Charge Transition Research Articles

Unusual bi- and tetra-nuclear cobalt(II) bis(salamo)-based complex: Preparation, crystal structure and theoretical calculations and fluorescence properties

Two unusual bis(salamo)-based Co(II) complexes, [Co2(L)(OMe)]·2MeOH (1) and [Co4(L1)4(MeOH)4] (2) were designed and successfully prepared, and characterized structurally. The crystal structure analysis showed that complex 1 is composed of one fully deprotonated ligand (L)3− moity, two divalent Co(II) atoms and one bridge-coordinated methanol molecule, while complex 2 is an asymmetric homotetranuclear structure made up of four Co(II) atoms, four fully deprotonated (L1)2− units and four coordinated methanol molecules. It is noteworthy that the reaction of cobalt(II) nitrate with H3L produces complex 2. This complex is not obtained from the original ligand H3L but from a new ligand H2L1. Therefore, the phenomenon can be used to prepare metal(II/III) complexes with excellent structure. The molecular frontier orbitals HOMO and LUMO of H3L and complexes 1 and 2 were analyzed by DFT calculations, and the results showed that the energy gaps of the complexes were reduced due to the combination of the orbitals compared to the ligand. The reaction sites of H3L with Co(II) atoms were analyzed by ESP studies, and the results showed that the crystal structures of the complexes are consistent with the theoretical predictions. Hirshfeld surface analyses indicated the different interactions in the complexes, and revealed that the main contributions to the crystal stacking were from HH, CH and HO interactions. The interactions in the complexes were further explored by IRI research, the results exhibited that there are abundant interactions in complexes 1 and 2, which are important for their construction of supramolecules. The fluorescence strengths of complexes 1 and 2 are significantly lower compared to H3L, which can be attributed to the ligand to metal charge transition (LMCT).

Surface charge accumulation of post insulator: Dominant charge transition under different conditions

AbstractAn insulator surface charge may be responsible for flashover along the insulator surface. In this study, experimental investigations of post insulator surface charge are performed using a variety of voltage, gas type, and gas pressure conditions. Combining the model of surface charge transport, the dominant charge transition is revealed considering gas partial discharge. The results show that hetero‐polar charge accumulates near the high voltage electrodes on the insulator at one atmospheric pressure with an applied DC voltage ranging from −10 to −60 kV. The area ratio of the hetero‐polar charge increases from 23% to 53%. It also generates a reversed polarity of surface charges. Under −20 kV, the surface charge near the grounded electrode gradually becomes homo‐polar charges with the decrease of SF6 in 0.5 MPa SF6/N2 gas mixtures. In this case, the most dominant pathway for charge accumulation is through the insulation gas rather than the insulator. For the 20%SF6/80%N2 gas mixtures, homo‐polar charge speckles appear near the grounded plate electrode when the pressure of SF6/N2 gas mixtures decreases to 0.1 MPa. This means that the partial discharge occurs in gas side under a lower gas pressure. Refer to the presenting findings, the dominant charge transition on post insulators is provided as an important reference.

Band-gap reduction of oxides via partial hydrolysis-enhanced carbothermic reaction

In the realm of metal oxide semiconductors, reducing the bandgap often necessitates the cumbersome process of high-temperature annealing in a controlled atmosphere, such as through the carbothermal reaction. However, we unveil a graceful approach to crafting narrow-gap metal oxides by delicately governing the hydrolysis reaction of metal alkoxides. Through carefully modulated hydrolysis, carbon-based residues nestled within intermolecular confines transform into graphite, nestled beside the metal oxide. This metamorphosis enables the carbothermic reaction to transpire even in the open air at temperate conditions. Diving deeper, theoretical explorations illuminate that oxygen vacancies, introduced by partial hydrolysis, are the driving force behind the color transformation of the oxides and the enhancement of photothermal conversion efficiency. The method presented here, rooted in partial hydrolysis, paves a fresh path for the creation of black metal oxide with tailored charge transition behavior, holding great promise for solar photothermal applications.

