Polyaromatic Core Research Articles

Peri-Fused polyaromatic molecular contacts for perovskite solar cells.

Molecule-based selective contacts have become a crucial component to ensure high-efficiency inverted perovskite solar cells1-5. These molecules always consist of a conjugated core with heteroatom substitution to render the desirable carrier-transport capability6-9. So far, the design of successful conjugation cores has been limited to two N-substituted π-conjugated structures, carbazole and triphenylamine, with molecular optimization evolving around their derivatives2,5,10-12. However, further improvement of the device longevity has been hampered by the concomitant limitations of the molecular stability induced by such heteroatom-substituted structures13,14. A more robust molecular contact without sacrificing the electronic properties is in urgent demand, but remains a challenge. Here we report a peri-fused polyaromatic core structure without heteroatom substitution that yields superior carrier transport and selectivityoverconventional heteroatom-substitutedcore structures. This core structure produced a relatively chemically inert and structurally rigid molecular contact, which considerably improved the performance of perovskite solar cells in terms of both efficiency and durability. The champion device showed an efficiency up to 26.1% with greatly improved longevity under different accelerated-ageing tests.

Modifying the Substrate-Dependent Pd/Fe2O3 Catalyst-Support Synergism with ZnO Atomic Layer Deposition.

Low-loading Pd supported on Fe2O3 nanoparticles was synthesized. A common nanocatalyst system with previously reported synergistic enhancement of reactivity that is attributed to the electronic interactions between Pd and the Fe2O3 support. Fe2O3-selective precoalescence overcoating with ZnO atomic layer deposition (ALD), using Zn(CH2CH3)2 and H2O as precursors, dampens competitive hydrogenation reactivity at Fe2O3-based sites. The result is enhanced efficiency at the low-loading but high reactivity Pd sites. While this increases catalyst efficiency toward most aqueous redox reactions tested, it suppresses reactivity toward polyaromatic core substrates. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) show minimal electronic impacts for the ZnO overcoat on the Pd particles, implying a predominantly physical site blocking effect as the reason for the modified reactivity. This serves as a proof-of-concept of not only stabilizing supported nanocatalysts but also altering reactivity with ultrathin ALD overcoats. The results point to a facile ALD route for selective enhancement of reactivity for low-loading Pd-based supported nanocatalysts.

Novel Structural Aspects of Heavy-Crude-Derived Asphaltene Molecules for Investigating the Crude Mix Processability in Refinery Operation

Summary In this paper, we investigate the role of asphaltenes derived from heavy crudes, which dictates the behavior of crude mix properties for hassle-free downstream refinery operation. Combined characterization techniques such as proton nuclear magnetic resonance (1H-NMR), cross-polarization magic-angle-spinning carbon-13 (CP/MAS 13C)-NMR, heteronuclear single-quantum coherence (HSQC), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) are used for the detailted study of Ratwai and Ras Gharib (RG)-derived asphaltenes to validate their structural role in selecting the optimal crude mix. As per our investigation, when the polyaromatic core of asphaltene structures are less substituted, the availability of aromatic hydrogen is more; it exhibits a stable crude mix as compared to heavy crudes that have more aromatic core substitution, despite the crudes possessing similar asphaltene content and physicochemical properties. This finding is further extended to West Canadian (WC) and Belayim (BL) heavy crudes for operational suitability. In this study, the key feature is to develop a CP/MAS 13C-NMR-based robust and quick characterization technique that could potentially become a prescreening method to assess crude oil compatibility and its various blend processability in the refinery system. Other characterization techniques, such as 1H-NMR, HSQC, FTIR, TGA, and XRD, would corroborate and confirm the reliability of the data obtained by CP/MAS 13C-NMR.

