Sulfur Substitution Research Articles

Disentangling the electron-lattice dichotomy of the excitonic insulating phase in Ta2Ni(Se1−xSx)5 with sulfur substitution and potassium deposition

Disentangling the electron-lattice dichotomy of the excitonic insulating phase in Ta2Ni(Se1−xSx)5 with sulfur substitution and potassium deposition

Regiodivergent Gold-Catalyzed Rearrangement-Addition Reactions of Sulfenylated Propargylic Carboxylates with Indoles.

Sulfenylated propargylic carboxylates were introduced to investigate the influence of sulfur substitution in gold-catalyzed alkyne activation pathways. Regiodivergent gold-catalyzed rearrangement and indole capture reactions proceed under mild conditions to give functionalized indole products bearing sulfenylated (Z)-enol carboxylate motifs. Pathways involving both 1,2- and 1,3-carboxylate migrations are achieved selectively, with indole being added in a 1,4 relationship to the sulfenyl group in each case. High levels of selectivity are influenced by the catalyst system, counterion, and carboxylate group.

Surface S doping induced ladder-regulation of lattice oxygen on the vertical FeCoOOH for water oxidation

Reasonable design and manipulation of appropriately activated lattice oxygen on the catalytic surface is key to efficient oxygen evolution reaction (OER). Utilizing anionic regulation mechanism, partial and rapid sulfur (S) substitution for oxygen can provide optimal surface reconstruction of CoFe oxo/(hydroxo)ide materials during the OER process. S-doping can modulate the local electronic structure of CoFe oxo/(hydroxo)ide compounds, thereby reducing the oxygen vacancies formation energy. This is the first gradient to form more oxygen vacancies, thus activating lattice oxygen. In addition, the hybridization between Co/Fe 3d and O 2p is enhanced by the trace S doping on the surface of CoFe oxo/(hydroxo)ides, suggesting a faster rate of electronic transfer. Therefore, the electrochemical measurements show that the obtained electrocatalyst demonstrates an overpotential of 361.1 mV at 100 mA cm−2 and long-term stability. The characterizations after stability tests confirm that surface S was rapidly leached to form a second gradient high concentration oxygen vacancies. Moreover, the formation of uniformly dispersed vertical nanoplate arrays of FeCoOOH exposes a wealth of active sites. This work provides a promising ladder regulation strategy of lattice oxygen for the design of pre-catalysts for the development of large-scale water decomposition systems.

Improvement in thermoelectric figure of merit of Bi2Se3 crystal with Sulfur substitution

Bismuth Selenide has gained a great deal of attention as a thermoelectric material owing to its lower toxicity compared to Bi2Te3 based materials. In this work, Sulfur substitution in Bi2Se3 is carried out by the vertical Bridgman method and the influence of Sulfur on the structural, electrical and thermal properties of Bi2Se3 was studied. The thermoelectric figure of merit (ZT) was calculated from electrical conductivity, Seebeck coefficient and thermal conductivity, which were measured from 303 K to 773 K. Sulfur incorporation did not improve the electrical conductivity of Bi2Se3 but proved to be beneficial in improving the Seebeck coefficient and reducing thermal conductivity. Hence, the calculated figure of merit of Bi2Se2.7S0.3 crystal comes out to be 0.72 at 543 K, which is higher than that of pure Bi2Se3 crystal, which is 0.31 at 533 K.

Thermoelectric performance of n-type Bi2S3-alloyed Bi2Te2.7Se0.3

The effect of isovalent sulfur substitution on the thermoelectric properties of n-type Bi2Te2.7Se0.3 alloy has been studied systematically. At low sulfur concentrations, where the samples are single phase, changes in defect chemistry and density of states impacted significantly electrical resistivity and thermopower. Isovalent sulfur substitution enhanced thermopower and reduced thermal conductivity for both single and multiphase samples. This reduction in thermal conductivity was particularly noticeable in samples containing Bi2S3-based secondary phase, reaching a low thermal conductivity of ∼0.3 W m−1 K−1 at 525 K. A maximum figure of merit, zT, of 0.55 was achieved for the sample with the highest sulfur content, demonstrating the potential of this approach to optimise the thermoelectric performance of Bi2Te3-based materials.