Multifunctional-response Cd-LMOF based on triphenylamine with high selectivity for the detection of chromium ions

A luminescent Cd-MOF is synthesized based on a triphenylamine-core ligand tris(4-(1H-imidazol-1-yl)phenyl)amine (TIPA), [Cd2(TIPA)2(oba)2] n (LMOF-1, oba = 4,4′-oxybisbenzoic). Fluorescence analysis of LMOF-1 shows blue light which can be attributed to the double role of ligand-to-ligand charge transition (LLCT) and aggregation-induced emission (AIE) effect, indicating that it can be used as a potential LED phosphor. As a luminescent sensor, LMOF-1 has excellent performance in detecting Cr3+, CrO4 2−, and Cr2O7 2− in water. Significantly, the quenching coefficient (K SV) of Cr3+ is 1.64 × 104 M−1, which is greater than or comparable to those reported in the literature. Therefore, LMOF-1 may be an excellent multi-functional response and recyclable luminescent sensor.

P-Type Impurities in 4H-SiC Calculated Using Density Functional Theory

We have investigated the p-dopant potential of 14 different impurities (Be, B, F, Mg, Al,Ca, Sc, Cu, Zn, Ga, In, Ba, Pt, and Tl) within 4H-SiC via Density Functional Theory (DFT) calcu-lations using a hybrid density functional. We analyse the incorporation energies of impurity atomson Si and C sites as well as the character of lattice distortion induced by impurities. The calculatedthermal ionization energies confirm that Al and Ga on the Si site are the best candidates for p-dopingof 4H-SiC. Although we find some correlation of incorporation energies with atomic radii of impuri-ties, the difference in chemical interaction with neighbouring atoms and strong lattice distortions playimportant roles in determining the impurity incorporation energies and charge transition levels. Wefind Al to still be the best and most industrially viable p-dopant for 4H-SiC.

Design of a Double-Photoelectrode Sensing System with a Metal-Organic Framework-Based Antenna-like Strategy for Highly Sensitive Detection of PD-L1.

Currently, the construction of heterojunctions as a method to enhance photoelectrochemical (PEC) activity has shown prospective applications in the analytical field. Restricted by carrier separation at the interface, developing a heterojunction sensing platform with high sensitivity remains challenging. Here, a double-photoelectrode PEC sensing platform was fabricated based on an antenna-like strategy by integrating MIL-68(In)-NH2, a p-type metal-organic framework (MOF) photocatalyst, as a photocathode with the type-II heterojunction of CdSe/MgIn2S4 as a photoanode synchronously. According to the ligand-to-metal charge transition (LMCT), the photo-generated carriers of MIL-68(In)-NH2 transferred from the organic ligand to the metal cluster, which provides an efficient antenna-like transfer path for the charge at the heterojunction interface. In addition, the sufficient Fermi energy difference between the double photoelectrode provides the continuous internal driving force required for rapid carrier separation at the anode detection interface, significantly improving the photoelectric conversion efficiency. Hence, compared with the traditional heterojunction single electrode, the photocurrent response of the double-photoelectrode PEC sensing platform developed using the antenna-like strategy is 2.5 times stronger. Based on this strategy, we constructed a PEC biosensor for the detection of programed death-ligand 1 (PD-L1). The elaborated PD-L1 biosensor exhibited sensitive and precise detection capability with a detection range of 1 × 10-5 to 1 × 103 ng/mL and a lower detection limit of 3.26 × 10-6 ng/mL and demonstrated the feasibility of serum sample detection, providing a novel and viable approach for the unmet clinical need of PD-L1 quantification. More importantly, the charge separation mechanism at the heterojunction interface proposed in this study provides new creative inspiration for designing sensors with high-sensitivity PEC performance.

Studies on the Light-Induced Phase Transition of CsPbBr3 Metal Halide Perovskite Materials.

