Charge Transfer Energy Research Articles

Electronic correlations in epitaxial CrN thin film

Chromium nitride (CrN) spurred enormous interest due to its coupled magnetostructural and unique metal-insulator transition. The underneath electronic structure of CrN remains elusive. Herein, the electronic structure of epitaxial CrN thin film has been explored by employing resonant photoemission spectroscopy (RPES) and X-ray absorption near edge spectroscopy study in combination with the first-principles calculations. The RPES study indicates the presence of a charge-transfer screened 3d ^n{underline{L}} (L: hole in the N-2p) and 3d ^{n-1} final-states in the valence band regime. The combined experimental electronic structure along with the orbital resolved electronic density of states from the first-principles calculations reveals the presence of Cr(3d)-N(2p) hybridized (3d ^n{underline{L}}) states between lower Hubbard (3d ^{n-1}) and upper Hubbard (3d ^{n+1}) bands with onsite Coulomb repulsion energy (U) and charge-transfer energy (Delta) estimated as approx 4.5 and 3.6 eV, respectively. It verifies the participation of ligand (N-2p) states in low energy charge fluctuations and provides concrete evidence for the charge-transfer (Delta<U) insulating nature of CrN thin film.

Identifying A Universal Activity Descriptor and a Unifying Mechanism Concept on Perovskite Oxides for Green Hydrogen Production.

Producing indispensable hydrogen and oxygen for social development via water electrolysis shows more prospects than other technologies. Although electrocatalysts have been explored for centuries, a universal activity descriptor for both hydrogen-evolving (HER) and oxygen-evolving reactions (OER) has not been developed. Moreover, a unifying concept has not been established to simultaneously understand HER/OER mechanisms. Here, we rationally bridge the relationships between HER/OER activities in three common electrolytes and over 10 representative material properties on 12 3d-metal-based model oxides through statistical methodologies. Orbital charge-transfer energy (Δ) can serve as an ideal universal descriptor, where a neither too large nor too small Δ (∼1eV) with optimal electron-cloud density around Fermi level affords the best activities, fulfilling Sabatier's principle. Systematic experiments and computations unravel that pristine oxide with Δ ≈ 1eV possesses metal-like high-valence configurations and active lattice-oxygen sites to help adsorb key protons in HER and induce lattice-oxygen participation in OER, respectively. After reactions, partially generated metals in HER and high-valence hydroxides in OER dominate proton adsorption and couple with pristine lattice-oxygen activation, respectively. These can be successfully rationalized by the unifying orbital charge-transfer theory. This work provides the foundation of rational material design and mechanism understanding for many potential applications. This article is protected by copyright. All rights reserved.

Intrinsic Photoconductivity Spectral Dependence as a Tool for Prediction of Open-Circuit Voltage in Organic Solar Cells

Organic materials are known for their variety of molecules. Methods to predict the parameters of organic photovoltaic (OPV) cells are required to avoid the time- and resource-consuming processes of manufacturing and testing OPVs. Usually, the open-circuit voltage (Uoc) is estimated as the difference between the ionization energy level of the electron donor molecule (Id) and the electron affinity level of the electron acceptor molecule (EAa). Various measurement methods are used to determine the energy level values of pure materials, which, when combined with energy level shifts due to the donor:acceptor interactions, make these estimations less precise. In this work, photoconductivity measurements were applied to the donor:acceptor films. Near threshold energy, the electron can be directly transferred from the donor to the acceptor molecule. The obtained charge transfer energy (ECT) shows the difference between Id and EAa in the film. This difference was compared to the Uoc value of an OPV made of the same donor:acceptor combination. We show that this approach provides less scattered results and a higher correlation coefficient compared to the Uoc estimation using energy level values.

Linear Scaling Calculations of Excitation Energies with Active-Space Particle-Particle Random-Phase Approximation.

