Chalcogen Substitution Research Articles

Exploring novel Zn2SeX (X=S, Te) ternary chalcogenide: Studying the effect of chalcogen substitution on optoelectronic, and thermoelectric performance

Ternary-type semiconductor chalcogenide materials are distinguished by their outstanding thermal performance and tunable optoelectronic features. The electronic structure, optical, and transport features of novel Zn2SeX ternary (X=S, Te) semiconductors are investigated by employing the widely used density functional theory. Based on the band structure investigation, these materials were anticipated tohave a direct energy gap. The results demonstrated that direct energy losses were caused by the orbitals hybridization of S-p and the Se/Te-d in both materials. Compared to Zn2SeTe, Zn2SeS has a wider band gap at the Γ-point, meaning that electrons will have a lower effective mass and atoms possess a greater effective mass. The elements of the complex dielectric function and the significant optical properties were explored for potential use in optoelectronic applications. The unique peaks in I(ω) confirm extensive absorption in the UV range. They may be employed as very effective ultraviolet-reflecting materials based on the peaks in the reflection spectrum that have been observed. Since both materials positive Seebeck coefficient display p-type conductivity over the whole temperature range.

Investigating novel Mo2X3S (X = Se, Te) materials: probing the influence of chalcogen substitution on electronic, optical, and thermoelectric properties

The excellent thermal performance and adjustable optoelectronic characteristics distinguish the ternary semiconductors. Using the state-of-the-art density functional theory, the optoelectronic, and thermoelectric characteristics of new Mo2X3S (X = Se, Te) ternary chalcogenides are studied. The predicted band gap values with TB-mBJ for Mo2Se3S and Mo2Te3S materials were 1.41 eV and 2.10 eV, respectively. For their possible employment in optoelectronic applications, the components of the complex dielectric function and the vital optical characteristics were calculated and studied. For an increase in the band gap and with the replacement of Se to Te, the peaks in ε 1(ω) shifted to higher energies. Mo2Se3S and Mo2Te3S both show stronger absorption in the UV and visible ranges. Based on the observed peaks in the reflection spectrum, they may used as ultraviolet-reflecting materials with good efficacy. Both Mo2Se3S and Mo2Te3S have positive Seebeck coefficient values, they exhibit p-type conduction. The Mo2Te3S material displays a maximum Seebeck coefficient at about 500 K compared to Mo2Se3S, which leads to a maximum ZT.

Photoinduced dual bond rotation of a nitrogen-containing system realized by chalcogen substitution.

Photoinduced concerted multiple-bond rotation has been proposed in some biological systems. However, the observation of such phenomena in synthetic systems, in other words, the synthesis of molecules that undergo photoinduced multiple-bond rotation upon photoirradiation, has been a challenge in the photochemistry field. Here we describe a chalcogen-substituted benzamide system that exhibits photoinduced dual bond rotation in heteroatom-containing bonds. Introduction of the chalcogen substituent into a sterically hindered benzamide system provides sufficient kinetic stability and photosensitivity to enable the photoinduced concerted rotation. The presence of two different substituents on the phenyl ring in the thioamide derivative enables the generation of a pair of enantiomers and E/Z isomers. Using these four stereoisomers as indicators of which bonds are rotated, we monitor the photoinduced C-N/C-C concerted bond rotation in the thioamide derivative depending on external stimuli such as temperature and photoirradiation. Theoretical calculations provide insight on the mechanism of this selective photoinduced C-N/C-C concerted rotation.

First‐Principles Calculations to Investigate the Ground State, Mechanical Stability, Electronic Structure, and Optical Properties of Tl2SnX3 (X = S, Se, Te)

AbstractIn this work, the Density Functional Theory (DFT) analysis of the Tl2SnX3 series (X = S, Se, Te) is performed, and the ground states are confirmed by the calculation of the elastic constant Cij. Based on the DFT calculation, the Tl2SnX3 structures are direct‐gap semiconductors with bandgaps of 1.434, 1.181, and 0.907 eV, respectively. Chalcogen substitution significantly impacts their electronic structures, notably increasing the Density of States (DOS) width in the valence band from sulfur to tellurium, and shifting the dielectric function's real part, ε1(ω), toward lower energies. This change means that the optical activity and response to electric fields are better, with Tl2SnTe3 showing the best polarization response and light‐matter interaction abilities. Optical tests show that Tl2SnTe3 has very high optical absorption, peaking at ≈17 × 104 cm−1 along [010], and reflectivity levels above 90%, marking its suitability for high‐reflectivity applications. Moreover, loss energy function analysis also shows that Tl2SnTe3 has a strong electron loss resonance at lower energies, which means it has strong interactions with electrons.

