Hexabenzocoronene Research Articles

Aggregation of modified hexabenzocoronenes as models for early stage asphaltene self-assembly

Molecular dynamics simulations were performed on solvated systems containing three molecules of hexabenzocoronene (HBC) derivatives to model the initial self-association of asphaltenes. Specifically, the hexane-modified HBC (HBC6) and those with substitutions containing a side chain with sulphur at three positions (α-H6SA, β-H6SB, and γ-HBCS) and a nitrogen substitution (H6N1) are included. These molecules were solvated with 20 mol% heptane and 80% toluene. Intermediate aggregation states, partial (two molecule clusters), as well as full aggregation of trimer clusters were observed. The conformation of the associated clusters was characterised by π–π stacking, giving the cluster a pre-rod-like shape. The aggregates displayed stability and did not dissociate throughout the course of the simulation (100–530 ns). In particular, the H6SB system showed statistically significant difference in means for both the separation distance and overall interaction energy. H6N1 and H6SA systems differed from the others in terms of electrostatic contributions. To gain a thorough understanding of initial aggregation behaviour and conditions of asphaltenes, additional simulations need to be conducted, in particular those incorporating oxygen substitutions as oxygen is a common heteroatom in crude.

Synthesis of a porphyrin-hexaarylbenzene-hexabenzocoronene triad

The synthesis of a triad consisting of porphyrin and hexabenzocoronene (HBC) units, which are connected via a central hexaarylbenzene (HAB) core, is presented. The ortho substitution pattern at the core results in a close proximity of the two chromophores, which influences their properties such as the intensity ratio of UV-vis absorption bands.

Oxa[7]superhelicene: A π-Extended Helical Chromophore Based on Hexa-peri-hexabenzocoronenes.

A novel π-extended "superhelicene" based on hexa-peri-hexabenzocoronenes (HBCs) has been synthesized by an efficient four-step synthetic procedure starting from diphenyl ether. Comprehensive structural analysis of the helicene was performed by NMR spectroscopy and mass spectrometry measurements together with X-ray analysis. Physicochemical analysis of the superhelicene and suitable HBC references revealed it had outstanding fluorescent features with quantum yields of over 80 %.

Targeting ideal acceptor-donor materials based on hexabenzocoronene

A series of new hybrid donor-acceptor materials based on hexabenzocoronenes (HBC) functionalized with electron donors is investigated by combining a variety of quantum mechanical and molecular dynamic methodologies for use in organic photovoltaic (OPV) devices. Segments of a low band gap alternating copolymer constructed of benzo[1,2-b;3,4-b]dithiophene and thieno[3,4-c]pyrrole-4,6-dione were attached to the conjugated HBC core. The copolymer was chosen for its known high performance in OPVs, and both moieties were singled out due to their exceptional resistance to photo-oxidation, an important requirement for such applications. The macromolecular topology of these systems are expected to induce supra-molecular columns, such as those common to discotic liquid crystals, conducive to the effective percolation of electrons in OPV devices. A challenge with these systems, that of the mixing of the electronic structures of the donor and acceptor moieties that result in excitonic losses and charge recombination, was diminished by trialling a range of linking units. It was found possible to propose ideal donor-acceptor structures with enhanced charge dissociations and transfers in the π-stacking direction for use in OPV and other organic electronic devices.

Potential application of doped hexa-peri-hexabenzocoronene as NH3 gas sensor: a computational investigation

In this study, density functional theory calculations were carried out to investigate the adsorption of NH3 gas on the pristine and B- and Al-doped hexa-peri-hexabenzocoronenes (HBCs). The results indicated that the adsorption of NH3 molecule on pristine HBC is quite weak, while both B- and Al-doped HBCs can strongly adsorb NH3 molecule. The significant increase in band gap was observed in the B-doped HBCs, which confirms the high sensitivity of the B-doped HBCs towards NH3 molecule. Also, our calculations show that pristine HBC cannot detect the presence of NH3 gas. The nature of interactions was characterized by the non-covalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses. Based on the overall results, B-doped HBCs are promising candidates for sensing ammonia molecules.

