Heteroatom Substitution Research Articles

Improving the Photovoltaic Performance of Dithienobenzodithiophene-Based Polymers via Addition of an Additional Eluent in the Soxhlet Extraction Process.

Dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophene (DTBDT) is a kind of pentacyclic aromatic electron-donating unit with unique optoelectronic properties, but it has received less attention in the design of photovoltaic polymers. In this work, we copolymerized DTBDT with the electron-deficient unit of dithieno[3',2':3,4;2″,3″:5,6]benzo[1,2-c][1,2,5]thiadiazole (DTBT) and obtained two polymers, PE55 and PE56, with a synergistic heteroatom substitution strategy. When blended with the classic nonfullerene acceptor Y6, PE55 and PE56 achieve power conversion efficiencies (PCEs) of 13.78% and 14.49%, respectively, which indicates that the introduction of sulfur atoms on the conjugated side chain of the D unit is a promising method to enhance the performance of DTBDT-based polymers. Besides, we utilize dichloromethane and chloroform to separate the low molecular weight (Mw) fractions in the solvent extraction process to obtain PE55-CF and PE56-CB, and the PCEs are further improved to 15.00% and 16.11%, respectively. The stronger π-π stacking, optimized blend film morphology, and higher charge mobilities contribute to the enhanced PCEs for polymers with higher Mw obtained via the multistep solvent extraction strategy. Our results not only provide a simple and effective way to improve the photovoltaic performance of conjugated polymers but also imply that some reported polymers purified from the traditional one-step solvent extraction method might be seriously underestimated.

Molecular electron doping to single-walled carbon nanotubes and molybdenum disulfide monolayers

Carrier doping is an essential way to inject holes and electrons to electronic materials, which modulates their transport properties. While the substitution of heteroatoms essentially modulates the band structure of most semiconducting materials, chemical (molecular) doping can achieve relatively reliable carrier concentration modulation, particularly for nanocarbons and two-dimensional semiconductors. Compared to p-type counterparts, the stabilization of n-type carbon materials has been a challenge not only for basic science but also for various electronic device applications. This Mini-Review describes rational concepts for, and the results of, a stable n-type doping technique mainly for carbon nanotubes using molecular reactions and interactions. The stable n-type carbon nanotubes with controlled carrier concentration are implemented in complementary circuits and thermoelectric energy harvesters. The molecular and supramolecular n-type doping is not limited for carbon nanotubes, but is utilized in the fabrication of conducting transition metal dichalcogenides such as a molybdenum disulphide (MoS2) monolayer.

Dual functionalized Ni substitution in shuttle-like In2O3 enabling high sensitivity NH3 detection

Hetero-atom doping is an effective way to improve the sensing performance of metal oxide semiconductor gas sensors. However, the synergistic effects generated from hetero-atom substitution in In2O3 lattice and the relationship between the fine surface structure and sensing performance is still ambiguous. Here, Ni substitution in shuttle-like In2O3 nanoparticles have been successfully synthesized, and the materials are fabricated as gas sensor to detect ammonia, which is a toxic molecule that is harmful for human healthy. We find the 2 wt% Ni-doped In2O3 NPs exhibit high sensitivity (Ra/Rg = 2569.42 towards 50 ppm NH3 at 140 °C), achieving 34 folds improvement compared with pristine In2O3 NPs. The sensor also shows good long-term stability, high selectivity and fast response/recovery (23/10 s). Detail structural analysis illustrate the substitution of Ni in rh-In2O3 phase and surface O−(ad) species neighboring the substitution sites are recognized as the active sites, and the reactive oxygen species and surface Bronster acidity can be dramatically enhanced after Ni modification, which contribute to the improvement of sensing performance. Our work illustrate the synergistic effects of hetero-atom doping on the sensing performance and pave the way for design of high performance sensing materials.

Phenyl- and naphthyl-type heteroatom substitution blocks in naphthylene-[formula omitted]: A DFT study

Two-dimensional naphthylene-γ is a recently proposed carbon allotrope based on the concatenation of phenyl- and naphthyl-like blocks through tetragonal rings. This system is a narrow-gap semiconductor, which is also suitable to be cast into a boron-nitride configuration since it is a bipartite structure featuring only even-membered rings. It turns out BN configurations of naphthylene-γ can potentially result in systems suitable to be embedded into nanoelectronics applications, since they are expected to exhibit robust band gaps. With this motivation, we investigate the electronic properties of several hybrid systems hypothetically obtained by replacing part of naphthylene-γ’s C atoms by BN sectors with different concentrations. Our first principles simulations are based on density functional theory and show that the energy gap for these systems does not vary monotonically with increasing BN concentration. In fact, strategical choices for the sites undergoing C-to-BN substitution result in specific modifications in the electronic signature of the systems. We also investigated full-BN naphthylene-γ sheets which show band gaps significantly different from those of hexagonal-BN. We further investigated nanoribbons based on these BN sheets, showing that they closely follow the properties of their parent 2D structure, as they feature frontier states internally located over the ribbon structures.