Chalcogen atom effect on the intersystem crossing kinetic constant of oxygen- and sulfur disubstituted heteroporphyrins.

The modulation of the photophysical properties of di-substituted porphyrin rings upon the oxygen and sulfur-for-nitrogen replacement has been investigated at density functional theory (DFT) and its time-dependent formulation (TDDFT). The considered properties range from structural behaviors and excitation energies to spin-orbit coupling (SOC) and nonradiative intersystem kinetic constants. Results show that the SOC strongly increase upon chalcogen substitution and, accordingly, the computed nonradiative kinetic constant also indicate an efficient singlet-triplet intersystem crossing in the sulfur containing macrocycle. The presented results indicate an alternative way to properly modulate the porphyrin's crucial properties for their use in photodynamic therapy, without resorting to the use of heavy atoms.

Higher conductivity in doped ethylenedioxythiophene (EDOT) dimers with chalcogen-substituted end groups

Chalcogen substitution at the end groups of doped EDOT oligomers impacts on the crystal and electronic structures, enhancing their conducting properties.

Regulating the thermoelectric power factor of donor–acceptor copolymers by heavy chalcogen substitution: a first-principles study

Te substitution of sulfur (S) in PzDPP-based donor–acceptor copolymers enhances n-type power factor, while Se boosts both n-type and p-type power factors. Heavy chalcogen doping strategy shows promise for improving thermoelectric properties.

Enhancing the Chemical Stability and Photovoltaic Properties of Highly Efficient Nonfullerene Acceptors by Chalcogen Substitution: Insights from Quantum Chemical Calculations

Enhancing the Chemical Stability and Photovoltaic Properties of Highly Efficient Nonfullerene Acceptors by Chalcogen Substitution: Insights from Quantum Chemical Calculations

Heavy atom effect through chalcogen substitution in Red Nile dye: a theoretical investigation

Heavy atom effect through chalcogen substitution in Red Nile dye: a theoretical investigation

The impact of the chalcogen-substitution element and initial spectroscopic state on excited-state relaxation pathways in nucleobase photosensitizers: a combination of static and dynamic studies.

The substitution of oxygen with chalcogen in carbonyl group(s) of canonical nucleobases gives an impressive triplet generation, enabling their promising applications in medicine and other emerging techniques. The excited-state relaxation S2(ππ*) → S1(nπ*) → T1(ππ*) has been considered the preferred path for triplet generation in these nucleobase derivatives. Here, we demonstrate enhanced quantum efficiency of direct intersystem crossing from S2 to triplet manifold upon substitution with heavier chalcogen elements. The excited-state relaxation dynamics of sulfur/selenium substituted guanines in a vacuum is investigated using a combination of static quantum chemical calculations and on-the-fly excited-state molecular dynamics simulations. We find that in sulfur-substitution the S2 state predominantly decays to the S1 state, while upon selenium-substitution the S2 state deactivation leads to simultaneous population of the S1 and T2,3 states in the same time scale and multi-state quasi-degeneracy region S2/S1/T2,3. Interestingly, the ultrafast deactivation of the spectroscopic S3 state of both studied molecules to the S1 state occurs through a successive S3 → S2 → S1 path involving a multi-state quasi-degeneracy S3/S2/S1. The populated S1 and T2 states will cross the lowest triplet state, and the S1 → T intersystem crossing happens in a multi-state quasi-degeneracy region S1/T2,3/T1 and is accelerated by selenium-substitution. The present study reveals the influence of both the chalcogen substitution element and initial spectroscopic state on the excited-state relaxation mechanism of nucleobase photosensitizers and also highlights the important role of multi-state quasi-degeneracy in mediating the complex relaxation process. These theoretical results provide additional insights into the intrinsic photophysics of nucleobase-based photosensitizers and are helpful for designing novel photo-sensitizers for real applications.