We investigate the internal mechanism of the light-induced phase transition of CsPbBr3 perovskite materials via density functional theory simulations. Although CsPbBr3 tends to appear in the orthorhombic structure, it can be changed easily by external stimulus. We find that the transition of photogenerated carriers plays the decisive role in this process. When the photogenerated carriers transit from the valence band maximum to conduction band minimum in the reciprocal space, they actually transit from Br ions to Pb ions in the real space, which are taken away by the Br atoms with higher electronegativity from Pb atoms during the initial formation of the CsPbBr3 lattice. The reverse transition of valence electrons leads to the weakening of bond strength, which is proved by our calculated Bader charge, electron localization function, and integral value of COHP results. This charge transition releases the distortion of the Pb-Br octahedral framework and expands the CsPbBr3 lattice, providing possibilities to the phase transition from the orthorhombic structure to tetragonal structure. This phase transition is a self-accelerating positive feedback process, increasing the light absorption efficiency of the CsPbBr3 material, which is of great significance for the widespread promotion and application of the photostriction effect. Our results are helpful to understand the performance of CsPbBr3 perovskite under a light irradiation environment.

Multiphoton absorption properties and bioimaging of solvent coligand cyclometalated Pt(II) complex

As a cyclometalated complex, solvent coligand Pt(II) complex with multiphoton absorption has been designed and synthesized. After the optical properties of the Pt(II) complex were studied carefully, time-dependent density functional theory calculation (TD-DFT) was used to further identify the triplet charge transitions of the complex. The specific energy levels of frontier molecular orbitals and the data related to the energy level transition showed that the Pt(II) complex had photoluminescent properties, and their phosphorescence emission originated from 3LLCT/3MLCT. Because of nonlinear optics (NLO) response, the Pt(II) complex could act as multiphoton absorption materials for bioimaging and anticancer application.

Stability of doped and undoped ScNbO4 compound: Insight from first principle calculations

The quest for potential applications for a newly synthesized material is pragmatic and essential for building new devices. Doping it with rare-earth ions is one way to tune and approve its properties. We present a density functional calculation on the pristine and doped ScNbO4 compounds in this paper. In this context, we used the charged point defect procedure within the projector augmented wave method. The result of the phonon dispersion plot shows that ScNbO4 is dynamically stable in the monoclinic wolframite-type structure. According to the electronic calculations, ScNbO4 has a wide band gap, which favors a variety of UV and other optical applications, including the luminescence effect. To analyze the capability of the title compound as a host of doped rare-earth ions, a number of ions were evaluated by checking the site and growth conditions. Furthermore, the application of the Freysoldt methodology showed that the charge transition level in the doped ScNbO4 material has a stable valence band maximum under rich and poor Yb growing conditions. The analysis of the result shows that the p-type structure is more favorable to growth, paving the way for LED applications.

Design and synthesis of novel D-A copolymers based on fused thienothiophene for efficient broad absorption electrochromism

Developing conjugated polymers with broad spectrum modulation is highly desirable in electrochromic field. Herein, three novel polymers based on fused thienothiophene derivative (tris(thienothiophene) (TTT) or indacenodithieno[3,2-b]thiophene (IDTT)) and two acceptors (5,8-bis(4-(2-butyloctyl)thiophen-2-yl)-dithieno[3′,2':3,4; 2″,3'':5,6]benzo[1,2-c][1,2,5]thiadiazole (TBT) and 2,1,3-Benzothiadiazole (BT)) are synthesized via direct arylation polymerization (DArP). The neutral copolymers exhibit visibly broadband absorption due to the combination of the π-π* transition and intramolecular charge transfer absorption, which can be tuned by the feed ratio of the donor and acceptor monomers. As a result, the copolymer synthesized by IDTT, TBT and BT with a feed ratio of 3/2/1 presents a black color in the neutral state and high transparency in the oxidized state, which gives an average optical contrast of 34% in the visible band (400 nm–700nm), good stability and high coloration efficiency (370 cm2/C). Additionally, an electrochromic device with excellent electrochromic performance is fabricated based on the synthesized polymers. All of these confirm the synthesized polymers are attractive candidates for broad absorption electrochromism.