Forcing Twisted 1,7‐Dibromoperylene Diimides to Flatten in the Solid State: What a Difference an Atom Makes

AbstractPerylene diimides (PDI) are workhorses in the field of organic electronics, owing to their appealing n‐semiconducting properties. Optimization of their performances is widely pursued by bay‐atom substitution and diverse imide functionalization. Bulk solids and thin‐films of these species crystallize in a variety of stacking configurations, depending on the geometry of the stable conformation of the polyaromatic core. We here demonstrate that 1,7‐dibromo‐substituted perylene diimides, PDI(H2Br2), possessing a heavily twisted conformation in the gas phase, in solution and in the solids, can be easily flattened in the solid state into centrosymmetric molecules if the polyaromatic cores form π–π stabilized chains. This is achieved by using axial residues with low stereochemical hindrance, as guaranteed by a single CH2/NH spacer directly linked to the imide function. Structural powder diffraction and DFT calculations on four newly designed species of the PDI(H2Br2) class coherently show that, thanks to the flexibility of the N−X−Ar link (X=CH2/NH), flat cores are indeed obtained by overcoming the interconversion barrier between twisted atropoisomers, of only 26.5 kJ mol−1. This strategy may then be useful to induce “anomalously flat” polyaromatic cores of different kinds (substituted acenes/rylenes) in the solid state, towards suitable crystal packing and orbital interactions for improved electronic performances.

Forcing Twisted 1,7-Dibromoperylene Diimides to Flatten in the Solid State: What a Difference an Atom Makes.

Perylene diimides (PDI) are workhorses in the field of organic electronics, owing to their appealing n-semiconducting properties. Optimization of their performances is widely pursued by bay-atom substitution and diverse imide functionalization. Bulk solids and thin-films of these species crystallize in a variety of stacking configurations, depending on the geometry of the stable conformation of the polyaromatic core. We here demonstrate that 1,7-dibromo-substituted perylene diimides, PDI(H2 Br2 ), possessing a heavily twisted conformation in the gas phase, in solution and in the solids, can be easily flattened in the solid state into centrosymmetric molecules if the polyaromatic cores form π-π stabilized chains. This is achieved by using axial residues with low stereochemical hindrance, as guaranteed by a single CH2 /NH spacer directly linked to the imide function. Structural powder diffraction and DFT calculations on four newly designed species of the PDI(H2 Br2 ) class coherently show that, thanks to the flexibility of the N-X-Ar link (X=CH2 /NH), flat cores are indeed obtained by overcoming the interconversion barrier between twisted atropoisomers, of only 26.5 kJ mol-1 . This strategy may then be useful to induce "anomalously flat" polyaromatic cores of different kinds (substituted acenes/rylenes) in the solid state, towards suitable crystal packing and orbital interactions for improved electronic performances.

Effect of asphaltenes structure on interfacial properties: A dissipative particle dynamics study

Asphaltenes are important components of crude oil that stabilize oil-water emulsions. Due to their complex molecular nature, the connections between molecular structure and interfacial properties of asphaltenes remain unclear. In this work, the effects of polyaromatic cores size, length and the number of aliphatic side chains, and heteroatoms on the structural properties of asphaltenes in oil–water system are investigated by dissipative particle dynamics (DPD). The results show that the asphaltene molecules with larger aromatic cores are better for reducing the interfacial tension (IFT) of the system. The relationship between the interfacial activity of asphaltenes and the length of aliphatic side chains is not monotonic as the concentration increases. Asphaltene molecules with intermediate length and shorter length aliphatic side chains are effective in reducing IFT at lower and higher concentrations, respectively. The asphaltenes with more aliphatic side chains contribute more to the reduction of IFT at lower concentrations, but the side chains can hinder the adsorption of asphaltenes at the interface, which is not conducive to the stability of the system at higher concentrations. In addition, oxygen atoms in the molecular structure of asphaltenes are the key factors that promote the adsorption of asphaltenes to the interface and reduce the IFT. This detailed investigation of the behavior of asphaltenes would be useful to understand the role of asphaltenes in the formation of oil–water emulsions.

Alternation of asphaltene binding arrangement in the presence of chemical inhibitors: Molecular dynamics simulation strategy