Tuning the Emission Behaviour of Halogenated Bridged Ethers in Solution, as Solids and as Aggregates by Chalcogen Substitution

AbstractIn this contribution, we describe a set of three chlorinated bridged ethers with varying numbers of sulfur and oxygen atoms. The substitution leads to highly emissive compounds with tunable photophysical properties in relationship to their state of aggregation, i. e. in solution, as aggregates and in the solid state. Additionally, an in‐depth X‐ray diffractometric analysis supported by a Hirshfeld study of non‐covalent interactions and quantum chemical simulations was carried out. As the outcome, it was found that the content of sulfur in the compounds regulates the tuning of emission in solution as well as in the aggregated states as a consequence of their variation of planarity.

Controlling Spin-Orbit Coupling to Tailor Type-II Dirac Bands.

NiTe2, a type-II Dirac semimetal with a strongly tilted Dirac band, has been explored extensively to understand its intriguing topological properties. Here, using density functional theory calculations, we report that the strength of the spin-orbit coupling (SOC) in NiTe2 can be tuned by Se substitution. This results in negative shifts of the bulk Dirac point (BDP) while preserving the type-II Dirac band. Indeed, combined studies using scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy confirm that the BDP in the NiTe2-xSex alloy moves from +0.1 eV (NiTe2) to -0.3 eV (NiTeSe) depending on the Se concentrations, indicating the effective tunability of type-II Dirac Fermions. Our results demonstrate an approach to tailor the type-II Dirac band in NiTe2 by controlling the SOC strength via chalcogen substitution. This approach can be applicable to different types of topological materials.

Effects of different halogen and chalcogen substitutions on the ESIPT process of benzoxazole derivatives: Theoretical research

2-(2-carbomethoxy-3,4-dichloro-6-hydroxyphenyl)benzoxazole (DCl-O) has been extensively studied due to its excited-state intramolecular proton transfer (ESIPT) characteristics. To obtain molecules with better luminescence properties, eight derivatives were designed by using different atomic (S, Se and F, Cl) substitution for further study the influence of electronegativity on ESIPT properties. The ESIPT process and photophysical characters of DCl-O and derivatives were studied with theoretical methods. The analysis indicates that hydrogen bonds were strengthened upon photo-excitation. Moreover, the ESIPT reaction is more facile to proceed in derivatives with the weak electronegativity of substitution and the substitution of chalcogen has better effect than that of halogen.

Enhanced thermoelectric properties of polycrystalline CuCrS2−x Se x (x = 0, 0.5, 1.0, 1.5, 2) samples by replacing chalcogens and sintering

The optimization of thermoelectric properties of the CuCrSSe x (x = 0, 0.5, 1.0, 1.5, 2) samples was achieved by substitution in anionic sublattice and sintering at high temperature. The maximum power factor PF ∼ 0.3 mW (m·K)−2 among a series of samples with chalcogen substitution was obtained for CuCrS0.5Se1.5 sample at T = 300 K. The sintering made it possible to obtain the maximum value PF ∼ 2.1 mW (m·K)−2 for CuCrSe2 sample. This is due to a more than threefold increase in the thermopower S(T) in CuCrSe2 sample with a spin-orbital interaction in comparison with CuCrS0.5Se1.5 sample with the same optimal electrical conductivity σ ( 100 S cm−1), but without spin-orbital interaction. In CuCrSe2 sample, sintering effectively reduced the σ to an optimal value, suppressed of the magnetic phase transition in the range of 50–100 K, and the weak localization were replaced by weak antilocalization indicating the appearance of strong spin-orbit interaction below 20 K. As a result, an additional contribution to the S(T) appeared due to the filtration of current carriers caused by the strong spin-orbit interaction. The effect of grain boundaries on the properties σ and S(T) of the samples was investigated. It was established that polycrystalline samples with a high sulfur content were low-conductivity materials consisting of high-conductivity crystallites with the charge carriers concentration cm−3 separated by low-conductivity grain boundaries with fluctuation-induced tunneling conductivity. Both the replacement of sulfur with selenium and sintering led to a decrease in the energy barriers connecting grain boundaries. Selenium-dominated samples (CuCrS0.5Se1.5 and CuCrSe2) had high electrical conductivity with negligible energy barriers between grain boundaries. Logarithmic quantum corrections to the electrical conductivity was observed below 20 K, which indicated a quasi-two-dimensional electron transport in these samples.