2D Reconfigurable van der Waals Heterojunction for Logic Gate Circuits and Wide-Spectrum Photodetectors via Sulfur Substitution and Band Matching.

The attractive physical properties of two-dimensional (2D) semiconductors in group IVA-VIA have been fully revealed in recent years. Combining them with 2D ambipolar materials to construct van der Waals heterojunctions (vdWHs) can offer tremendous opportunities for designing multifunctional electronic and optoelectronic devices, such as logic switching circuits, half-wave rectifiers, and broad-spectrum photodetectors. Here, an optimized SnSe0.75S0.25 is grown to design a SnSe0.75S0.25/MoTe2 vdWH for logic operation and wide-spectrum photodetection. Benefiting from the excellent gate modulation under the appropriate sulfur substitution and type-II band alignment, the device exhibits reconfigurable antiambipolar and ambipolar transfer behaviors at positive and negative source-drain voltage (Vds), enabling stable XNOR logic operation. It also features a gate-modulated positive and negative rectifying behavior with rectification ratios of 265:1 and 1:196, confirming its potential as half-wave logic rectifiers. Besides, the device can respond from visible to infrared wavelength up to 1400 nm. Under 635 nm illumination, the maximum responsivity of 1.16 A/W and response time of 657/500 μs are achieved at the Vds of -2 V. Furthermore, due to the strong in-plane anisotropic structure of SnSe0.75S0.25-alloyed nanosheet and narrow bandgap of 2H-MoTe2, it shows a broadband polarization-sensitive function with impressive photocurrent anisotropic ratios of 15.6 (635 nm), 7.0 (808 nm), and 3.7 (1310 nm). The direction along the maximum photocurrent can be reconfigurable depending on the wavelengths. These results indicate that our designed alloyed SnSe0.75S0.25/MoTe2 vdWH has reconfigurable logic operation and broadband photodetection capabilities in 2D multifunctional integrated circuits.

Impact of sulfur substitution on biotin binding affinity to streptavidin

In this study, we investigated how the replacement of the tetrahydrothiophene ring of biotin with either an oxolane or (methyl)pyrrolidine moiety may affect its molecular interactions, in an effort to identify alternative affinity ligands suitable for in vitro and in vivo applications in synthetic biology. Initial molecular dynamics (MD) simulations suggested the potential formation of a hydrogen bond between either the oxygen or nitrogen atom of the envisaged tetrahydroheteryl analogues and the Thr90 residue of streptavidin, mirroring the sulfur-centered hydrogen bond detected by the crystallographic analysis of the biotin-streptavidin interaction. Therefore, oxy-, aza-, and N-methylazabiotin were readily synthesized starting from chiral five- or six-carbon sugar precursors. Based on fluorescence-based titration experiments using the corresponding fluorescein conjugates, oxybiotin showed a binding behavior similar to biotin with streptavidin, while both amino analogues displayed lower binding capacities. Notably, azabiotin exhibited a pH-dependent interaction profile, demonstrating enhanced binding under acidic conditions but weaker binding under basic pH, which could be exploited for various purposes.

Thio and Seleno-Psoralens as Efficient Triplet Harvesting Photosensitizers for Photodynamic Therapy.

The Psoralen (Pso) molecule finds extensive applications in photo-chemotherapy, courtesy of its triplet state forming ability. Sulfur and selenium replacement of exocyclic carbonyl oxygen of organic chromophores foster efficient triplet harvesting with near unity triplet quantum yield. These triplet-forming photosensitizers are useful in Photodynamic Therapy (PDT) applications for selective apoptosis of cancer cells. In this work, we have critically assessed the effect of the sulfur and selenium substitution at the exocyclic carbonyl (TPso and SePso, respectively) and endocyclic oxygen positions of Psoralen. It resulted in a significant redshifted absorption spectrum to access the PDT therapeutic window with increased oscillator strength. The reduction in singlet-triplet energy gap and enhancement in the spin-orbit coupling values increase the number of intersystem crossing (ISC) pathways to the triplet manifold, which shortens the ISC lifetime from 10-5 s for Pso to 10-8 s for TPso and 10-9 s for SePso. The intramolecular photo-induced electron transfer process, a competitive pathway to ISC, is also considerably curbed by exocyclic functionalizations. In addition, a maximum of 115 GM of two-photon absorption (2PA) with IR absorption (660-1050 nm) confirms that the Psoralen skeleton can be effectively tweaked via single chalcogen atom replacement to design a suitable PDT photosensitizer.

