Triphenylene Research Articles

Radical Ions of a π-Bowl Sumanene: Effects of Strained Structure on the Electronic Transitions.

Strained polyaromatic carbon molecules exhibit interesting properties owing to enhanced interactions between p orbitals of sp2 carbons; sumanene (SUM) is one of these bowl-shaped π-conjugated molecules (π-bowls). In the present study, the radical cation and radical anion of SUM were characterized by radiation chemical methods, that is, pulse radiolysis and γ-ray radiolysis. Absorption spectra of the SUM radical cation and radical anion in a wide spectral region ranging from the visible to near-IR were successfully obtained. Absorption spectra of the SUM radical cation and radical anion are similar in shape to those of the corresponding species of triphenylene (TP), which possesses a planar structure and the same π-electron system as SUM. However, the SUM radical anion showed lower peak shifts than the TP radical anion. Theoretical calculations revealed that the MOs responsible for the electronic transitions of the SUM radical anion are different from those of the TP radical anion, in contrast to the radical cations. These results demonstrate that the strains in the molecular geometries affect the electronic transitions of radical ions.

Controlled synthesis and microstructure tuning of PEG-containing side-chain discotic liquid crystalline block copolymers via RAFT polymerization

Liquid crystalline block copolymers (LCBCPs) are fascinating for their combining molecular level liquid crystalline orders and microphase separated multidomain morphologies. Here in this article, a series of PEG-containing side-chain discotic LCBCPs of PEG-b-Pm-n with variant spacer length m = 6, 10 and degree of polymerization (DP) of discotic LC block from n = 10 to 45, have been well-synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization. The RAFT process mediated by macromolecular chain transfer agent (macroCTA) shows remarkable monomer concentration dependence. The influence of the introduced PEG block on the nano-scale microphase-segregation and mesophase organization is closely related to the side-chain triphenylene (TP) discogens stacking mode dependent on the spacer length. Wherein, the PEG-b-P6-n series with a six-methylene spacer exhibit consistent microphase separation with slightly disturbed yet ordered columnar structures. While for PEG-b-P10-n series with a longer ten-methylene spacer, the columnar organization in the copolymers is even improved in contrast with the low order of randomly TP stacking in their corresponding homopolymers. This work offers a viable and inspiring pathway for controlled synthesis of block copolymers with bulky side groups, as well as enhances in-depth understanding of the hierarchical superstructure organization in discotic units involved complex block copolymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2544–2553

Copper Causes Regiospecific Formation of C4F8‐Containing Six‐Membered Rings and their Defluorination/Aromatization to C4F4‐Containing Rings in Triphenylene/1,4‐C4F8I2 Reactions

The presence of Cu in reactions of triphenylene (TRPH) and 1,4-C4 F8 I2 at 360 °C led to regiospecific substitution of TRPH ortho C(β) atoms to form C4 F8 -containing rings, completely suppressing substitution on C(α) atoms. In addition, Cu caused selective reductive-defluorination/aromatization (RD/A) to form C4 F4 -containing aromatic rings. Without Cu, the reactions of TRPH and 1,4-C4 F8 I2 were not regiospecific and no RD/A was observed. These results, supported by DFT calculations, are the first examples of Cu-promoted 1) regiospecific perfluoroannulation, 2) preparative C-F activation, and 3) RD/A. HPLC-purified products were characterized by X-ray diffraction, low-temperature PES, and (1) H/(19) F NMR.

Well-Organized Columnar Superlattices via Positive Coupling between Polymer Backbone and Discotic Side Groups