Large-Size Superlattices Synthesized by Sequential Sulfur Substitution-Induced Transformation of Metastable MoTe2

We demonstrate a general protocol that uses a metastable phase as a template, followed by chalcogen substitution and phase transformation to obtain superlattices, or single crystals, of layered transition metal dichalcogenides (TMDs). In particular, the single-crystalline 2H-MoTe2 thin film, with the available wafer-scale synthesis, is selected as the template to study the chalcogen substitution mechanism. Analogous to the initiation polymerization process, a Te vacancy-initiated and S diffusion-mediated mechanism is proposed to describe the sequential substitution: the complete sulfurization of the top and bottom MoTe2 layers at the first stage, followed by the alloying process in the middle layers and finally the full conversion of the flake into MoS2. The substitution in each layer starts from the vacancy and expands to the nearby region catalyzed by the strain field, whereas the sulfurization sequence in the multilayer system is mediated by the cross-layer S diffusion process. This is confirmed by the cross-sectional observation of the intermediate state by scanning transmission electron microscopy and density functional theory studies. This unique mechanism enables us to fabricate the sub-centimeter scale, composition-tunable, and symmetric MoS2/MoTe2(1–x)S2x/MoS2 superlattices. Our work presents a new tool for the large-scale synthesis of TMD-based heterostructures toward industrial applications.

Breaking the out-of-plane symmetry of Janus WSSe bilayer with chalcogen substitution for enhanced photocatalytic overall water-splitting

Stacking the Janus transition metal dichalcogenides monolayer into bilayer is predicted to be a promising path to improve the photocatalytic water-splitting performance. However, the recovery of out-of-plane symmetry, caused by the energetically stacking pattern, makes the photocatalytic performance of bilayer disappointing. In this work, in order to break the out-of-plane symmetry, we choose selenium and tellurium to replace the surface sulphur of Janus WSSe bilayer, constructing the spatially asymmetric configurations. The first principles calculation results show that, the substitution strengthens the lightabsorptioncapacity, and promote the spatial separation of photogenerated carriers. Furthermore, the design of WSSe-WSeTe heterostructure, formed with tellurium substitution, improve the solar-to-hydrogen conversion efficiency and driving force of photo-induced carriers. Its solar-to-hydrogen conversion efficiency is up to 10.71%, and the photocatalytic water-splitting reactions on it could operate spontaneously, indicating an ideal water-splitting photocatalyst. Our study sheds light on a hopeful way to improve the photocatalytic performance for Janus transition metal dichalcogenides bilayers.

N-Type Organic and Polymeric Semiconductors Based on Bithiophene Imide Derivatives