We developed an efficient active-space particle-particle random-phase approximation (ppRPA) approach to calculate accurate charge-neutral excitation energies of molecular systems. The active-space ppRPA approach constrains both indexes in particle and hole pairs in the ppRPA matrix, which only selects frontier orbitals with dominant contributions to low-lying excitation energies. It employs the truncation in both orbital indexes in the particle-particle and the hole-hole spaces. The resulting matrix, whose eigenvalues are excitation energies, has a dimension that is independent of the size of the systems. The computational effort for the excitation energy calculation, therefore, scales linearly with system size and is negligible compared with the ground-state calculation of the (N - 2)-electron system, where N is the electron number of the molecule. With the active space consisting of 30 occupied and 30 virtual orbitals, the active-space ppRPA approach predicts the excitation energies of valence, charge-transfer, Rydberg, double, and diradical excitations with the mean absolute errors (MAEs) smaller than 0.03 eV compared with the full-space ppRPA results. As a side product, we also applied the active-space ppRPA approach in the renormalized singles (RS) T-matrix approach. Combining the non-interacting pair approximation that approximates the contribution to the self-energy outside the active space, the active-space GRSTRS@PBE approach predicts accurate absolute and relative core-level binding energies with the MAEs around 1.58 and 0.3 eV, respectively. The developed linear scaling calculation of excitation energies is promising for applications to large and complex systems.

Atomic layer deposition of SnO2 on In2O3 enables ultrasensitive NO2 detection at room temperature and DFT mechanism research

The unique electronic and chemical properties of metal oxide heterostructures are critical to the development of room temperature (RT) sensors. In this work, we report the design of In2O3/SnO2 heterostructures based on atomic layer deposition (ALD), which regulates the energy band structure of the material and promotes the electron transfer, thus enhancing the adsorption of target gases. The sensor based on In2O3/SnO2 demonstrates outstanding sensing performance at RT with an extreme response of 2900 to 10 ppm NO2, which to our knowledge outperforms the reported metal oxide sensors, as well as a detection limit of 61 ppb. Density functional theory (DFT) calculations show that the charge transfer (0.494 e) and interaction energy (2.19 eV) between In2O3/SnO2 and NO2 are significantly enhanced. This work highlights the critical function of heterostructured materials in enhancing the sensing capabilities of semiconductors, providing some hints for the design of ultrasensitive NO2 sensors.

An electronic origin of charge order in infinite-layer nickelates

A charge order (CO) with a wavevector {{{{{{{bf{q}}}}}}}}simeq left(frac{1}{3},, 0,, 0right) is observed in infinite-layer nickelates. Here we use first-principles calculations to demonstrate a charge-transfer-driven CO mechanism in infinite-layer nickelates, which leads to a characteristic Ni1+-Ni2+-Ni1+ stripe state. For every three Ni atoms, due to the presence of near-Fermi-level conduction bands, Hubbard interaction on Ni-d orbitals transfers electrons on one Ni atom to conduction bands and leaves electrons on the other two Ni atoms to become more localized. We further derive a low-energy effective model to elucidate that the CO state arises from a delicate competition between Hubbard interaction on Ni-d orbitals and charge transfer energy between Ni-d orbitals and conduction bands. With physically reasonable parameters, {{{{{{{bf{q}}}}}}}}=left(frac{1}{3},, 0,, 0right) CO state is more stable than uniform paramagnetic state and usual checkerboard antiferromagnetic state. Our work highlights the multi-band nature of infinite-layer nickelates, which leads to some distinctive correlated properties that are not found in cuprates.

Ternary-Metal Sn-Pb-Zn Perovskite to Reconstruct Top Surface for Efficient and Stable Less-Pb Perovskite Solar Cells.