Very little is known about some fundamental issues such as the spacer length influence and molecular weight (MW) effect of discotic liquid crystalline polymers (DLCPs), despite the elucidation of such aspects are of crucial importance for their structure tuning and device performance. Here in this article, a systematic comparative study has been conducted to investigate the MW effect and especially gain a deeper insight into the spacer length influence of side-chain DLCPs based on a homologous series of well-defined discotic liquid crystalline polyacrylates with triphenylene (TP) side groups of variant spacer lengths. The series DLCPs of shorter spacers display various well-organized columnar superlattices based on multicolumn bundles organization with “coordination number” from two to six through individual discogens or discrete columnar stack (DCS)-based intracolumnar stacking modes. It is disclosed for the first time that the positive coupling effect (PCE) prevails in side-chain DLCPs, and proper coupling between discotic side groups and polymer backbone is desirable and required for achieving well-organized ordered columnar mesophases, in striking contrast with the renowned classical spacer decoupling principle directing the fruitful exploration of their side-chain calamitic counterparts for several decades. These findings are inspiring for in-depth understanding of self-assembly of aromatic interactions involved complex functional chemical and biological systems and especially opening an avenue for rational design and synthesis of well-controlled side-chain DLCPs for low-cost solution processable optoelectronic device applications.

Trialkylsilylethynyl-substituted triphenylenes and hexabenzocoronenes: highly soluble liquid crystalline materials and their hole transport abilities

Four triphenylene (TP) and four hexa-peri-hexabenzocoronene (HBC) derivatives with trialkylsilylethynyl groups were prepared and characterized by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction measurements. All compounds were highly soluble in less-polar organic solvents and exhibited a columnar phase, Colh or Colr for the TPs, and Colh for the HBCs. The hole transport ability in the HBCs' columnar phase, 0.4–1.5×10−3 cm2 V−1 s−1 at 40−180 °C, and its temperature dependence were determined by the time-of-flight method using a solution technique.

Hierarchical Self-Organization and Uniaxial Alignment of Well Synthesized Side-Chain Discotic Liquid Crystalline Polymers

Liquid crystalline polymers (LCPs) combine the attributes of liquid crystals and polymers, while discotic LCPs have been less developed in sharp contrast to their calamitic counterparts mainly due to lack of suitable discotic LCP materials. Here we successfully prepared a series of well-defined triphenylene (TP) based discotic LC polyacrylates via reversible addition–fragmentation chain-transfer (RAFT) polymerization for the first time, and through a combination of multiple analysis techniques and phase transition kinetics study, a remarkable molecular weight effect or polymer effect at a critical degree of polymerization (DP) around 20 has been disclosed. Moreover, the first proposed discrete columnar stacks (DCS) based hierarchical self-organization model accounts well for the formation and transformation of ordered hexagonal columnar lattice Colho dominated by side-chain TP stacking and oblique columnar superlattice Colob-s induced by compaction and ordering of polymer backbones. The in-depth understanding of their superstructures and readily achieved uniaxial alignment pave the way for the rational design and preparation of such kind of solution processable cutting-edge polymeric semiconducting materials and may boost various fascinating optoelectronic applications.

Supramolecular transformation from ordered columnar to disordered columnar to tetragonal micellar structures in clicked dodeca-alkylated discotic triphenylene liquid crystals

We prepared three discotic liquid crystals (DLCs) based on a triphenylene (TP) disc functionalized with twelve alkyl peripheries. The synthesis of the discogens was performed by a click reaction using Cu(OAc)2 as the catalyst, with six triazolyl groups connecting the TP core with twelve alkyl chains. According to thermal data from differential scanning calorimetry (DSC), discogen , which has the shortest hexyl peripheries, exhibited two LC phases, and and , with decyl and tetradecyl peripheries, respectively, displayed three LC phases as a function of the temperature. Structural analyses using small- and wide-angle X-ray scattering (SAXS and WAXS) techniques revealed ordered and disordered hexagonal columnar LC phases in all the discogens. On the other hand, an unconventional micellar phase with P42/mnm symmetry consisting of thirty micelles was found only in and , when the temperature increased. The thermally induced transformation from the columnar to the micellar phase can be explained by increased chain entropy at higher temperatures. The complex micellar packing in the noncubic phase is attributed to the softness of the DLC micelles because the micellar corona consists of flexible alkyl chains. The discogen design concept in this study (i.e., the introduction of multibranched alkyl peripheries to the discotic mesogens via click chemistry) resulted in unconventional columnar-to-micellar transformation in conventional TP DLCs.