Superphenylphosphines: Nanographene-Based Ligands That Control Coordination Geometry and Drive Supramolecular Assembly.

Tertiary phosphines remain widely utilized in synthesis, most notably as supporting ligands in metal complexes. A series of triarylphosphines bearing one to three hexa-peri-hexabenzocoronene (HBC) substituents has been prepared by an efficient divergent route. These "superphenylphosphines", P{HBC(t-Bu)5}nPh3-n (n = 1-3), form the palladium complexes PdCl2L2 and Pd2Cl4L2 where the isomer distribution in solution is dependent on the number of HBC substituents. The crystalline structures of five complexes all show intramolecular π-stacking between HBC-phosphines to form a supramolecular bidentate-like ligand that distorts the metal coordination geometry. When n = 2 or 3, the additional HBC substituents engage in intermolecular π-stacking to assemble the complexes into continuous ribbons or sheets. The phosphines adopt HBC's characteristics including strong optical absorption, green emission, and redox activity.

The mechanochemical Scholl reaction - a solvent-free and versatile graphitization tool.

Herein, we report on the mechanochemical Scholl reaction of dendritic oligophenylene precursors to produce benchmark nanographenes such as hexa-peri-hexabenzocoronene (HBC), triangular shaped C60 and expanded C222 under solvent-free conditions. The solvent-free approach overcomes the bottleneck of solubility limitation in this well-known and powerful reaction. The mechanochemical approach allows tracking the reaction process by in situ pressure measurements. The quality of produced nanographenes has been confirmed by MALDI-TOF mass spectrometry and UV-Vis absorption spectroscopy. This approach paves the way towards gram scale and environmentally benign synthesis of extended nanographenes and possibly graphene nanoribbons suitable for application in carbon based electronics or energy applications.

Hierarchically ordered structures of disk-cube triads containing hexa-peri-hexabenzocoronene and polyhedral oligomeric silsesquioxane.

Obtaining nanoscale-ordered structures is important for the development of nanotechnology. We designed and synthesized a series of disk-cube triads containing one hexa-peri-hexabenzocoronene (HBC) and two polyhedral oligomeric silsesquioxane (POSS) moieties, HBC-2POSS. The two POSS units were linked via ester or amide bonds. With the amide linkage used, the hydrogen bonding that was introduced affected the balance between the π-π interaction of HBC cores and crystallization interaction of POSS units. Hierarchically ordered structures were obtained from HBC-2POSS triads owing to the synergistic effect of multiple secondary interactions: π-π interaction, hydrogen bonding, and crystallization interaction. As organic-inorganic hybrid materials, these HBC-2POSS triads are promising candidates for templates <10 nm.

Adsorption properties of chloropicrin on pristine and borazine-doped nanographenes: A theoretical study

Recently, nanographenes were introduced as definite segments of graphene where their end atoms are saturated with hydrogens. In this study, we explored the reactivity and electronic sensitivity of a hexa-peri-hexabenzocoronene (HBC) and newly synthesized borazine-like ring-doped nanographenes (BNG) to the chloropicrin molecule based on density functional theory. We found that chloropicrin is preferentially adsorbed via its N atoms on both HBC and BNG nanographenes. The electronic properties of HBC were predicted to be sensitive to chloropicrin but the adsorption capacity is low because of the small adsorption energy (−7.1 kcal/mol). However, chloropicrin is adsorbed somewhat more strongly on BNG, with an adsorption energy of about −29.9 kcal/mol. After the adsorption of chloropicrin, the lowest unoccupied molecular orbital (LUMO) level of BNG stabilizes and the highest occupied molecular orbital-LUMO gap is decreased by about 85.9%. Thus, BNG converts from a semiconductor into a semimetal with a higher electrical conductivity. The change in electrical conductivity can generate an electrical signal, which is helpful for detecting chloropicrin. In addition, we predicted a short recovery time of 14.6 s at 350 K for this sensor.