Single Atom Selenium Substitution‐Mediated P‐Type Doping in Polythiophenes toward High‐Performance Organic Electronics and Thermoelectrics

AbstractHeavy heteroatom substitution of the backbone is an effective strategy to improve molecular packing and charge delocalization in polymer semiconductors. Such a backbone modification also facilitates oxidative doping as a result of reduced ionization potential (IP). Here, the effect of single‐atom selenium substitution on doping and charge transport properties of a class of polythiophene copolymers is explored. The room temperature (RT) conductivities of the doped polymers are significantly enhanced by the selenium substitution for both molecular doping and ion exchange doping. The enhanced conduction is rationalized by the better crystallinity of the selenium‐containing system, which can be reinforced by a chain‐extended ribbon‐phase morphology induced by thermal annealing, which is robust toward doping. The resulting increase in the charge delocalization of the doped selenium‐containing system is evidenced by temperature‐dependent conductivities. In ion exchange doped films the maximum conductivity of ≈700 S cm−1 and a high thermoelectric (TE) power factor (PF) of 46.5 μW m−1 K−2 is achieved for the doped selenophene polymer and signatures of a metal‐insulator (M–I) transition are observed that are characteristics for heterogeneous conduction systems. The results show that single‐atom selenium substitution is an effective molecular design approach for improving the charge transport and TE properties of conjugated polymers.

Band gap modulation of penta-BCN through different ways

The electronic structures of a series of penta-BCN monolayers with point-defect, compression and tensile strains, and heteroatom substitution were investigated by the first principle calculations. It was found that the ±10% biaxial strains on penta-BCN monolayer lead to a change in band gap from 2.65–3.37 eV. The B and N point-defects open the magnetism and a significant decrease in band gap of penta-BCN monolayer. The influences of heteroatoms on band gap of penta-BCN were also studied. It was shown that the substitution of Al and Ga lead to a significant decrease in band gap. Our study indicates that the band gap of penta-BCN can be efficiently modulated through different ways, which will expand the application of penta-BCN in photoelectric and photovoltaic fields.

Insighting the systematic impact of shape, size and substitution of heteroatoms in quinoidal oligomers to tune their optoelectronic properties

Insighting the systematic impact of shape, size and substitution of heteroatoms in quinoidal oligomers to tune their optoelectronic properties

Heteroatom-Substituted P2-Na2/3Ni1/4Mg1/12Mn2/3O2 Cathode with {010} Exposing Facets Boost Anionic Activity and High-Rate Performance for Na-Ion Batteries.

As an attractive cathode candidate for sodium-ion batteries, P2-type Na2/3Ni1/3Mn2/3O2 is famous for its high stability in humid air, attractive capacity, and high operating voltage. However, the low Na+ transport kinetics, oxygen-redox reactions, and irreversible structural evolution at high-voltage areas hinder its practical application. Herein, a comprehensive study of a microbar P2-type Ni2/3Ni1/4Mg1/12Mn2/3O2 material with {010} facets is presented, which exhibits high reversibility of structural evolution and anionic redox activity, leading to outstanding rate capability and cyclability. The notable rate performance (53 mA h g-1 at 20 C, 2.0-4.3 V) contributed to the high exposure of {010} facets via controlling the growth orientation of the precursor, which is certified by density functional theory calculation and lattice structural analysis. Mg substitution strengthens the reversibility of anionic oxygen redox and structural evolution in high-voltage areas that was confirmed by the in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy tests, leading to outstanding cyclic reversibility (68.9% after 1000 cycles at 5 C) and slowing down the voltage fading. This work provides new insights into constructing electrochemically active planes combined with heteroatom substitution to improve the Na+ transport kinetics and structural stability of layered oxide cathodes for sodium storage.

Spectroscopic and Computational Characterization of 2-Aza-1,3-butadiene, a Molecule of Astrochemical Significance.