Novel lithium ionic cocrystals with benzoic acid derivatives and L-proline: Synthesis, X-ray structures, IR spectrums, DSC analysis, and water solubility

Lithium therapy has been employed in the treatment of mental disorders for decades, while lithium cocrystals have garnered growing attention in recent years. However, research on lithium ionic cocrystals (ICCs) remains limited, and more research is needed for their structure diversities and interaction studies. Given this background, we synthesized six lithium ICCs with l-proline and benzoic acid derivatives, each substituted with different functional groups (-OH, -SH, -CH3, –OCH3, -SCH3) as co-formers. Their crystal structures were initially determined using single-crystal X-ray diffraction (SCXRD) and subsequently evaluated through infrared spectroscopy (IR), differential scanning calorimetry (DSC), and water solubility testing. Notably, we observed significant variations in the crystal packing, interaction mode, and physicochemical properties of the prepared ICCs, particularly in comparison between oxygen and sulfur substitution. IR spectra revealed signal shifts and intensity changes consistent with lithium coordination and other weak interactions involved. Moreover, all ICCs exhibited markedly enhanced thermal stabilities and water solubilities. In conclusion, our study not only yielded novel lithium ICCs but also provided valuable insights for the preparation of ICCs based on similar pharmacological templates.

A substitutional quantum defect in WS2 discovered by high-throughput computational screening and fabricated by site-selective STM manipulation

Point defects in two-dimensional materials are of key interest for quantum information science. However, the parameter space of possible defects is immense, making the identification of high-performance quantum defects very challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS2, which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur (CoS0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}_{{{{{{{{\\rm{S}}}}}}}}}^{0}$$\\end{document}) and fabricate it with scanning tunneling microscopy (STM). The CoS0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}_{{{{{{{{\\rm{S}}}}}}}}}^{0}$$\\end{document} electronic structure measured by STM agrees with first principles and showcases an attractive quantum defect. Our work shows how HT computational screening and nanoscale synthesis routes can be combined to design promising quantum defects.

Quasi-intrinsic thiobase derivatives as potential targeted photosensitizers in two-photon photodynamic therapy

In this study, a set of potential quasi-intrinsic photosensitizers for two-photon photodynamic therapy (PDT) are proposed based on the unnatural 2-amino-8-(1′-β-ᴅ-2′-deoxyribofuranosyl)-imidazo[1,2-ɑ]-1,3,5-triazin-4(8H)-one (P), which is paired with the 6-amino-5-nitro-3-(1′-β-ᴅ-2′-deoxyribofuranosyl)-2(1H)-pyridone (Z) and can specifically recognize breast and liver cancer cells. Herein, the effects of sulfur substitution and electron-donating/electron-withdrawing groups on the photophysical properties in aqueous solution are systematically investigated. The one- and two-photon absorption spectra evidence that the modifications could result in red-shifted absorption wavelength and large two-photon absorption cross-section, which contributes to selective excitation and provides effective PDT for deep-seated tissues. To ensure the efficient triplet state population, the singlet–triplet energy gaps and spin–orbit coupling constants were examined, which is responsible for a rapid intersystem crossing rate. Furthermore, these thiobase derivatives are characterized by the long-lived T1 state and the large energy gap for radiationless transition to ensure the generation of cytotoxic singlet oxygen.

Facile surfactant-free microwave-assisted solvothermal synthesis of Cu2Te1−xSx with enhanced thermoelectric performance

Cu2Te-based compounds show promise for thermoelectric applications, but their synthesis typically involves ball milling or melting-annealing processes. Here, we present a surfactant-free microwave-assisted solvothermal method for the controlled synthesis of Cu2Te1−xSx (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) nanostructures at 503 K within just 30 min. The substitution of sulfur promotes the formation of a hexagonal structure in Cu2Te1−xSx with x of 0.2 – 0.5, and inhibits phase transitions during heating. Moreover, the alloying of sulfur contributes to a reduction in hole concentrations toward the optimal range, resulting in enhanced power factors (e.g., 910 μW m−1 K−2 at 825 K for Cu2Te0.9S0.1) and reduced thermal conductivity (e.g., 0.53 W m−1 K−1 at 825 K for Cu2Te0.5S0.5). Ultimately, Cu2Te0.5S0.5 achieves a maximum dimensionless figure of merit of 0.80 at 825 K. This study offers a controllable solution-based strategy for synthesizing Cu2Te-based materials with tunable compositions and enhanced thermoelectric performance.