Asphaltene deposition is one of the challenging issues in petroleum production and transportation. Chemical inhibitors are commonly employed to mitigate the asphaltene aggregation, which is the primary stage in controlling asphaltene deposition. Design and selection of an effective chemical inhibitor have always been a challenge for the industry, considering substantial variations in characteristics and structures of asphaltene and petroleum. The chemical inhibitors interact with the asphaltene aggregation by alternating their binding arrangement, which is a key factor in the aggregate stability. Molecular studies that can reveal the main mechanisms are still scarce, and the available investigation techniques in this area need significant improvements. Therefore, in this work, molecular dynamics (MD) simulation is employed as a cost-effective and reliable method to study the impact of chemical inhibitors on the binding arrangement of two asphaltene structures. One asphaltene structure contains a hydroxyl group and pyridinic nitrogen in its polyaromatic core, while another lacks both groups. The chemical inhibitors are octylphenol (OP), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), and 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). The simulation results show OP cannot stop the quadrupole–quadrupole interactions between the asphaltenes since the force between OP’s benzene ring and asphaltene polyaromatic core is weaker than the force between the two polyaromatic cores. Nevertheless, OP forms a hydrogen bond with the asphaltene and prevents asphaltene molecules from approaching each other by providing steric hindrance around the molecules. As a result, OP does not show a promising potential to reduce the parallel stacking, especially for the asphaltene with no hydrogen bond potential, while it relatively reduces the T-shape arrangement for both asphaltenes. Ionic liquids (ILs) beat the quadrupole–quadrupole interactions between the asphaltene cores with cation-quadrupole force and notably reduce the parallel stacking. They also lower the number of T-shape binding arrangements between the asphaltene molecules. This research reveals the mechanism for the studied inhibitors to interfere with the asphaltene aggregation based on their functional groups. We introduce new criteria to distinguish different arrangements. The binding arrangement of polyaromatic compounds (such as asphaltene) are not only important in the petroleum industry but also play a crucial role in designing optical and electronic nanodevices. The introduced approach is a new pathway to improve the design of chemical materials to either inhibit or promote aggregation by changing binding arrangement of polyaromatic compounds.

Transparent Liquid Crystal Hole‐Transporting Material for Stable Perovskite Solar Cells

Hexakis(hexyloxy)triphenylene (HAT6) discotic liquid crystal is employed as a transparent hole‐transporting material (HTM) for perovskite solar cells (PSCs) and a power conversion efficiency (PCE) of 15.7% is obtained, which is the highest using HAT6 type of HTMs. Despite lower PCE than spiro‐OMeTAD‐based devices (20.3%), the PSCs based on HAT6 exhibit much higher ambient and thermal stability. A fused polyaromatic core with six alkyl chains leads to high hydrophobicity, and the π‐stacked molecular columns of the HAT6 shield the bis(trifluoromethane)sulfonamide lithium salt dopant migration into the perovskite absorber. The PSCs (under N2 condition) exhibit superior stability compared to the devices employing spiro‐OMeTAD, retaining nearly 92% of their initial efficiency after 1200 h operation. Under ambient conditions, HAT6‐based hole‐transportation layer devices retain 93% of the initial efficiency for 690 h. Under continuous thermal stress of 85 °C, the devices based on HAT6 retain 95% of the initial PCE. The results demonstrate the time applicability of liquid crystal for stable PSCs fabrication.

Influence of Asphaltene Modification on Structure of P3HT/Asphaltene Blends: Molecular Dynamics Simulations.

Further development and commercialization of bulk heterojunction (BHJ) solar cells require the search for novel low-cost materials. The present study addresses the relations between the asphaltenes’ chemical structure and the morphology of the poly(3-hexylthiohene) (P3HT)/asphaltene blends as potential materials for the design of BHJ solar cells. By means of all-atom molecular dynamics simulations, the formation of heterophase morphology is observed for the P3HT-based blends with carboxyl-containing asphaltenes, as well as the aggregation of the asphaltenes into highly ordered stacks. Although the π–π interactions between the polyaromatic cores of the asphaltenes in solutions are sufficient for the molecules to aggregate into ordered stacks, in a blend with a conjugated polymer, additional stabilizing factors are required, such as hydrogen bonding between carboxyl groups. It is found that the asphaltenes’ aliphatic side groups may improve significantly the miscibility between the polymer and the asphaltenes, thereby preventing the formation of heterophase morphology. The results also demonstrate that the carboxyl-containing asphaltenes/P3HT ratio should be at least 1:1, as a decrease in concentration of the asphaltenes leads to the folding of the polymer chains, lower ordering in the polymer phase and the destruction of the interpenetrating 3D structure formed by P3HT and the asphaltene phases. Overall, the results of the present study for the first time reveal the aggregation behavior of the asphaltenes of varying chemical structures in P3HT, as well the influence of their presence and concentration on the polymer phase structure and blend morphology, paving the way for future development of BHJ solar cells based on the conjugated polymer/asphaltene blends.