ConspectusIn the last three decades, p-type (hole-transporting) organic and polymeric semiconductors have achieved great success in terms of materials diversity and device performance, while the development of n-type (electron-transporting) analogues greatly lags behind, which is limited by the scarcity of highly electron-deficient building blocks with compact geometry and good solubility. However, such n-type semiconductors are essential due to the existence of the p-n junction and a complementary metal oxide semiconductor (CMOS)-like circuit in organic electronic devices. Among various electron-deficient building blocks, imide-functionalized arenes, such as naphthalene diimide (NDI) and perylene diimide (PDI), have been proven to be the most promising ones for developing n-type organic and polymeric semiconductors. Nevertheless, phenyl-based NDI and PDI lead to sizable steric hindrance with neighboring (hetero)arenes and a high degree of backbone distortion in the resultant semiconductors, which greatly limits their microstructural ordering and charge transport. To attenuate the steric hindrance associated with NDI and PDI, a novel imide-functionalized heteroarene, bithiophene imide (BTI), was designed; however, the BTI-based semiconductors suffer from high-lying frontier molecular orbital (FMO) energy levels as a result of their electron-rich thiophene framework and monoimide group, which is detrimental to n-type performance.In this Account, we review a series of BTI derivatives developed via various strategies, including ring fusion, thiazole substitution, fluorination, cyanation, and chalcogen substitution, and elaborate the synthesis routes designed to overcome the synthesis challenges due to their high electron deficiency. After structural optimization, these BTI derivatives can not only retain the advantages of good solubility, a planar backbone, and small steric hindrance inherited from BTI but also have greatly suppressed FMO levels. These novel building blocks enable the construction of a great number of n-type organic and polymeric semiconductors, particularly acceptor-acceptor (or all-acceptor)-type polymers, with remarkable performance in various devices, including electron mobility (μe) of 3.71 cm2 V-1 s-1 in organic thin-film transistors (OTFTs), a power conversion efficiency (PCE) of 15.2% in all-polymer solar cells (all-PSCs), a PCE of 20.8% in inverted perovskite solar cells (PVSCs), electrical conductivity (σ) of 0.34 S cm-1 and a power factor (PF) of 1.52 μW m-1 K-2 in self-doped diradicals, and σ of 23.3 S cm-1 and a PF of ∼10 μW m-1 K-2 in molecularly n-doped polymers, all of which are among the best values in each type of device. The structure-property-device performance correlations of these n-type semiconductors are elucidated. The design strategy and synthesis of these novel BTI derivatives provide important information for developing highly electron-deficient building blocks with optimized physicochemical properties. Finally, we offer our insights into the further development of BTI derivatives and semiconductors built from them.

Stabilizing Hydrogen Adsorption through Theory-Guided Chalcogen Substitution in Chevrel-Phase Mo6X8 (X=S, Se, Te) Electrocatalysts.

In this work, we implement a facile microwave-assisted synthesis method to yield three binary Chevrel-Phase chalcogenides (Mo6X8; X = S, Se, Te) and investigate the effect of increasing chalcogen electronegativity on hydrogen evolution catalytic activity. Density functional theory predictions indicate that increasing chalcogen electronegativity in these materials will yield a favorable electronic structure for proton reduction. This is confirmed experimentally via X-ray absorption spectroscopy as well as traditional electrochemical analysis. We have identified that increasing the electronegativity of X in Mo6X8 increases the hydrogen adsorption strength owing to a favorable shift in the p-band position as well as an increase in the Lewis basicity of the chalcogen, thereby improving hydrogen evolution reaction energetics. We find that Mo6S8 exhibits the highest hydrogen evolution activity of the Mo6X8 series of catalysts, requiring an overpotential of 321 mV to achieve a current density of 10 mA cm-2ECSA, a Tafel slope of 74 mV per decade, and an exchange current density of 6.01 × 10-4 mA cm-2ECSA. Agreement between theory and experiment in this work indicates that the compositionally tunable Chevrel-Phase chalcogenide family is a promising framework for which electronic structure can be predictably modified to improve catalytic small-molecule reduction reactivity.

Electron Transfer in Rhodamine–TiO2 Complexes Studied as a Function of Chalcogen and Bridge Substitution

Many emerging light-harvesting systems for solar-energy capture depend on absorption of light by molecular dyes and subsequent electron transfer to metal-oxide semiconductors. However, the inhomoge...

First principles study of electronic and optical properties of copolymers PBDTX-BY (X, Y[dbnd]O, S, Se, Te)

Based on density functional theory (DFT) of first-principles, the electronic structure and optical properties of donor-acceptor (D-A) polymers Benzo[1,2-b:4,5-b'] Dithi-ophene-alt-benzo[c][1,2,5]thiadiazole (PBDT-BT) were investigated after the chalcogen replace at position X on the electron-rich donor (D) and position Y on the electron-deficient acceptor (A) separately. The results show that the substitution of position X has a significant effect on electronic structure. Firstly, the band gaps decrease with the chalcogen substitution in sequence mainly owing to the electronegativity. Then, the substitution of the O atom is beneficial to reduce the effective mass (m*) of the copolymer; when X = S, the charge transfer between the D and A units is significantly reduced. Relatively, the substitution on position Y has no obviously effected on their electron structure. Finally, Substitution of chalcogen at position X and Y affects the optical properties of the copolymers. The substitution on position X leads to the blue-shift of absorption peak, while the substitution on position Y shows an opposite situation.