Oxysulfide perovskites: reduction of the electronic band gap of RbTaO3 by sulfur substitution

In this study, the effects of sulfur substitution on the structural, mechanical, electronic, optical, and thermodynamic properties of RbTaO3−x S x have been investigated using the WIEN2k code in the framework of density functional theory (DFT). The cubic phase of RbTaO3 transforms to tetragonal for RbTaO2S and RbTaOS2; the latter transforms again to a cubic phase with added sulfur for RbTaS3. The results show that substituting S for O anions in RbTaO3 effectively decreased the band gap [calculated using TB-mBJ functional] from 2.717 eV to 1.438 eV, 0.286 eV, and 0.103 eV for the RbTaO3, RbTaO2S, RbTaOS2, and RbTaS3 compounds, respectively. The optical constants such as dielectric constant, refractive index, absorption coefficient, photoconductivity, reflectivity, and loss function have been calculated and analyzed. The elastic constants and moduli and their anisotropic nature were also investigated. Finally, the Debye temperature, thermal conductivity, melting temperature, specific capacities, and thermal expansion coefficients were computed and analyzed using established formalisms. The reduced band gap (1.438 eV) and high absorption coefficient (∼106 cm−1) of RbTaO2S, make it suitable for solar cell applications and for other visible light devices. Both ordered structure and super-cell have been used to cross-check results for RbTaO2S and RbTaOS2 compositions.

Enhancing thermoelectric behavior of Bismuth Selenide crystal via substitution of Sulfur and Tellurium

Sulfur and Tellurium substituted Bismuth Selenide (Bi2Se3-x-ySxTey, x = y = 0, 0.1, 0.15, 0.2) quaternary alloy crystals were synthesized by using vertical Bridgman technique. Energy dispersive analysis of X-rays confirmed elemental composition and purity of the grown crystals. Field emission scanning electron microscopy showed that the growth of crystals has occurred by layer growth mechanism. Rhombohedral crystal structure is validated through analysis of powder X-ray diffraction pattern. Thermoelectric parameters such as electrical conductivity, Seebeck coefficient and thermal conductivity were calculated from 303 K to 773 K and from that power factor as well as figure of merit have been determined for all grown crystals. Electrical conductivity significantly increased due to Sulfur and Tellurium incorporation and maximum value obtained is 147.72 S/cm at 503 K for Bi2Se2.6S0.2Te0.2. Seebeck coefficient and thermal conductivity showed decrement with incorporation of Sulfur and Tellurium. Reduction in thermal conductivity and enhancement in electrical conductivity resulted in the improvement of figure of merit. Sulfur and Tellurium substitution showed considerable improvement in ZT from 0.31 (533 K) for pristine Bi2Se3 to 1.28 (523 K) for Bi2Se2.6S0.2Te0.2.

Exploring the Theoretical Foundations of Thermally Activated Delayed Fluorescence (TADF) Emission: A Comprehensive TD-DFT Study on Phenothiazine Systems.

This study conducts a thorough theoretical investigation of Thermally Activated Delayed Fluorescence (TADF) in phenothiazine-based systems, examining ten molecular configurations recognized experimentally as TADF-active. Employing Time-Dependent Density Functional Theory (TD-DFT), our analysis spans the investigation of singlet-triplet energy gaps (ΔEST), spin-orbit coupling, and excitation characteristics using Multiwfn. This approach not only validates the adherence to El Sayed's rule across these systems but also provides a detailed understanding of charge transfer dynamics, as visualized through heat maps. A significant aspect of our study is the exploration of different oxidation states of sulfur and site substitutions on phenothiazine. This systematic variation aims to identify additional TADF-active compounds, drawing parallels with properties characterizing other known TADF emitters. Our investigation into Reverse Intersystem Crossing (rISC) rates and the analysis of dihedral angles in relation to ΔEST values offer nuanced insights into the TADF behaviours of these molecules. By integrating rigorous computational analysis with practical implications, we provide a foundational understanding that enhances the design and optimization of phenothiazine-based materials for optoelectronic applications. This work not only advances our theoretical understanding of TADF in phenothiazine derivatives but also serves as a guide for experimentalists and industry professionals in the strategic design of new TADF materials.