Though Sn-Pb alloyed perovskite solar cells (PSCs) achieved great progress, there is a dilemma to further increase Sn for less-Pb requirement. High Sn ratio (>70%) perovskite exhibits nonstoichiometric Sn:Pb:I at film surface to aggravate Sn2+ oxidation and interface energy mismatch. Here, ternary metal alloyed (FASnI3 )0.7 (MAPb1- x Znx I3 )0.3 (x = 0-3%) is constructed for Pb% < 30% perovskite. Zn with smaller ionic size and stronger ionic interaction than Sn/Pb assists forming high-quality perovskite film with ZnI6 4- enriched at surface to balance Sn:Pb:I ratio. Differing from uniform bulk doping, surface-rich Zn with lower lying orbits pushes down the energy band of perovskite and adjusts the interface energy for efficient charge transfer. The alloyed PSC realizes efficiency of 19.4% at AM1.5 (one of the highest values reported for Pb% < 30% PSCs). Moreover, stronger bonding of Zn─I and Sn─I contributes to better durability of ternary perovskite than binary perovskite. This work highlights a novel alloy method for efficient and stable less-Pb PSCs.

Probing the effect of Y3+/Gd3+ on the optical properties of Gd2-xYxTiO5:Eu3+: Insight into local site-luminescence correlation

Phosphor converted light emitting diodes (pcLEDs) are considered as the most efficient materials to resolve the issue of energy scarcity. In this regard, the design of an efficient red phosphor could be a game changer due to the lack of the same in the current existing phosphor library. Here in this work, we have investigated high color purity, moderate photoluminescence quantum yield (PLQY) and long excited state lifetime red emitting Gd2-xYxTiO5:1.0 %Eu3+ phosphor with varying Y3+/Gd3+ ratio. It was found that higher Y3+ containingGd0.5Y1.50TiO5:1% Eu3+ emerged victorious in terms of luminescence intensity, asymmetry ratio and PLQY ∼ 10 %. Higher PLQY of this particular composition has been attributed to lowest non-radiative channels in them. The same has been further supported by PALS as it suggested lowest defect density in Gd0.5Y1.50TiO5:1% Eu3+ as most of the vacancies have moved out of the lattice to the surface and is responsible for improved optical properties as defect triggered non-radiative pathways reduced significantly. The O2–→ Eu3+ charge transfer energy on the other hand eases in higher gadolinium counterparts owing to more structural distortion of distorted pentagonal bipyramid (DPB) and distorted hexagonal bipyramid (DHB) in them. Based on the number of Stark components of 5D0→7F0 there are two types of Eu3+ with distinct chemical environments. It was inferred that longer lived trivalent europium ions are the one located at a less distorted DPB whereas short lived Eu3+is ascribed to the one occupying a highly distorted DHB. The trend in Judd-Ofelt parameter Ω4 < Ω2 revealed that Eu3+ ions are localized in high asymmetric locations in all the samples under the doping level used in this work. The high branching ratio of 5D0→7F2 transitions for all the samples reflected in very high color purity of more than 99 %. These results suggest that Eu3+doped A2TiO5 luminescent crystals with moderate PLQY, high red color purity and long excited state lifetime could serve as efficient red phosphor and with further improvement can be potential candidate for various applications.

Synergistic Effect between Fe&lt;sup&gt;4+&lt;/sup&gt; and Co&lt;sup&gt;4+&lt;/sup&gt; on Oxygen Evolution Reaction Catalysis for CaFe&lt;sub&gt;1−&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Co&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt;

Chemical substitution is an effective way to improve electrocatalytic properties in transition metal oxides. We investigate the synergistic effect between Fe4+ and Co4+ ions on the catalytic activity for oxygen evolution reaction (OER) in the Fe-Co-mixed perovskite oxide CaFe1–xCoxO3. The OER activity of CaFe1–xCoxO3 is substantially increased by small amounts of Co (Fe) doping into CaFeO3 (CaCoO3), leading to the superiority compared to the pure Fe and Co perovskite oxides. The x dependences of the OER overpotential and specific activity for CaFe1–xCoxO3 (0.05 ≦ x ≦ 0.95) are expressed by constant offset from the weighted average between CaFeO3 and CaCoO3, which can be interpreted to be the synergistic effect between Fe4+ and Co4+ ions on OER activity. The absence of the optimum x for the highest activity for CaFe1–xCoxO3 contrasts with the volcano-like plots reported in various mixed-metal oxides. First-principle calculations using the special quasirandom structure models on CaFe1–xCoxO3 (x = 0.03–0.5) demonstrate that about half the amount of Fe4+ is electronically activated to possess smaller charge-transfer energies, corroborating the enhancement of catalytic activity in CaFe1–xCoxO3. These findings provide new insight into the synergistic effects in complex transition metal oxide catalysts.