FHBC, a Hexa‐peri‐hexabenzocoronene–Fluorene Hybrid: A Platform for Highly Soluble, Easily Functionalizable HBCs with an Expanded Graphitic Core

AbstractMaterials based upon hexa‐peri‐hexabenzocoronenes (HBCs) show significant promise in a variety of photovoltaic applications. There remains the need, however, for a soluble, versatile, HBC‐based platform, which can be tailored by incorporation of electroactive groups or groups that can prompt self‐assembly. The synthesis of a HBC–fluorene hybrid is presented that contains an expanded graphitic core that is highly soluble, resists aggregation, and can be readily functionalized at its vertices. This new HBC platform can be tailored to incorporate six electroactive groups at its vertices, as exemplified by a facile synthesis of a representative hexaaryl derivative of FHBC. Synthesis of new FHBC derivatives, containing electroactive functional groups that can allow controlled self‐assembly, may serve as potential long‐range charge‐transfer materials for photovoltaic applications.

FHBC, a Hexa-peri-hexabenzocoronene-Fluorene Hybrid: A Platform for Highly Soluble, Easily Functionalizable HBCs with an Expanded Graphitic Core.

Materials based upon hexa-peri-hexabenzocoronenes (HBCs) show significant promise in a variety of photovoltaic applications. There remains the need, however, for a soluble, versatile, HBC-based platform, which can be tailored by incorporation of electroactive groups or groups that can prompt self-assembly. The synthesis of a HBC-fluorene hybrid is presented that contains an expanded graphitic core that is highly soluble, resists aggregation, and can be readily functionalized at its vertices. This new HBC platform can be tailored to incorporate six electroactive groups at its vertices, as exemplified by a facile synthesis of a representative hexaaryl derivative of FHBC. Synthesis of new FHBC derivatives, containing electroactive functional groups that can allow controlled self-assembly, may serve as potential long-range charge-transfer materials for photovoltaic applications.

Precursor synthesis strategy for polycyclic aromatic conjugated polymers on the application of supercapacitors

Polycyclic aromatics (PCAs) possess excellent photoelectric properties, but the construction of such compounds has been a quite challenging subject of study, mainly due to very low solubility. Herein we report a precursor synthesis strategy for polycyclic aromatic conjugated polymers. A soluble precursor polymer, that containing fusible “double U-shaped aromatic” (DUA) and perylenetetracarboxydiimide (PDI) units, was firstly synthesized by Suzuki coupling. The stereo aromatic units in polymer backbone were found to be converted into polycyclic aromatic units, i.e. hexa-peri-hexabenzocoronene (HBC), by chemical or electrochemical oxidation, which resulted in a formation of insoluble polycyclic aromatic conjugated polymers. The electrochemical oxidations that occurred at the interface of electrode and solution exhibited higher cyclization reactivity and leads to the formation of high quality films on the electrode surface. Characterization by Raman and UV-visible (UV-Vis) spectroscopy validated the successful formation of this HBC structure. Some potential applications of such thin films are being explored, and here we focus on the characteristics of supercapacitors based on their excellent electrochemical properties.

Synthesis, Photophysical Characterization, and Self-Assembly of Hexa-peri-hexabenzocoronene/Benzothiadiazole Donor-Acceptor Structure.

Hexa-peri-hexabenzocoronene (HBC) substituted by six benzothiadiazole (BTZ) units with ethynylene bridges is synthesized as a new donor-acceptor (D-A) motif. The C≡C bridges significantly reduce the dihedral angles between HBC and BTZ, and thus, lead to a planar molecular conformation as predicted by density functional theory calculations. The optoelectronic properties are investigated by UV/Vis absorption and emission spectroscopies with absorption and emission maxima at 424 and 650 nm, respectively, demonstrating the tunable electronic structures of HBC through the attachment of electron-withdrawing BTZ units. Two-dimensional wide-angle X-ray scattering analysis shows that the molecules self-assemble into liquid-crystalline columns with high stability over a wide temperature range. Scanning tunneling microscopy reveals the formation of ordered bilayers of the D-A molecules with star-shaped structures.