Comparison of 2-Aminopyridine and 4-Thiopseudisocytosine PNA Nucleobases for Hoogsteen Recognition of Guanosine in RNA.

Peptide nucleic acid (PNA) is emerging as a promising ligand for triple-helical recognition of folded biologically relevant RNA. Chemical modifications are actively being developed to achieve high affinity and sequence specificity under physiological conditions. In this study, we compared two modified PNA nucleobases, 2-aminopyridine (M) and 4-thiopseudisocytosine (L), as alternatives to protonated cytosine (unfavorable under physiological conditions), to form more stable triplets than C+·G-C. Both nucleobases formed M+·G-C and L·G-C triplets of similar stability; however, the L-modified PNAs showed somewhat reduced sequence specificity. In conclusion, M and L represent two alternative solutions to the problem of cytosine protonation in triple-helical recognition of RNA. In M, the pKa is increased to favor partial protonation, which improves solubility and cellular uptake of M-modified PNAs. In L, the sulfur substitution enhances favorable hydrophobic interactions, which may have advantages in avoiding off-target effects that may be caused by cationic modifications. However, our results showed that substituting Ms with Ls did not restore the sequence specificity of a PNA containing cationic groups.

Band-Gap Engineering and Unusual Behavior of Electronic Properties during Anion Substitution of Sulfur in LaFSe

Band-Gap Engineering and Unusual Behavior of Electronic Properties during Anion Substitution of Sulfur in LaFSe

On surface synthesis of an eleven-ring sulfur-doped nonacene.

Dithienoacenes with a heptacene core, heptaceno[2,3-b:11,12-b']bis[1]benzothiophene, have been synthesized through the combination of solution and surface assisted chemistry. The atomic composition, structural arrangement and electronic properties of the molecules on the Au(111) surface have been deeply explored by non-contact atomic force microscopy (nc-AFM), bond-resolved scanning tunnelling microscopy (BR-STM) and scanning tunneling spectroscopy (STS) corroborated by density functional theory (DFT) calculations. Our combined experiments reveal modifications induced by sulfur substitution.

Sulfur substitution in Fe-MOF-74: implications for electrocatalytic CO2 and CO reduction from an ab initio perspective

Employing first-principles methods, we investigated the electrocatalytic reduction of CO2 and CO on two Fe-based MOFs: Fe2DOBDC and Fe2DSBDC.

Computational approach to enhance thermoelectric performance of Ag2Se by S and Te substitutions.

Designing an n-type thermoelectric material with a high thermoelectric figure of merit at near room temperature is extremely challenging. Generally, pristine Ag2Se reveals unusually low thermal conductivity along with a high electrical conductivity and Seebeck coefficient, which leads to high thermoelectric performance (n-type) at room temperature. Herein, we report a pseudo-ternary phase (Ag2Se0.5Te0.25S0.25) that exhibits significantly high thermoelectric performance (zT ∼ 2.1) even at 400 K. First-principles calculation reveals that the Rashba type of spin-dependent band spitting, which originates due to sulfur and tellurium substitution, helps to improve the thermopower magnitude. We also show that the intrinsic carrier mobility is not only controlled by the carrier effective mass but is substantially limited by longitudinal acoustic and optical phonon modes, which is an extension of the deformation potential theory. Locally off-center sulfur atoms, together with the increase in configurational entropy via substitution of Te and S atoms in Ag2Se, lead to a drastic reduction in the lattice thermal conductivity (klat ∼ 0.34 W m-1 K-1 at 400 K). The Rashba effect coupled with the configurational entropy synergistically results in a high thermoelectric figure of merit in the n-type thermoelectric material working in the near-room-temperature regime.