Tuning interfacial charge transfer in atomically precise nanographene-graphene heterostructures by engineering van der Waals interactions.

Combining strong light absorption and outstanding electrical conductivity, hybrid nanographene-graphene (NG-Gr) van der Waals heterostructures (vdWHs) represent an emerging material platform for versatile optoelectronic devices. Interfacial charge transfer (CT), a fundamental process whose full control remains limited, plays a paramount role in determining the final device performance. Here, we demonstrate that the interlayer vdW interactions can be engineered by tuning the sizes of bottom-up synthesized NGs to control the interfacial electronic coupling strength and, thus, the CT process in NG-Gr vdWHs. By increasing the dimensions of NGs from 42 to 96 sp2 carbon atoms in the polyaromatic core to enhance the interfacial coupling strength, we find that the CT efficiency and rate in NG-Gr vdWHs display a drastic increase of one order of magnitude, despite the fact that the interfacial energy driving the CT process is unfavorably reduced. Our results shed light on the CT mechanism and provide an effective knob to tune the electronic coupling at NG-Gr interfaces by controlling the size-dependent vdW interactions.

Polyaromatic cores for the exfoliation of popular 2D materials

Two-dimensional (2D) nanomaterials have attracted interest from the scientific community due to their unique properties. The production of these materials has been carried out by diverse methodologies, the liquid phase exfoliation being the most promising one due to its simplicity and potential scalability. The use of several stabilizers allows to obtain dispersions of these 2D nanomaterials in solvents with low boiling points. Herein we describe a general exfoliation method for different 2D materials employing a biphasic water/dichloromethane system and two different (poly)aromatic hydrocarbons (PAHs). This method allows us to obtain dispersions of the exfoliated 2D materials with high concentrations in the organic solvent. Due to the low boiling point of dichloromethane, and therefore its easy removal, the obtained dispersions can be employed as additives for different composites. We corroborate that the exfoliation efficiency is improved due to the π-π and van der Waals interactions between the PAHs and the layers of the 2D materials.

C-kit2 G-quadruplex stabilized via a covalent probe: exploring G-quartet asymmetry.

Several sequences forming G-quadruplex are highly conserved in regulatory regions of genomes of different organisms and affect various biological processes like gene expression. Diverse G-quadruplex properties can be modulated via their interaction with small polyaromatic molecules such as pyrene. To investigate how pyrene interacts with G-rich DNAs, we incorporated deoxyuridine nucleotide(s) with a covalently attached pyrene moiety (Upy) into a model system that forms parallel G-quadruplex structures. We individually substituted terminal positions and positions in the pentaloop of the c-kit2 sequence originating from the KIT proto-oncogene with Upy and performed a detailed NMR structural study accompanied with molecular dynamic simulations. Our results showed that incorporation into the pentaloop leads to structural polymorphism and in some cases also thermal destabilization. In contrast, terminal positions were found to cause a substantial thermodynamic stabilization while preserving topology of the parent c-kit2 G-quadruplex. Thermodynamic stabilization results from π–π stacking between the polyaromatic core of the pyrene moiety and guanine nucleotides of outer G-quartets. Thanks to the prevalent overall conformation, our structures mimic the G-quadruplex found in human KIT proto-oncogene and could potentially have antiproliferative effects on cancer cells.

An Aromatic Micelle‐Based Saccharide Cluster with Changeable Fluorescent Color and its Protein Interactions

AbstractTo develop a new type of synthetic saccharide clusters with changeable fluorescent colors, we herein designed a multisaccharide‐coated aromatic micelle. The new cluster forms in water through the quantitative assembly of bent polyaromatic amphiphiles bearing three mannose groups. The spherical assembly, with a 2 nm‐sized polyaromatic core and ca. 18 saccharide pendants, is stable even under high dilution conditions (up to 0.02 mM). The emission intensity and color of the saccharide cluster can be altered from moderate blue (ΦF=19 %) to strong red, orange, and green (ΦF up to 67 %) upon encapsulation of hydrophobic fluorescent dyes in water. Moreover, the present fluorescent clusters, both with and without the dyes, display selective interactions with mannose‐binding proteins in vitro.