Luminescent Bis-Cyclometalated Gold(III) Complexes with Alkynyl Ligands of Hexaphenylbenzene and Hexabenzocoronene Derivatives and Their Supramolecular Assembly.

A series of luminescent bis-cyclometalated gold(III) complexes with different nuclearities and various alkynyl ligands derived from hexaphenylbenzene (HPB) and hexabenzocoronene (HBC) have been synthesized. The energies of the low-energy metal-perturbed intraligand (IL) π-π*(R-C^N^C) absorptions of the HPB-alkynyl gold(III) complexes have been fine-tuned by attaching various substituent groups to the bis-cyclometalating ligands. Similarly, the metal-perturbed 3 IL [π→π*(R-C^N^C)] emissions of the complexes show energy shifts according to the electronic nature of the bis-cyclometalating ligands. On the contrary, the absorption and emission spectra of the HBC-alkynyl gold(III) complex have been assigned as dominated by the IL transitions of the HBC-alkynyl unit, as supported by transient absorption studies. The supramolecular assembly morphologies of the gold(III) complexes have been studied by TEM and SEM, along with comparisons across different complexes based on the molecular structures, and their assembly processes monitored by concentration-dependent and variable-temperature 1 H NMR spectroscopy studies.

Hierarchical Self-Assembly of Disc-Rod Shape Amphiphiles Having Hexa-peri-hexabenzocoronene and a Relatively Long Rod.

Two disc-rod shape amphiphiles consisting of hexa-peri-hexabenzocoronene (HBC) and a nanosized rodlike mesogen were designed and synthesized. Thermotropic phase behaviors were carefully studied. Despite significant steric mismatch between the discs and rods, hierarchical structures were observed for both disc-rod shape amphiphiles at ambient temperature and upon heating. Molecular packing schemes were proposed and confirmed using the reconstructed electron density maps, molecular dynamics simulation, and direct observation using transmission electron microscope. The results demonstrate that the shape effect is of great importance in the self-assembly of shape amphiphiles.

Ionic Conduction in Poly(ethylene glycol)-Functionalized Hexa-peri-hexabenzocoronene Amphiphiles

Discotic liquid crystals based on hexa-peri-hexabenzocoronenes (HBCs) symmetrically substituted with six poly(ethylene glycol) (PEG) chains and further doped with LiCF3SO3 (LiTf) salt at different [EG]:[Li+] ratios nanophase-separate in domains composed from HBC columns and PEG chains. These model amphiphiles behave as viscoelastic solids with a shear modulus of 5 × 106 Pa and an ionic conductivity of 10–5 S/cm at 373 K. At temperatures below 333 K an ionic superstructure is formed of higher shear modulus (108 Pa) that surrounds the HBC columns and follows the disks in their rotational motion. However, the ionic superstructure impedes ion transport. Substituting the HBC core with two PEG chains breaks the symmetry of the ionic superstructure and increases ionic conductivity by an order of magnitude while retaining a high shear modulus and a viscoelastic response. These findings demonstrate that PEG-functionalized HBCs have great potential as new electrolytes because they combine ionic conductivity with mechanical stability. Moreover, when combined with electronic conduction within the HBC columns, this design can result in structures that exhibit simultaneous electronic and ionic transport.