Being N-substituted unsaturated species, azabutadienes are molecules of potential relevance in astrochemistry, ranging from the interstellar medium to Titan’s atmosphere. 2-Azabutadiene and butadiene share a similar conjugated π system, thus allowing investigation of the effects of heteroatom substitution. More interestingly, 2-azabutadiene can be used to proxy the abundance of interstellar butadiene. To enable future astronomical searches, the rotational spectrum of 2-azabutadiene has been investigated up to 330 GHz. The experimental work has been supported and guided by accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the two possible forms, trans and gauche. The trans species, more stable by about 7 kJ/mol than gauche-2-azabutadiene, has been experimentally observed, and its rotational and centrifugal distortion constants have been obtained with remarkable accuracy, while theoretical estimates of the spectroscopic parameters are reported for gauche-2-azabutadiene.

Catalytic oxidative desulfurization of light gas oil over Keggin-type phosphomolybdic acid supported on TUD-1 metallosilicates

A facile one-pot synthesis was developed to produce a series of metal-substituted TUD-1 mesoporous (MTUD-1) supports. The synthesized supports, with nominal Si/M molar ratio of 40 (where M = Al, Zr, Fe, Cu, or Ce), were impregnated with 20 wt% heteropoly phosphomolybdic acid (HPMo) and applied for the catalytic oxidation desulfurization of light gas oil (LGO). Physicochemical properties of the supports and catalysts were characterized using techniques such as N2-sorption, TPD-NH3, FT-IR, XRD, XPS, and XANES. Powder XRD analyses of the catalysts confirmed the highly dispersed Mo Keggin ion particles on metal substituted TUD-1 supports that that of pristine TUD-1 support. The substitution of heteroatoms in the TUD-1 matrix was verified by FTIR and XPS. The heterogenized molybdenum heteropoly acid was found to retain its Keggin structure on TUD-1 supports. Catalytic oxidation desulfurization performances of the catalysts were evaluated with LGO in a stirred tank batch reactor. Among the catalysts, cerium substituted TUD-1 supported catalyst showed the highest oxidation activity to sulfur compounds of LGO. The oxidation activity of HPMo/CeTUD-1catalyst was optimized by varying the process conditions. Besides a catalyst, ODS of LGO required an oxidant. The efficiency of oxidants for ODS of LGO over HPMo/CeTUD-1 followed the order: cumene hydroperoxide > tert-butyl hydroperoxide > hydrogen peroxide > molecular oxygen. The ODS activity of heterogenized molybdenum heteropoly acid is promoted by the Lewis acidity of CeTUD-1.

Influence of periodic heteroatom substitution in the aryl rings on optical properties and thermal stability of diarylethene derivatives

Photochromic diarylethene derivatives are one of the most promising candidates for various applications in optoelectronic devices. The heteroatom substitution of the aryl groups of diarylethene derivatives could greatly influence their optical properties and thermal stability. For example, the diarylethene derivatives with two thiophene rings (Dithienylethenes) have longer absorption wavelength, better fatigue resistance, sensitivity and thermal bistability than those with two furan rings. To further understand the influence of the heteroatom substitution in aryl rings, a series of diarylethene derivatives with different heteroatoms in IV (C, Si, Ge), V (N, P, As), and VI groups (O, S, Se) of Periodic Table were theoretically explored with DFT/TD-DFT functionals. According to the predicted results, the substituent effects of increasing atomic weights could influence the optical properties, the relative energies, the thermal bistability of the open isomer and the closed isomers. The maximum optical absorptions of the closed isomers and the open isomers could be finely tuned by these heteroatom groups in visible region of 395∼522 nm and in ultraviolet region of 300∼341 nm, respectively. The diarylethene with Se substituent diarylethene was predicted to have the best thermal bistability of all the nine substitutions and also have comparable photochomic properties than widely-used S diarylethene (Dithienylethenes). As 6π-electron system is indispensable part for nearly all known diarylethene derivates, the study probably provides a useful guideline for the future design of novel Se substituent diarylethene compounds with tunable photochromic properties and improved thermal bistability.

Structural and Electronic Properties of Boranes Containing Boron-Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline-2-imine Ligands.

The stabilization of elusive monomeric species containing multiple boron-chalcogen bonds has motivated the investigation of sophisticated ligand systems in the past few years. Recently, a series of neutral, Lewis acid-free chalcogenboranes were prepared by incorporation of an amido imidazoline-2-imine as the supporting ligand (Frank et al., Angew. Chem. Int. Ed. 2021, 60, 4633), resulting in well-defined molecular entities with pronounced multiple bond character, B=X (X=O, S, Se, Te). In view of the potential use of N-heterocyclic boranes (NHB=X) as ligands in catalysis and fine chemistry, we evaluated in this work the bonding properties of the new B=X compounds based on a π-backdonation model. The electronic properties of systems in question were modulated via systematic modifications of the NHB ring with respect to ligand variation, saturation, size, and heteroatom substitutions. Investigations into the B=X bond length and order, calculated by means of density functional theory methods, reveal enhanced B=X bonding properties for NHB rings with high electron delocalization in the NHB ring and bearing electron-withdrawing substituents; a fact that was also confirmed by computational assessment of electron interactions of the B=X species with a dicarbonyl manganese complex. We expect that the analysis will contribute to the rational optimization of existing ligands as well as the development of new moieties, which would further allow for exploration of new boron chemistry.