Self-Assembly of Diblock Polythiophenes with Discotic Liquid Crystals on Side Chains for the Formation of a Highly Ordered Nanowire Morphology

Diblock copolymers bearing a triphenylene (TP) discotic liquid crystals moiety, poly(3-hexylthiophene)-block-poly[3-(10-(2,3,6,7,10-pentakis(hexyloxy)triphenylen)-decyloxy)thiophene] (P3HT-b-P3TPT), was successfully synthesized by Grignard metathesis polymerization. The self-assembled nanowire structures of these diblock copolymers have been investigated by atomic force microscopy and transmission electron microscopy. The domain size and crystallinity of the nanostructures can be easily controlled by tuning the P3HT/P3TPT block ratio and by employing different annealing processes such as thermal and solvent annealing. The results of X-ray diffraction indicate that both intermolecular interactions and mesogen packing are essential for the formation of nanostructures in the diblock copolymers. Although the block ratio of P3HT and P3TPT comes to 9:1 and the copolymer undergoes solvent annealing followed by thermal treatment, an optimal crystalline nanowire with a size of 16.9 nm is formed. In addition, solar cells based on these copolymers as electron donors in combination with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or N,N'-di(2-ethylhexyl)perylene-3,4,9,10-tetracarboxylbisimide (PDI) as electron acceptors have been constructed, and the effect of the nanomorphology on device performance has been investigated.

Triphenylenes and Azatriphenylenes by [2+2+2] Cycloadditions

Triphenylenes and Azatriphenylenes by [2+2+2] Cycloadditions

Triphenylene-Based Side Chain Liquid Crystalline Block Copolymers Containing a PEG block: Controlled Synthesis, Microphase Structures Evolution and Their Interplay with Discotic Mesogenic Orders

Triphenylene (TP) derivatives are typical and probably the most widely studied discotic liquid crystalline (DLC) materials. Through polymer analogous reactions to attach TP mesogens to the well-synthesized poly(ethylene glycol)-b-poly(2-hydroxyethyl acrylate) (PEG–PHEA) by ATRP, a series of well-defined side chain DLC diblock copolymers PEG–poly(TPm) (m = 6 or 10) with DLC block weight fraction (fw,DLC) ranging from 37% to 90% have been successfully prepared with narrow molecular weight distribution (PDI ≤ 1.11). An intriguing microphase-separated superstructure evolution and the correlation between overall morphologies and discotic mesogenic orders as a function of fw,DLC and temperature have been demonstrated by combination of DSC, POM, and variable temperature SAXS/WAXS. Those copolymers with lower DLC contents (fw,DLC = 37% and 43%) and at lower temperatures formed lamellar structures of variant periods and underwent order–order transitions upon PEG region crystallization at 45 °C and different discotic mesophases of ND or Ncol transition at about 25 °C. For the copolymer with intermediate fw,DLC = 62%, a high temperature hexagonal packed cylinder (HPC) structure of amorphous PEG nanocylinders in the matrix of DLC was formed above 35 °C, while upon cooling below 35 °C it turned into a mixed lamellar structure with PEG region crystallization. The higher fw,DLC (67% ∼ 80%) copolymers exhibited HPC structures with the DLC matrix showing Ncol or ND mesophases. For copolymers with the highest fw,DLC around 90%, an overall ND phase was developed in sharp contrast to the ordered columnar phase formed by their corresponding DLC homopolymers, which was quite inspiring and might suggest another pathway of attaining this important nematic discotic phase through introducing a suitable copolymerized block. The better understanding of the interrelation of microstructures and discotic mesogenic orders constitutes the key basis for utilizing such type of organic semiconductor materials and could help to guide the design of complex DLC polymer materials with hierarchical structures for variant applications.

Prediction of rate constants for the gas phase reactions of triphenylene with OH and NO3 radicals using a relative rate method in CCl4 liquid phase-system