Detection of NO2 by hexa-peri-hexabenzocoronene nanographene: A DFT study

It has been previously indicated that pristine graphene cannot detect NO 2 gas. Nanographene is a segment of graphene whose end atoms are saturated with hydrogen atoms and its properties are different from those of graphene. Herein, we investigated the reactivity, electronic sensitivity, and structural properties of hexa- peri -hexabenzocoronene (HBC) nanographene toward NO 2 gas using density functional theory calculations. It was found that the central and peripheral rings of HBC are aromatic but the middle rings are non-aromatic, following Clar's sextet rule of aromaticity. The NO 2 molecule prefers to be adsorbed on the central ring with a nitro configuration, releasing an energy of about 13.2 kJ/mol. The NO 2 molecule significantly stabilizes the LUMO level of the HBC, thereby reducing the HOMO–LUMO energy gap from 3.60 to 1.35 eV. This indicates that the HBC is converted from a semiconductor to a semimetal. It was shown that the adsorption of NO 2 gas by HBC can produce an electrical signal selectively in the presence of O 2 , H 2 , N 2 , CO 2 , and H 2 O gases. A short recovery time about 1.9 ns is predicted and the effect of density functional is investigated.

Synthesis of bright red-emissive dicyanoetheno-bridged hexa-peri-hexabenzocoronene dimers.

The introduction of a dicyanomethyl anion group to hexa-peri-hexabenzocoronene (HBC) substantially enhanced the emission properties of HBC due to a large perturbation of its electronic structure. In addition, dicyanoetheno-bridged HBC dimers obtained from oxidation of a dicyanomethyl HBC anion exhibited bright red emission in solution and solid states. Intramolecular charge transfer interactions between the HBC units and the dicyanoethene bridge induced solvatochromic behaviour in their emission spectra. Dicyanoetheno-bridged HBC dimers exhibited cis-trans photoisomerization behaviour in the solution, affording the mixture in cis-isomer dominance in the photostationary state. Theoretical calculations revealed that the cis-isomer is more thermodynamically stable than the trans-isomer.

Diverse configurations of columnar liquid crystals in cylindrical nano- and micropores.

Using 2D X-ray diffraction and AFM we studied the configuration, in cylindrical confinement, of hexagonal columnar phases that anchor homeotropically, i.e. with the columns normal to the pore wall. A wide range of pore diameters, from 20 nm to 100 μm, were explored by employing anodic alumina membranes and glass capillaries. The compounds used were a small discotic, hexakis(hexyloxy)triphenylene (HAT6), a large discotic hexa-peri-hexabenzocoronene (HBC), and a T-shaped bolaamphiphile, forming a honeycomb-type columnar phase. It was found that in pores up to tens of μm in diameter the columns adopt the "logpile" configuration with parallel columns crossing the pore perpendicular to its axis. Starting with 20 nm pores, with increasing pore diameter up to 5 different configurations are observed, the sequence being the same for all three compounds in spite of their structural diversity. One of the {100} planes of the hexagonal logpile starts from being parallel to the pore axis, then rotates by 90° as the pore size increases, and eventually becomes tilted to the pore axis by (8.5 ± 1)° as the pore widens further. Finally, in glass capillaries of tens of μm and beyond, the columns become axially oriented, parallel to the capillary axis. This latter finding was particularly unexpected as common sense would suggest axial columns to be favoured by planar anchoring, where in fact, it was shown to be hard to achieve. The present findings should help in the design of low-dimensional semiconductor or ionic conductor devices based on oriented columnar phases.

A Large π-Extended Carbon Nanoring Based on Nanographene Units: Bottom-Up Synthesis, Photophysical Properties, and Selective Complexation with Fullerene C70.

Herein we report the organoplatinum-mediated bottom-up synthesis, characterization, and properties of a novel large π-extended carbon nanoring based on a nanographene hexa-peri-hexabenzocoronene (HBC) building unit. This tubular structure can be considered as an example of the longitudinal extension of the cycloparaphenylene scaffold to form a large π-extended carbon nanotube (CNT) segment. The cyclic tetramer of a tetramesityl HBC ([4]CHBC) was synthesized by the reaction of a 2,11-diborylated hexa-peri-hexabenzocoronene with a platinum complex, followed by reductive elimination. The structure of this tubular molecule was further confirmed by physical characterization. Theoretical calculations indicate that the strain energy of this nanoring is as high as 49.18 kcal mol-1 . The selective supramolecular host-guest interaction between [4]CHBC and C70 was also investigated.