On-surface synthesis and characterization of nitrogen-substituted undecacenes

Heteroatom substitution in acenes allows tailoring of their remarkable electronic properties, expected to include spin-polarization and magnetism for larger members of the acene family. Here, we present a strategy for the on-surface synthesis of three undecacene analogs substituted with four nitrogen atoms on an Au(111) substrate, by employing specifically designed diethano-bridged precursors. A similarly designed precursor is used to synthesize the pristine undecacene molecule. By comparing experimental features of scanning probe microscopy with ab initio simulations, we demonstrate that the ground state of the synthesized tetraazaundecacene has considerable open-shell character on Au(111). Additionally, we demonstrate that the electronegative nitrogen atoms induce a considerable shift in energy level alignment compared to the pristine undecacene, and that the introduction of hydro-aza groups causes local anti-aromaticity in the synthesized compounds. Our work provides access to the precise fabrication of nitrogen-substituted acenes and their analogs, potential building-blocks of organic electronics and spintronics, and a rich playground to explore π-electron correlation.

How the Cobalt Position in the Keggin Anion Impacts the Activity of Tungstate Catalysts in the Furfural Acetalization with Alkyl Alcohols

AbstractKeggin heteropolyacids (HPAs) comprise a class of versatile catalysts, which have properties that can be easily adjusted through modification in their structure, such as the protons exchange, the removal or one or more MO unity (i. e., W or Mo) followed by doping with transition metals, or even less frequently, the substitution of heteroatom (i. e., P or Si). In this work, these effects were assessed by modifying the structure of silicotungstic acid (i. e., H4SiW12O40) with Co2+ cations. A series of Cobalt‐polyoxometalates (i. e., Co2SiW12O40, K6CoW12O40, K8SiW11O39, K6SiCoW11O39, K8CoW11CoO39) were synthesized and catalytically evaluated in furfural acetalization with alkyl alcohols. Spectroscopy analyses (i. e., UV‐Vis, FT‐IR, EDS), powder X‐ray diffraction patterns, scan electronic microscopy images, surface area, porosity, and thermal analyses provided the main physicochemical properties of the synthesized salts. Acidity properties were assessed by potentiometric titration and adsorbed Py‐FT‐IR spectroscopy. The impact of temperature, nature, and catalyst loading, and type of alcohol were investigated. The K6CoW12O40 salt was the most active and selective catalyst. We paid special attention to correlating the catalyst activity with its composition and properties.

Fabrication of Isomorphously Substituted W-MFI Membrane with High Performance for Ethanol Separation from Water.

Isomorphous substitution of heteroatoms is an effective platform for finely tuning the pore chemistry, pore structure, and surface properties of the zeolite framework as catalysts or separation membranes. A continuous and compact isomorphously substituted tungsten (W)-MFI membrane was firstly developed on coarse α-Al2 O3 tube dip-coated with W-MFI seeds using hydrothermal secondary growth and pretreated synthesis solution. The synthesized W-MFI membrane is found to be ethanol permselective having a pervaporation based separation factor and flux of 69 and 2.50 kg/m2 h, respectively while exhibiting the highest separation index of 170 kg/m2 h for the separation of 5 wt% ethanol-water mixture among the reported heteroatoms substituted and α-Al2 O3 supported tubular MFI membranes. The isomorphous substitution of W improves the hydrophobicity and also plays a significant role for the enhanced separation performance.

