LCST) behavior is reported. 2,3,6,7,10,11-Hexakis[2-(N,N-dialkylamino)ethoxy] triphenylenes containing hydrophilic groups attached at their discotic core were prepared, and the LCST behavior of their solutions was studied using fluorescence spectrophotometry and 1H NMR spectroscopy. 1H NMR spin−lattice relaxation times were used to assess the rotational mobility of molecules below and above the clouding point. The impact on the LCST of supramolecular π−π stacking forces introduced by the triphenylene (TP) core was studied. The operation of the LCST phenomenon was found not to depend significantly on stacking of TP moieties. This process in small molecular species offers several advantages over the polymer-originated phenomenon. For instance, enabling an analogue of the LCST transition in dye molecules might allow the design of novel optical devices by permitting previously unavailable specific aggregated states.

Novel Benzene-Bridged Triphenylene-Based Discotic Dyads

We report the synthesis and characterization of two series of novel triphenylene-based benzene-bridged symmetric discotic dimers. Two triphenylene discotics have been connected to a rigid benzene ring via flexible methylene spacers. In one series, triphenylene moiety was tethered with benzene via an ester linkage, while in the second series it is via an ether linkage. Within each series, the orientation of the linkage of the triphenylene core around the benzene core has been changed by substituting the benzene ring at o-, m-, and p-positions. These materials have been characterized from their spectral and elemental analysis. The thermotropic liquid crystalline properties were investigated by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction studies. All the virgin compounds do not display any mesomorphism; however, their charge transfer complexes with trinitrofluorenone, an electron acceptor, exhibited columnar mesophases. The direct current (dc) conductivity of charge transfer complexes at two ratios has been studied at variable temperature. The small conductivity value demonstrates that long spacers as well as connectivity to the rigid benzene ring dilute the column packing, hence making pi-pi interaction less efficient for the entire column length. A hexagonal assembly of triphenylene-benzene dimer 12 on a highly oriented pyrolytic graphite (HOPG) surface has been visualized with scanning tunneling microscopy (STM).

One-dimensional Stacks of Triphenylenes Stabilized by a Peripheral Hydrogen-bonding Network

Abstract Triphenylenes bearing chiral amide termini were found to form self-assembled nanofibers by the combination of π–π stacking of triphenylene moieties with a hydrogen-bond network of amide terminates.

Columnar Stacks of Star- and Tadpole-Shaped Polyoxazolines Having Triphenylene Moiety and Their Applications for Synthesis of Wire-Assembled Gold Nanoparticles

We report on synthesis, association behavior, and application of six-arm star-shaped and tadpole-shaped amphiphilic polyoxazolines from triphenylene initiators. We synthesized two kinds of novel triphenylene initiators: 2,3,6,7,10,11-hexa(6-bromohexyloxy)triphenylene (initiator for star-shaped polyoxazoline) and 2-(6-bromohexyloxy)-3,6,7,10,11-pentahexyloxytriphenylene (initiator for tadpole-shaped polyoxazoline). Ring-opening cationic polymerization of 2-methyl-2-oxazoline from these initiators successfully produced star- and tadpole-shaped polyoxazolines. Both the star- and tadpole-shaped polyoxazolines formed supramolecular associations in aqueous media due to π−π stacking of hydrophobic triphenylene moiety. Critical micelle concentrations (CMCs) and amounts of π−π stacking of the star- and tadpole-shaped polyoxazolines in aqueous media were investigated by 1H NMR and fluorescence measurements. From tapping mode atomic force microscopy (TM-AFM) measurements, the star-shaped polyoxazolines formed straig...

Single-crystalline Gold Nanodisks Prepared by the Shape Transformation under UV Irradiation from Nanoparticles Protected with Discotic Liquid Crystalline Ligands

Abstract In this paper, we investigated a convenient shape transformation of gold nanoparticles to nanodisks by UV irradiation in chloroform with the aid of protective agents carrying a triphenylene moiety, which absorbs UV energy and plays a role as a mask in directing the deposition of gold atoms at aspecific position.