Photolytic fate of (E)- and (Z)-endoxifen in water and treated wastewater exposed to sunlight

Endoxifen is the main active metabolite of a common cytostatic drug, tamoxifen. Endoxifen has been recently detected in the final effluent of municipal wastewater treatment plants. The antiestrogenic activity of endoxifen could bring negative effects to aquatic life if released to the water environment. This study elucidated the fate and susceptibility of (E)- and (Z)-endoxifen (2 μg mL−1, 1:1 wt ratio between the two easily interchangeable isomers) in wastewater and receiving surface water to sunlight. Phototransformation by-products (PBPs) and their toxicity were determined. Sunlight reduced at least 83% of endoxifen concentration in wastewater samples, whereas in surface water samples, 60% of endoxifen was photodegraded after 180 min of the irradiation. In ultrapure water samples spiked with endoxifen, PBPs were mainly generated via con-rotatory 6π-photocyclization, followed by oxidative aromatization. These PBPs underwent secondary reactions leading to a series of PBPs with different molecular weights. Eight PBPs were identified and the toxicity analysis via the Toxicity Estimation Software Tool revealed that seven of these PBPs are more toxic than endoxifen itself. This is likely due to the formation of poly-aromatic core in the PBPs due to exposure to sunlight. Therefore, highly toxic PBPs may be generated if endoxifen is present in water and wastewater exposed to sunlight. The presence, fates and activities of these PBPs in surface water especially at locations close to treated wastewater discharge points should be investigated.

Liquid Organic Frameworks: A Liquid Crystalline 8-Connected Network with Body-Centered Cubic Symmetry.

Liquid state self‐assembly is important for the understanding of the complex structures developed in abiogenesis and biogenesis as well as for numerous potential technological applications. Herein we report the first body‐centered cubic liquid crystalline phase with 8‐connected network topology and open octahedral network structure. It is formed by dynamic soft self‐assembly of X‐shaped polyphiles with oligo(para‐phenylene‐ethynylene) cores. The π‐conjugated rods with perfluorinated inner benzene rings form networks conjoined by eight‐way junctions, which are formed by nano‐segregated spheres involving hydrogen‐bonded polar end groups, while the branched aliphatic chains at opposite sides of the cores fill the continuum. This novel cubic phase is based on the I‐WP minimal surface separating the frameworks of polyaromatic cores from the most disordered chain segments. It can also be considered as a dense sphere packing. Such liquid organic frameworks, representing hybrids of sphere packings and networks could be of interest for organic photonics and other technologies.

Liquid Organic Frameworks: A Liquid Crystalline 8‐Connected Network with Body‐Centered Cubic Symmetry

AbstractLiquid state self‐assembly is important for the understanding of the complex structures developed in abiogenesis and biogenesis as well as for numerous potential technological applications. Herein we report the first body‐centered cubic liquid crystalline phase with 8‐connected network topology and open octahedral network structure. It is formed by dynamic soft self‐assembly of X‐shaped polyphiles with oligo(para‐phenylene‐ethynylene) cores. The π‐conjugated rods with perfluorinated inner benzene rings form networks conjoined by eight‐way junctions, which are formed by nano‐segregated spheres involving hydrogen‐bonded polar end groups, while the branched aliphatic chains at opposite sides of the cores fill the continuum. This novel cubic phase is based on the I‐WP minimal surface separating the frameworks of polyaromatic cores from the most disordered chain segments. It can also be considered as a dense sphere packing. Such liquid organic frameworks, representing hybrids of sphere packings and networks could be of interest for organic photonics and other technologies.

Molecular simulation of folding and aggregation of multi-core polycyclic aromatic compounds

Compared with polycyclic aromatic compounds (PACs) that have a single polyaromatic core, those having multiple cores connected by aliphatic chains can undergo significant internal conformational change, leading to folding, the stacking between the cores within the same molecule. In this work, we investigated this interesting phenomenon using molecular dynamics simulations, performed in three different solvents: water, heptane and toluene. In addition, by having several multi-core PACs in the same solution, the relationship between intramolecular folding and intermolecular aggregation was elucidated. In water, a single multi-core PAC preferred to stay in the unfolded state; contrarily, folded configuration became dominant when multiple molecules aggregated. In heptane and toluene, a multi-core PAC molecule could switch easily between folded and unfolded configurations, regardless of whether it was in single dispersed or aggregated states. Introduction of single-core PACs further modified the folding characteristics of multi-core PACs in water and heptane. This work provided fundamental insights into the interplay between folding, homoaggregation (between multi-core PACs) and heteroaggregation (between multi-core and single-core PACs) in a colloidal system.