Cascade Charge Transitions of Unusually High and Mixed Valence Fe3.5+ in the A-Site Layer-Ordered Double Perovskite SmBaFe2O6.

The A-site layer-ordered double perovskite SmBaFe2O6 was obtained by topochemical of oxidizing A-site layer-ordered SmBaFe2O5 in ozone at a low temperature. The compound contained unusually high and mixed valence Fe3.5+ and was found to show cascade charge transitions, described as SmBaFe3.5+2O6 → SmBa(Fe3+Fe4+)O6 → SmBa(Fe3+Fe(4-δ)+0.5Fe(4+δ)+0.5)O6 → SmBa(Fe3+1.5Fe5+0.5)O6, to relieve its electronic instability. The first Verwey-like charge-order transition occurred at 340 K and was accompanied by a significant structural change and a sudden increase in magnetic susceptibility. The following transition was the charge disproportionation of metastable Fe4+ to Fe3+ and Fe5+, and each of the spins resulted in the antiferromagnetic ground state. The most plausible charge-ordered patterns are proposed based on the electrostatic lattice energy calculations.

A BF2 Chelate Exhibiting Excimer-like Fluorescence with an Unusually Large Stokes Shift in the Crystalline Phase.

The target mono-BF2 complex is weakly emissive in fluid solution because radiationless decay of the excited-singlet state is promoted through an intramolecular N⋅⋅⋅H-N hydrogen bond. The lack of mirror symmetry for this compound is attributed to vibronic effects, as reported previously for the bis-BF2 complex (BOPHY). Red-shifted fluorescence is observed from single crystals, the emission quantum yield approaching 30 % with a fluorescence lifetime of 2 ns. The large Stokes shift of 5,700 cm-1 helps minimize self-absorption. Crystallography indicates that the internal fold and twist angles are increased substantially in the crystal, but the hydrogen bond is weakened relative to solution. The crystal structure is compiled from pairs of head-to-tail molecules having a shift of ca. 4.1 Å and closest approach of ca. 3.5 Å. These molecular pairs are arranged in columns, which, in turn, assemble into sheets. The proximity favors excitonic coupling between individual molecules, with the coupling strength obtained by analysis of the absorption spectrum reaching ca. 1,000 cm-1 . Both the ideal dipole approximation and the extended dipole methodology seriously overestimate the coupling strength, but the atomic transition charge density procedure leads to good agreement with experiment. Emission is attributed to the closely coupled molecular pair functioning in an excimer-like manner with the exciton trapped in a local minimum. Increasing temperature causes a slight blue shift and loss of fluorescence.

Defects in WS2 monolayer calculated with a nonlocal functional: any difference from GGA?

Density functional theory (DFT) with generalised gradient approximation (GGA) functionals is commonly used to predict defect properties in 2D transition metal dichalcogenides (TMDs). Since GGA functionals often underestimate band gaps of semiconductors and incorrectly describe the character of electron localisation in defects and their level positions within the band gap, it is important to assess the accuracy of these predictions. To this end, we used the non-local density functional Perdew—Burke—Ernzerhof (PBE)0-TC-LRC to calculate the properties of a wide range of intrinsic defects in monolayer WS2. The properties, such as geometry, in-gap states, charge transition levels, electronic structure and the electron/hole localisation of the lowest formation energy defects are discussed in detail. They are broadly similar to those predicted by the GGA PBE functional, but exhibit numerous quantitative differences caused by the degree of electron and hole localisation in charged states. For some anti-site defects, more significant differences are seen, with both changes in defect geometries (differences of up to 0.5 Å) as well as defect level positions within the band gap of WS2. This work provides an insight into the performance of functionals chosen for future DFT calculations of TMDs with respect to the desired defect properties.