Nonfused Ring Electron Acceptors for Ternary Polymer Solar Cells with Low Energy Loss and Efficiency Over 18.

Ternary polymer solar cells(PSCs) have been identified as an effective approach to improving power conversion efficiency (PCE) of binary PSCs. However, most of the third component, especially Y-series non-fullerene acceptors, is a fused ring acceptor which often requires a rather tedious synthesis and the use of hazardous organostannane reagents. In this work, two nonfused ring acceptors IOEH-4F and IOEH-N2F are synthesized by a green synthetic route and incorporated into PM6:Y6 blend. Encouragingly, the IOEH-4F and IOEH-N2F-based ternary PSCs exhibited more efficient charge transfer, exciton separation, and lower energy loss than PM6:Y6-based PSCs. And the IOEH-4F and IOEH-N2F-based ternary PSCs achieved an impressive PCE of 17.80% and 18.13%, respectively, which are higher than that of PM6:Y6 based PSCs (16.18%). Notably, these PCE values are also the highest PCEs for ternary PSCs including non-fused ring acceptors. Importantly, even when the IOEH-N2F:Y6 ratios increased from 0.05:1.2 to 0.50:1.2, the PCE of IOEH-N2F-based ternary PSCs (16.70%) are still higher than that of PM6:Y6 based PSCs, indicating the great potential for cost saving. It is believed that the findings will help the design of better nonfused ring acceptors and the optimization of corresponding ternary PSCs with cost-saving advantage.

Mn doped CoFe layered double hydroxides lead to d-d orbital repulsion toward advanced electrocatalysts for oxygen evolution reaction

Currently, developing highly active and low-cost electrocatalytic materials for oxygen evolution reaction (OER) is an enormously grand challenge. Herein, we developed a novel and highly active Mn doped Co2Fe layer double hydroxide (LDH) electrocatalyst for OER. We discovered that these electrocatalytic materials can be directly grown on carbon papers to construct high-specific-surface-area electrode, which shows the lowest overpotential of 266 mV at 10 mA cm−2. Furthermore, after introducing Mn element, DFT + U calculation found that the ∗OOH of Fe-site on Co2Fe0.67Mn0.33 LDH could draw more electrons than Co2Fe LDH due to the electronegativity differences between Fe-site on Co2Fe0.67Mn0.33 LDH and Fe-site on Co2Fe LDH, which is reason that the energy level of Fe 3d (eg) was obviously downshifted by d-d repulsion of Mn 3d and Fe 3d in the neighboring sites of Co2Fe0.67Mn0.33 LDH after doped Mn element, which leads to reduce charge-transfer energy from O 2p to Fe 3d (eg) to promote oxygen evolution processes for OER. Meanwhile, the band gap is also decreased after doped Mn element in Co2Fe LDH due to the downshifted eg orbital energy of Fe 3d. This study gives a general avenue to design and developing efficiently active LDH electrocatalysts for OER in the future.

Hierarchical MoN@NiFe-LDH Heterostructure Nanowire Array for Highly Efficient Electrocatalytic Hydrogen Evolution.