Triggering anionic redox activity in Fe/Mn-based layered oxide for high-performance sodium-ion batteries

Among various sodium-ion cathode materials, Fe/Mn-based layered oxides stand out due to cost-effectiveness and relatively high theoretical specific capacity. However, further enhancement in capacity and improvement in cyclability are still needed to meet the requirements for practical applications in sodium-ion batteries. Herein, we report that ruthenium-doped Na0.67Fe0.5Mn0.5O2 can not only achieve high reversible capacity but also deliver superior cycling stability. Owing to the substitution of 4d ruthenium heteroatoms, the cathode exhibits promising electrochemical performance with a higher reversible specific capacity of 170 mA h g−1 at 0.2C between 2 and 4 V as well as a stable cycling performance with 82.2% capacity retention at 2C after 100 cycles compared to its pristine counterpart. Advanced structural characterization techniques combined with theoretical calculations unveil that the presence of ruthenium ions can trigger anionic redox activity, thus leading to harvesting of extra capacity. Moreover, ruthenium ions can also play an important role in stabilizing and improving the structural framework, resulting in prominent cyclability and excellent rate performance. Overall, the present work demonstrates that anionic redox activity could be triggered by integration of trace 4d element in Fe/Mn-based layered oxides and represents an effective strategy to develop high-performance sodium cathodes.

Rational design of a large Stokes shift xanthene-benzothiozolium dyad for probing cysteine in mitochondria.

Xanthene-modified cyanine dyes are considered to be an effective means to extend the emission wavelength and improve the photo-stability of cyanine dyes. However, the fluorophores obtained by this strategy generally have narrow Stokes shifts, which severely limits their application in biological imaging. Herein, a reasonable design strategy is adopted to provide an effective strategy to commendably improve the Stokes shift of xanthene-benzothiozolium fluorophores via the simultaneous expansion of a molecular π-conjugated system and heteroatomic substitution. Combined with density functional theory calculation guidance, the O atom is replaced with the S atom in the xanthene moiety and a π-conjugated benzene ring is introduced in the benzothiozolium moiety. Surprisingly, the results of the spectroscopic experiment showed that the fluorescence emission wavelength of PhCy-OH was extended to 803 nm, and the Stokes shift was improved to 68 nm. PhCy-Cys can effectively distinguish Cys from homocysteine (Hcy) and glutathione (GSH) with an extremely low detection limit of 0.166 μM. Importantly, PhCy-Cys has the ability to image endogenous Cys in mitochondria, providing the potential for exploring the specific function and mechanism of Cys in regulating oxidative stress in mitochondria.

Tuning the properties of truxene by successive substitution of nitrogen and sulphur heteroatoms: a DFT insight.

In this study, truxene, along with its nitrogen- and sulphur-substituted counterparts were investigated for their properties. The important characteristic properties of a potential conducting material such as HOMO-LUMO gap, electron affinity, ionization potential, and density of states were calculated and compared for analysis. Furthermore, Fukui function and dual descriptor analyses were also carried out, to identify the reactive sites in each of the molecules, as well as understand the effect of substituted heteroatoms. It was seen that the di-substituted candidates were convincingly better fitting for optoelectronic applications.

Does boron or nitrogen substitution affect hydrogen physisorption on open carbon surfaces?

Incorporation of heteroatoms in carbon materials is commonly expected to influence their physical or chemical properties. However, contrary to previous results for methane adsorption, no technologically significant effect was identified for the hydrogen physisorption energies (measured 4.1-4.6 kJ mol-1 and calculated qst = -ΔHads = 4.1 ± 0.7 kJ mol-1 using a comprehensive set of levels of theory) as a function of B- and N-substitution of a mid-plane C-site on open carbon surfaces.

Multiple heteroatom substitution effect on destructive quantum interference in tripodal single-molecule junctions.

Quantum interference (QI) has been identified as a promising strategy for designing molecular-scale electronic devices. Heteroatom doping can effectively tailor the local structures and electronic states of intrinsic molecules, and endow them with modified electron transport properties. Herein, the impacts of multiple heteroatom substitution on destructive quantum interference (DQI) have been investigated based on tripodal meta-linked phenyl derivatives. Orbital views based on the Hückel method qualitatively predict the meta-anchored molecules with DQI features, while the introduction of nitrogen atoms can alleviate the suppression of DQI at the Fermi level (EF). This is generally consistent with the movement or even removal of the antiresonance dips in transmission spectra. The substituent on position 2 can raise the antiresonance energy, while the substituent on position 4 or 6 can lower the antiresonance energy. When more than one nitrogen atom is incorporated, the impact of the substitution on positions 4 and 6 can be superimposed and the substitution on positions 2 and 4 can be partly cancelled. The experimental single-molecule conductance for tripodal molecules follows the trend of 0N-3SMe < 1N-3SMe < 3N-3SMe < 2N-3SMe, in agreement with the theoretical prediction. Additionally, the regulation is the intrinsic property depending on the position and number of the nitrogen atoms in the backbone and is irrelevant to the number and type of the anchoring groups. Our findings provide qualitative guidance for tuning the electron transport based on DQI in heterocycle molecular devices.