Shape and Satellite Studies of Highly Charged Ions X-ray Spectra Using Bayesian Methods

High-accuracy spectroscopy commonly requires dedicated investigation into the choice of spectral line modelling to avoid the introduction of unwanted systematic errors. For such a kind of problem, the analysis of χ2 and likelihood are normally implemented to choose among models. However, these standard practices are affected by several problems and, in the first place, they are useless if there is no clear indication in favour of a specific model. Such issues are solved by Bayesian statistics, in the context of which a probability can be assigned to different hypotheses, i.e., models, from the analysis of the same set of data. Model probabilities are obtained from the integration of the likelihood function over the model parameter space with the evaluation of the so-called Bayesian evidence. Here, some practical applications are presented within the context of the analysis of recent high-accuracy X-ray spectroscopy data of highly charged uranium ion transitions. The method to determine the most plausible profile is discussed in detail. The study of the possible presence of satellite peaks is also presented.

Multicomponent gauge-Higgs models with discrete Abelian gauge groups

We consider a variant of the charge-Q compact Abelian-Higgs model, in which an N f -dimensional complex vector is coupled with an Abelian gauge field. For and Q = 1 we observe several transition lines that belong to the O(4), O(3), and O(2) vector universality classes, depending on the symmetry breaking pattern at the transition. The universality class is independent of q as long as . The universality class of the transition is uniquely determined by the behavior of the scalar fields; gauge fields do not play any role. We also investigate the system for and Q = 2. In the presence of U(1) gauge fields, the system undergoes transitions associated with charged fixed points of the Abelian-Higgs field theory. These continuous transitions turn into first-order ones when the U(1) gauge fields are replaced by the discrete fields: in the present compact model charged transitions appear to be very sensitive to the nature of the gauge fields.

The role of epitaxial strain on photoconductive performance in LaNiO3 epitaxial thin films

In this work, LaNiO3 epitaxial thin films on (001) single-crystal LaAlO3 and SrTiO3 substrates were deposited by polymer assisted deposition method, respectively. Additionally, LaNiO3 polycrystalline film was coated on ceramic substrate using LaNiO3 powder obtained from precursor solution in polymer assisted deposition. Due to the difference of lattice mismatch between LaNiO3 and single-crystal substrates, LaNiO3 thin films suffer different epitaxial strain, resulting in distortion of NiO6 octahedrons which increases with the intensity of strain. Such phenomena lead to the decrease of the field splitting energy of NiO6 octahedron and the band gap value of LaNiO3, further increasing the charge transition and enhancing the visible-light photoconductivity. The existence of epitaxial strain brings more Ni2+ and adsorbed oxygen into perovskite type LaNiO3, introduces more oxygen vacancy defects, reduces the complex rate of photo induced electron-hole pairs, and thereby improves the photoelectric activity of LaNiO3. This work provides a feasible method to control the structure distortion and photoconductivity effect of all-inorganic perovskite.

Designing and theoretical study of benzocarbazole-based D-π-D type small molecules donor for organic solar cells

Seven new molecules (S1–S7) of D-π-D type have been designed for organic photovoltaic applications. The DFT and TD-DFT methods were used to investigate the effect of different central bridge groups on the geometric, optoelectronic, and charge transport properties of the constructed molecules. Among them, S4 and S6 have the lowest energy band gap and a red shift in the absorption spectra, revealing the perfect relationship between the central bridge and the strong electron withdrawal character through extended conjugation. Similarly, S6 explored the lowest reorganization energy (RE) value for electron and hole revealing its enhanced charge transition, also shows better ICT characteristics with its highest NLO properties. Compound S4 showed the smallest value of ΔEL−L and Eb, and the highest Voc due to its low HOMO, which improves the photocurrent density of the devices. Thus, the results suggest that bridge modification is a practical strategy to improve the efficiency of OSCs.