18,18′-Dihexyl[9,9′]biphenanthro[9,10-b]triphenylene: Construction and Consequences of a Profoundly Hindered Aryl−Aryl Single Bond

The title compound, 1-Hex, was synthesized by the Zr-mediated biphenylation of 4,4'-dihexyloctabromobiphenyl using (Li(THF)4)2 x Zr(biphe)3, where biphe is the 2,2'-biphenyldiyl ligand, in 5% isolated yield. Two independent X-ray diffraction analyses revealed that arene 1-Hex possesses a highly strained and hindered aryl-aryl single bond. This bond causes the phenanthro[9,10-b]triphenylene (PTP) moieties to twist (anthracene subunit dihedral, 69 degrees); the interlocked, helical, homochiral PTP moieties give rise to effective D2 symmetry. The calculated adiabatic homolytic bond dissociation energy of this strained bond is only 67 kcal/mol, but nonetheless the bond exhibits a surprisingly normal length (1.49 A); the reason is elongation only slowly releases strain. Variable temperature NMR revealed two dynamic processes: hexyl rotation (12.0 +/- 0.4 kcal/mol) and inversion of chirality (15.2 +/- 0.6 kcal/mol). DFT calculations provide rate-determining transitions states, whose energies agree with measured values, and provide insight to the mechanism of these processes. Rotation about the central bond is not involved in either observed process. Calculations demonstrate that rotation does not involve a simple torsion of the equilibrium structure, but rather a complex movement with a barrier of 49 kcal/mol from a slipped-parallel, C(2h) intermediate.

Control of Stripelike and Hexagonal Self-Assembly of Gold Nanoparticles by the Tuning of Interactions between Triphenylene Ligands

We describe the self-assembly of gold nanoparticles (Au NPs) protected with newly synthesized discotic liquid crystalline molecules of hexaalkoxy-substituted triphenylene (TP) in mixed toluene/methanol solvent. The stripelike (i.e., 2D consisting of linear 1D in stripe) self-assembly is realized successfully by the aid of pi-pi stacking of TP ligand on Au NPs. The smaller Au NPs with TP (AuTP) or the longer alkyl chain between TP and the gold core provide more free spaces among TP moieties. These spaces allow easy insertion of TP on adjacent AuTPs to lead an interparticle pi-pi interaction to form the stripelike arrangement. The solvent hydrophilicity can also serve as a controlled index to tune arrangement among stripelike, hexagonal close packed (hcp), or disorder. We have changed the solvent hydrophilicity by changing the ratio of methanol to toluene, which affects the balance of solution of AuTP (in toluene) and deposition (in methanol). The larger space between TPs and appropriate solvent hydrophilicity realize stripelike self-assembly caused by a strong pi-pi interaction between TPs, which was characterized by TEM, as well as fluorescence, dynamic light scattering, and 1H NMR spectra.

Discotic‐Functionalized Nanomaterials

Single‐walled carbon nanotubes (SWNTs) and gold nanoparticles (GNPs) were functionalized with triphenylene moiety. These triphenylene‐functionalized nanomaterials were dispersed into the supramolecular order of hexaalkoxytriphenylene derivatives. The functionalized‐nanomaterials‐discotic liquid crystal composites were studied by polarizing optical microscopy, differential scanning calorimetry and X‐ray diffractometry. Our results indicate inclusion of SWNTs and GNPs into the discotic liquid crystalline matrix.

Mesomorphism of Hybrid Siloxane-Triphenylene Star-Shaped Oligomers

Novel hybrid triphenylene-carbosiloxane liquid crystalline monomers and star-shaped oligomers have been synthesized and their thermal behavior and liquid-crystalline properties analyzed and characterized. All compounds exhibit a columnar hexagonal phase and show, particularly the oligomers, a small tendency to crystallize. The substitution pattern on the central triphenylene moiety has very different effects on the crystal to columnar phase and columnar to isotropic liquid-phase transitions. A novel sterically induced superlattice has been found, and a model for the microscopic structure is proposed. One compound could be mechanically aligned, leading to well-oriented columnar liquid crystals.