Toward Predictive Molecular Dynamics Simulations of Asphaltenes in Toluene and Heptane.

The conventional definition of asphaltenes is based on their solubility in toluene and their insolubility in heptane. We have utilized this definition to study the influence of partial charge parametrization on the aggregation behavior of asphaltenes using classical atomistic molecular dynamics simulations performed on the microsecond time scale. Under consideration here are toluene- and heptane-based systems with different partial charges parametrized using the general AMBER force field (GAFF). Systems with standard GAFF partial charges calculated by the AM1-BCC and HF/6-31G*(RESP) methods were simulated alongside systems without partial charges. The partial charges implemented differ in terms of the resulting electrical negativity of the asphaltene polyaromatic core, with the AM1-BCC method giving the greatest magnitude of the total core charge. Based on our analysis of the molecular relaxation and orientation, and on the aggregation behavior of asphaltenes in toluene and heptane, we proposed to use the partial charges obtained by the AM1-BCC method for the study of asphaltene aggregates. A good agreement with available experimental data was observed on the sizes of the aggregates, their fractal dimensions, and the solvent entrainment for the model asphaltenes in toluene and heptane. From the results obtained, we conclude that for a better predictive ability, simulation parameters must be carefully chosen, with particular attention paid to the partial charges owing to their influence on the electrical negativity of the asphaltene core and on the asphaltenes aggregation.

Reversible aggregation of particles with short oligomeric sidechains at the surface studied with Langevin dynamics

We investigate nanoscopic aggregation of asphaltene nanoaggregates by means of Brownian dynamics simulations. Nanoaggregates that represent clusters of 6–10 asphaltene molecules are modelled as spherical particles with an attractive core consisting of polyaromatic hydrocarbons rings and short aliphatic tails that protrude from the surface, as in a spherical brush. As two such nanoaggregates approach each other, the steric repulsion that arises from interactions between the tails, is modelled using Alexander-de Gennes theory and Derjaguin approximation, while the attraction upon contact between polyaromatic cores, caused by van der Waals and other interactions is modelled as a Morse potential. The aggregation occurs when the steric barrier is overcome and the cores come into contact. Our simulations show that, with shallow interaction potentials, that is, with weak attractions and low barriers, the nanoaggregates form small agglomerates with ramified structure that are in metastable equilibrium with uniform solutions. These agglomerates can be described with a fractal dimensions below 1.5, which may represent soluble asphaltenes. The increase in attraction strength promotes aggregation and destabilizes the systems as in the case of dilution with a flocculant, for which several aggregation regimes are observed. Increasing the well-depth and/or barrier for nanoaggregate interaction leads to classical diffusion limited and reaction limited regimes. We find that with high barrier the clusters formed are less close-packed, and may represent the weak gel state typical for bitumen gel.

Genotoxic activity of 1,2,3-triazolyl modified furocoumarins and 2,3-dihydrofurocoumarins.

The furocoumarin backbone is a promising platform for chemical modifications aimed at creating new pharmaceutical agents. However, the high level of biological activity of furocoumarins is associated with a number of negative effects. For example, some of the naturally occurring ones and their derivatives can show genotoxic and mutagenic properties as a result of their forming crosslinks with DNA molecules. Therefore, a particularly important area for the chemical modification of natural furocoumarins is to reduce the negative aspects of their bioactivity. By studying a group of 21 compounds-1,2,3-triazolyl modified derivatives of furocoumarin and peucedanin-using the SOS chromotest, the Ames test, and DNA-comet assays, we revealed modifications that can neutralize the structure's genotoxic properties. Theoretical aspects of the interaction of the compound library were studied using molecular modeling and this identified the leading role of the polyaromatic molecular core that takes part in stacking-interactions with the pi-systems of the nitrogenous bases of DNA.