Synthesis, Characterization, and Properties of Sulfonated CNT‐Doped Poly(aniline‐co‐carbazole)‐PVA Conductive Films

AbstractConductive flexible films are successfully synthesized from polyvinyl alcohol matrix and poly(aniline‐co‐carbazole) charge carrier. To improve the mechanical properties of polyvinyl alcohol and promote charge transition in the conductive copolymer, dual purpose sulfonated multiwall carbon nanotube is added. Conductivity is enhanced via sulfonic acid protonic dopant and mechanical property is increased by its hexagonal nanorods. Nanocomposites are prepared by adding 0.025, 0.050, and 0.075 g of carbon nanotube which is added at 1%, 3%, and 5% loads to the polymer matrix. Films are characterized by infrared, UV–vis, X‐ray diffraction, scanning electron microscopy, and thermogravimetric analysis. Conductivity is measured by the four‐probe technique and mechanical property is assessed through tensile tests and dynamic mechanic thermal analysis. A 5 × 10−6 S cm−1 conductivity and 116 MPa tensile strength are recorded for the conductive film with optimum dopant/nanocomposite loads. The electrochemical property and corrosion resistance are studied by cyclic voltammetry and Tafel curves, respectively. The conductive films show an increase in corrosion potential and a decrease in corrosion current referring to a reliable corrosion protection film. The water uptake and contact angle of the films are measured to be 157% and 80.1° respectively to confirm its required hydrophilic property.

Dual-Emission Metal–Organic Framework for Highly Selective Ratiometric Sensing of Lithium(I) Ions in Aqueous Solution

The development of highly selective and sensitive detection methods for lithium ions in various environments, such as aqueous or battery application, is highly sought. However, it remains elusive due to the small radius and weak coordination ability of lithium ions. Considering a metal–organic framework (MOF) possesses plentiful open coordination sites and an adjustable pore size, the well-designed MOF would be an ideal platform for the selective detection of Li+. Herein, a novel dual-emission luminescent metal–organic framework with three-dimensional structure, namely, Co–HIAT, was prepared by the hydrothermal method and structurally characterized. The Co–HIAT MOF displays the ligand-based emission at 340 nm and the charge transition emission between the metal ions and ligand at 410 nm simultaneously. Hence, the first example of ratiometric fluorescence detecting of Li+ can be achieved by measuring the ratio of fluorescence at 410 to 340 nm in the fluorescent spectra of the Co–HIAT, which exhibits the outstanding sensitivity and selectivity, giving a detection limit down to 0.17 μM. Detailed experimental studies showed that the sensing mechanism involves the strong interactions of Li+ with the reasonable hydroxyl and carboxyl oxygen atoms in the Co–HIAT framework, which is responsible for the ratiometric change in fluorescence emission properties in the inclusion of Li+. It is worth noting that electrochemical experiments further confirmed its superior affinity for lithium ions. This work represents an important and feasible pathway to design MOFs for the detection of Li+.

Enhancing the Photovoltaic Properties via Incorporation of Selenophene Units in Organic Chromophores with A2-π2-A1-π1-A2 Configuration: A DFT-Based Exploration

Currently, polymer organic solar cells (POSCs) are widely utilized due to their significant application, such as low-cost power conversion efficiencies (PCEs). Therefore, we designed a series of photovoltaic materials (D1, D2, D3, D5 and D7) by the incorporation of selenophene units (n = 1-7) as π1-spacers by considering the importance of POSCs. Density functional theory (DFT) calculations were accomplished at MPW1PW91/6-311G (d, p) functional to explore the impact of additional selenophene units on the photovoltaic behavior of the above-mentioned compounds. A comparative analysis was conducted for designed compounds and reference compounds (D1). Reduction in energy gaps (∆E = 2.399 - 2.064 eV) with broader absorption wavelength (λmax = 655.480 - 728.376 nm) in chloroform along with larger charge transference rate was studied with the addition of selenophene units as compared to D1. A significantly higher exciton dissociation rate was studied as lower values of binding energy (Eb = 0.508 - 0.362 eV) were noted in derivatives than in the reference (Eb = 0.526 eV). Moreover, transition density matrix (TDM) and density of state (DOS) data also supported the efficient charge transition origination from HOMOs to LUMOs. Open circuit voltage (Voc) was also calculated for all the aforesaid compounds to check the efficiency, and significant results were seen (1.633-1.549 V). All the analyses supported our compounds as efficient POSCs materials with significant efficacy. These compounds might encourage the experimental researchers to synthesize them due to proficient photovoltaic materials.