Synthesis and characterization of photoelectronic polymers containing triphenylamine moiety

Several polymers containing triphenylene moieties in main chain were synthesized by Knovenagel or Wittig condensations. The polymers were characterized by 1H NMR, IR, GPC, TG, UV–vis, FL and CV. Results indicated that PNB, which was prepared from the polycondensation of 4,4′-dialdehyde-4″- n-butyltriphenylamine with 1,4-bis(triphenylphosphonionmethyl)benzene dibromide, is the most thermally stable one and that PNP, which was prepared from the polycondensation of 4,4′-dialdehyde-4″- n-butyltriphenylamine with p-phenylene diacetonitrile, is the most thermally instable one. The fluorescence quantum efficiency of PNB is 94.3%, which is a high value for optoelectronic polymer materials. All the polymers have a similar CV curve with a reversible oxidation peak and two reduction peaks except that PNB has a single reduction peak.

Synthesis and characterization of novel imidazolium-based ionic discotic liquid crystals with a triphenylene moiety

Two novel triphenylene-tethered imidazolium salts were synthesized either by the quaternization of 1-methylimidazole with an ω-bromo-substituted triphenylene or by the quaternization of a triphenylene-substituted imidazole with methyl iodide. Their chemical structures were determined by 1H NMR, 13C NMR, IR, UV spectroscopy and elemental analysis. The thermotropic liquid crystalline properties of these salts were investigated by polarizing optical microscopy and differential scanning calorimetry. These triphenylene-based imidazolium salts with bromide or iodide as counterion show columnar mesophase properties over a wide temperature range.

Discotic Liquid Crystalline Poly(propylene imine) Dendrimers Based on Triphenylene

The design, synthesis, and mesomorphic properties of a new series of homodendrimers consisting of the commercially available poly(propylene imine) (PPI) dendrimers (G = 1-5), PPI-(NH(2))(n)() (n = 4, 8, 16, 32, 64), functionalized with a discotic triphenylene moiety are reported. The liquid crystalline behavior was investigated by means of differential scanning calorimetry (DSC), polarizing-light optical microscopy (POM), and X-ray diffractometry (XRD). All of the homodendrimers showed mesomorphic properties, with the second to fifth generations giving a hexagonal columnar mesophase (Col(h)) and the first generation a rectangular columnar mesophase (Col(r)). The X-ray study reveals that these mesophases show a highly ordered structure with segregation of triphenylenes and dendrimers into separate columns and a regular stacking distance inside the triphenylene columns. GPC analysis showed that the dendrimers had good monodispersity and MALDI-TOF studies of the first three generations gave good evidence that all of the terminal amino groups of the dendrimers were functionalized with a discotic unit.

Fluorescent Coordination Networks of 2,3,6,7,10,11-Hexakis(phenylthio)triphenylene and Silver(I) Triflate

The polycyclic aromatic ligand 2,3,6,7,10,11-hexakis(phenylthio)triphenylene (HPhTT) coordinates with AgTf (Tf = trifluoromethylsulfonate) to form 1D networks with various solvent molecules included. In particular, the crystal structures and photoluminescent properties of compound 1 (formula = 2HPhTT.3AgTf.3toluene) and compound 2 (formula = 2HPhTT.3AgTf.2THF) are described. Both 1 and 2 feature similar network connectivity as well as similar local coordination environments around the silver(I) atoms. The organizations of the guest molecules in the two structures are, however, quite different: In 1, the toluene molecules are enclathrated in isolated cavities by the host network; in 2, the THF molecules are confined in continuous 1D channels. Because of the large aromatic system of the triphenylene moiety, strong fluorescent bands (room temperature) are observed for HPhTT, 1 and 2, with lambda(F,max) = 447 nm for HPhTT and lambda(F,max) = 440 nm for both 1 and 2.