The kinetics of CCl4 liquid-phase reactions of ten kinds of polycyclic aromatic compounds (PACs) including triphenylene (TP) with NO3 radicals have been investigated at 273K by a relative rate method using naphthalene (NA) as a reference compound. The obtained relative reaction rates of the tested PACs to NA in CCl4 were as follows: 2.57±0.24 (acenaphthene), 2.11±0.30 (2,3-dimethylnaphthalene), 1.21±0.13 (fluoranthene), 0.56±0.07 (fluorene), 1.85±0.19 (1-methylnaphthalene), 1.77±0.12 (2-methylnaphthalene), 0.11±0.03 (1-nitronaphthalene), 1.59±0.23 (phenanthrene), 2.40±0.29 (pyrene), 0.22±0.04 (TP). TP is a semi-volatile PAC with four aromatic rings and it is chemically changed into mutagenic 2-nitrotriphenylene (2-NTP) via the gas-phase OH or NO3 radical-initiated reactions. On the basis of the relative reactivity of the PACs in the CCl4 liquid phase-system, the rate constants of the gas-phase reactions of TP with OH and NO3 radicals at 298K were predicted to be (8.6±1.2)×10−12cm3molecule−1s−1 and (6.6±1.5)×10−29[NO2]cm3molecule−1s−1, respectively. Based on the ambient concentrations of TP and 2-NTP and the obtained rate constant for the reaction of TP with OH radicals, the atmospheric loss rate of 2-NTP was also evaluated.

A complementary disk-shaped π electron donor–acceptor pair with high binding affinity

Hexaazatriphenylene triimides (HAT) have been shown to be a novel class of disk-shaped π electron acceptors that pair with donors with complementary shape and electron demands, such as triphenylene (TP) derivatives. The donor–acceptor (DA) pair forms a strong charge-transfer complex in CH2Cl2 with an association constant of 2.6 × 104 M−1, which is remarkable for a recognition system that is solely based on electrostatic interactions between two π systems. NMR studies, along with molecular modelling, have revealed a complementary charge distribution and an “eclipsed” conformation in the DA complex. The strong DA interaction results in extended alternating DA stacks in the thin film and mesophases.

Donor/acceptor complex of triphenylene and trinitrotoluene on Au(111): a scanning tunneling microscopy study

The co-adsorption of trinitrotoluene (TNT), a typical π-electron acceptor, and triphenylene (TP), a typical π-electron donor, on a Au(111) surface was investigated by in situ Electrochemical Scanning Tunneling Microscopy (ECSTM). DFT calculations proved that parallelly stacked and well-overlapped TP and TNT molecules can form Donor-Acceptor dyads through intermolecular π-π charge transfer, which agree well with the experimental results in the present work.

Triphenylene/carbazole mesogens and their electrochemistry

The synthesis of 10 discotic mesogens is described in which the well-known hexaalkyloxytriphenylene liquid crystalline core has been covalently linked to incorporate one and three carbazole moieties. These modifications have been achieved by the esterification of mono and tris hydroxy triphenylene derivatives with carboxylic acids incorporating 3,6-bisalkylated or 3,6-bisacylated carbazole moieties. The pure compounds are not liquid crystalline and neither are they when doped with TNF, unlike similar materials that were reported previously, where the carbazole moiety was not 3,6-bisalklylated or 3,6-bisacylated, which when doped with TNF did display mesophases. The solution state cyclic voltammetry of selected materials is reported.

Electrochemical Copolymerization of Triphenylene and 3, 4-Ethylenedioxythiophene and Characterization of the Copolymer

A novel conducting copolymer, was successfully achieved by electrochemical oxidation of the monomer mixtures of 3, 4-ethylenedioxythiophene (EDOT) and triphenylene (TP) in the acetonitrile solvent system containing 0.1 mol/L LiClO4. The resulting copolymer possesses the advantages of both polytriphenylene and poly(3, 4-ethylenedioxythiophene), such as good redox activity, considerable fluorescence property and relatively high electrical conductivity. Ultraviolet-visible, FT-IR and scanning electron microscopy were used to characterize and investigate the structure of the copolymers. Fluorescence spectra revealed that the copolymer dissolved in common organic solvents was a good blue light emitter, with a strong emission at 439 nm. All these results indicate that the copolymer films as obtained have many potential applications in various fields, such as organic light-emitting diodes (OLEDs).

ChemInform Abstract: Photoinduced Single Electron Transfer on 5-Aryl-1,2,4-oxadiazoles: Some Mechanistic Investigations in the Synthesis of Quinazolin-4-ones.