Carbon−Carbon Bond Formation and Cleavage in the Dimerization of a Nickelacycle

Addition of 1,12-dilithiotriphenylenediyl to L2NiCl2 (L = PEt3) gives the nickelacycle L2Ni(1,12-triphenylenediyl), which decomposes to a dimer (L2Ni2C36H20) containing two coupled triphenylene moieties with a new C−C bond. Thermolysis of the dimer completes the coupling, yielding a chiral tetraphenylene, while alkyne addition leads to cleavage of the newly formed C−C bond of the dimer and cycloaddition of the alkyne to the triphenylene fragment.

A new form of discotic metallomesogens: the synthesis of metal-bridged triphenylene discotic dimers

Discotic metallomesogens are becoming increasingly important due to their electronic and optoelectronic properties. Preliminary results on the synthesis and characterization of a new form of discotic metallomesogens in which a Hg atom is covalently linked with two substituted triphenylene moieties are presented.

Synthesis of Discotic Columnar Side-Chain Liquid Crystalline Polymers by Ring-Opening Metathesis Polymerization (ROMP)

Discotic liquid crystalline polymers bearing alkoxy-substituted triphenylene moieties in the side-chain were synthesized by ring-opening metathesis polymerization using a well-defined ruthenium initiator. To elucidate the effect of backbone flexibility on the mesomorphism, norbornene and cyclobutene monomers containing triphenylene moieties were synthesized, which yielded the relatively rigid poly(norbornene)s and the more flexible poly(butadiene)s, respectively, after polymerization. To further increase the backbone flexibility, the poly(butadiene)s were hydrogenated using Crabtree's catalyst to yield triphenylene-substituted poly(butane)s. The mesomorphic behavior of the polymers has been investigated by differential scanning calorimetry (DSC) and powder diffraction X-ray scattering (wide angle X-ray scattering, WAXS). All polymers bearing a 2,3,6,7,19-pentakis(decyloxy)triphenylene-based mesogenic unit exhibit enantiotropic discotic hexagonal mesophases, while the pentoxy analogues do not display liquid crystalline behavior. No effect of backbone rigidity on the mesomorphism could be detected.

Conductivity and photoconductivity of undoped and doped Langmuir‐Blodgett films of a polymer with hexaalkoxytriphenylene side‐groups

AbstractLangmuir‐Blodgett films from a polymer with triphenylene moieties in the side groups deposited on a quartz substratum with aluminium and gold electrodes show a dark conductivity in the plane of the Langmuir‐Blodgett film. This dark conductivity is increased using gold electrodes as compared with aluminium electrodes. It depends in a superlinear way upon the applied electric field and is not enhanced by oxygen. The dark conductivity can be enhanced by doping the Langmuir‐Blodgett films with iodine but it is not influenced by doping the Langmuir‐Blodgett films with 2,4,7‐trinitro‐9‐fluorenone. Upon excitation in the absorption band of the triphenylene moiety an in‐plane photocurrent, which is enhanced by oxygen, could be observed. Also the photocurrent is enhanced by using gold electrodes. Doping the Langmuir‐Blodgett films with iodine or 2,4,7‐trinitro‐9‐fluorenone quenches the photocurrent. Up to 10 W/m2 the photocurrent depends linearly upon the intensity of the incident light.

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.

Electroactive charge-transfer polymers from anodic coupling of dibenzo-crown ethers Part II. Influence of the complexing properties of the polyether rings

A new family of electroactive redox polymers with triphenylene moieties linked two-dimensionally via polyether bridges, has been synthesized by anodic oxidation of dibenzo-crown ethers. The influence of the complexing properties of the polyether rings towards alkali metal cations and neutral guests were studied with regard to the electrochemical behaviour of the monomers themselves, as well as to the ionophoric properties of the polymers.