The photochemistry of some 5-aryl-3-methoxy- (or 5-aryl-3-phenyl-) 1,2,4-oxadiazoles irradiated in the presence of different sensitizers [such as diphenylacetylene (DAC), 9,10-diphenylanthracene (DAN), or triphenylene (TPH)] or ground-state donors such as triethylamine (TEA) has been investigated. Intermediates arising from breaking of the ring O-N bond develop both into quinazolin-4-ones (by a heterocyclization reaction involving the aryl at the C-5 of the oxadiazole nucleus) and into open-chain products (corresponding to a reduction at the ring O-N bond), in different ratios depending on their structures and photoreaction conditions. A reasonable explanation considers sensitization by photoinduced electron transfer either from the sensitizer in its excited state to the oxadiazole in its ground state or from the electron donor reagent (TEA) to the excited oxadiazole; in both cases an oxadiazole radical anion is formed as a key species from which breaking of the ring O-N bond takes place. Reduction potentials of representative oxadiazoles confirm this hypothesis. Possible applications in the synthesis of variously substituted quinazolin-4-ones are recognized.

Electrochemical Polymerization and Properties of Poly(triphenylene), an Excellent Blue-Green-Light Emitter

Semiconducting polytriphenylene (PTP), a bright blue-green-light emitter, with good electrochemical behavior, excellent thermal stability, and the electrical conductivity of 10−3 S cm−1 was synthesized successfully by direct anodic oxidation of triphenylene (TP) in different media. The oxidation potential onset of TP in boron trifluoride diethyl etherate containing 3% concentrated sulfuric acid (SA) was reduced to 0.94 V, compared with other electrolyte media. The possible structure of the obtained PTP was investigated by ultraviolet−visible spectroscopy, Fourier transform infrared spectroscopy, and 1D and 2D NMR techniques, respectively. The results showed that the PTP was grown via the coupling of the monomer mainly at the meta position of the benzene ring in TP. Fluorescence spectra indicated that the electrochemically polymerized PTP was an excellent blue-green-light-emitting material with fluorescence quantum yield as high as 0.43. In addition, the morphology and thermal stability of the polymers were also explored by means of scanning electron microscopy and thermal analyzer. The average molecular weight (19 980 g mol−1) and its polydispersity of dedoped PTP were determined by gel permeation chromatography.

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.

Trace Detection of Triphenylene by Surface Enhanced Raman Spectroscopy Using Functionalized Silver Nanoparticles with Bis-Acridinium Lucigenine

Surface enhanced raman scattering (SERS) of triphenylene (TP) has been recorded on Ag nanoparticles functionalized with the molecular assembler bis-acridinium lucigenine dication (LG) which approaches the adsorbate to the metal surface allowing for its detection. Structural information on the host and the analyte can be extracted from the SERS spectra of LG and LG/TP complex. The acridinium planes in LG are staggered, so cavities into which hydrophobic TP can be allocated are created. Moreover, the orientation of LG with respect to the metal surface changes from tilted to perpendicular when concentration of TP increases. However, perpendicular orientation of TP with respect to the metal surface is preferred according to the in-plane enhanced bands recorded in the SERS spectrum. The dependence of the Raman signal of TP on LG concentration has been checked, and trace concentrations of TP have been detected by this technique which therefore can be used as a chemical sensor of organic pollutants.

Measurements and Prediction of Electronic Properties of Discotic Liquid Crystalline Triphenylenes and Phthalocyanines

Objective of this study is the measurement and prediction of the effect of structural changes on the electronic properties of discotic liquid crystals (DLCs), an emerging class of organic semiconductors. Relative changes in frontier orbital energies of potentially discotic triphenylene (TP) and phthalocyanine (Pc) derivatives with different substitution patterns and substituents were predicted by gas phase molecular orbital calculations at a density functional theory (DFT) level. Calculations were performed with different basis sets and obtained frontier orbital energies are compared with experimental data of TP and Pc derivatives that have been studied by cyclic voltammetry (CV) and UV-Vis spectroscopy. Particular interest was given to a possible transition from p-type to n-type properties. A LUMO energy of 4.0 eV is used as reference point because this or lower LUMO energies have been proposed to provide potentially air stable n-type organic materials.