The slow charge transfer and high energy barrier are the key restrictions of cost-effective electrocatalysts for hydrogen production. A hierarchical heterostructure of MoN@NiFe-layered double hydroxides (LDH) is developed, with NiFe-LDH nanosheets supported on MoN nanowire arrays. The as-prepared MoN@NiFe-LDH exhibits a remarkably high performance on hydrogen production in alkaline medium, which is close to the benchmark Pt/C. The theoretical computations indicate that MoN@NiFe-LDH has a metallic character inherited from MoN, which gives rise to the promoted charge transfer. Furthermore, the adsorption intensity of intermediates on MoN@NiFe-LDH is optimized and thereby the energy barrier is diminished. This work demonstrates the significance of constructing heterostructure for boosting the charge transfer and reducing the energy barrier, which can shed light on the development of highly efficient and low-cost electrocatalyst for hydrogen production.

Charge Distribution across Capped and Uncapped Infinite-Layer Neodymium Nickelate Thin Films.

Charge ordering (CO) phenomena have been widely debated in strongly-correlated electron systems mainly regarding their role in high-temperature superconductivity. Here, the structural and charge distribution in NdNiO2 thin films prepared with and without capping layers, and characterized by the absence and presence of CO are elucidated. The microstructural and spectroscopic analysis is done by scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) and hard X-ray photoemission spectroscopy (HAXPES). Capped samples show Ni1+ , with an out-of-plane (o-o-p) lattice parameter of around 3.30 Å indicating good stabilization of the infinite-layer structure. Bulk-sensitive HAXPES on Ni-2p shows weak satellite features indicating large charge-transfer energy. The uncapped samples evidence an increase of the o-o-p parameter up to 3.65 Å on the thin film top with a valence toward Ni2+ in this region. Here, 4D-STEM demonstrates (303)-oriented stripes which emerge from partially occupied apical oxygen. Those stripes form quasi-2D coherent domains viewed as rods in the reciprocal space with Δqz ≈ 0.24 reciprocal lattice units (r.l.u.) extension located at Q = ( ) and ( ) r.l.u. The stripes associated with oxygen re-intercalation concomitant with hole doping suggest a possible link to the previously reported CO in infinite-layer nickelate thin films.

Thickness dependent OER electrocatalysis of epitaxial thin film of high entropy oxide

High entropy oxides (HEOs), which contain multiple elements in the same crystallographic site, are a promising platform for electrocatalysis in oxygen evolution reaction (OER). Investigating these materials in epitaxial thin film form expands the possibility of tuning OER activity by several means, which are not realizable in polycrystalline samples. To date, very few such studies have been reported. In this work, the OER activity of single-crystalline thin films of (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)NiO3, grown on NdGaO3 substrates have been investigated in 0.1 M KOH electrolyte as a function of film thickness. The OER activity increases with the thickness of the film. X-ray absorption spectroscopy measurements find an increase in Ni d-O p covalency and a decrease in charge transfer energy with the increase in film thickness. These facilitate higher charge transfer between Ni and surface adsorbates, increasing OER activity. However, the OER process leads to excessive leaching of thicker films and the OER activity of a 75 unit cell thick film is found to be optimal in the present study. This work demonstrates that the thickness of perovskite oxides can be used as a parameter to enhance OER activity.

Structure, chemical reactivity, NBO, MEP analysis and thermodynamic parameters of pentamethyl benzene using DFT study

This study explores the structural, molecular and electronic properties of the pentamethyl benzene (PMB) using quantum chemical calculations employing DFT/ B3LYP/6–311++G(d,p) level of theory. Structural parameters, HOMO-LUMO energies, chemical reactivity descriptors and molecular electrostatic potential (MEP) were evaluated from the optimized molecular geometry. The computed small band gap energy, correlated with the UV–visible spectrum, demonstrates that the test molecule has good biological activity. NLO activity of the molecule was also studied by evaluating dipole moment and first order hyperpolarizability values. Intra-molecular charge transfer, donor-acceptor transitions and stabilizations energies were determined from the analyses of natural bond orbital (NBO) and natural population. 1H and 13C chemical shifts were computed from the simulated NMR spectrum following GIAO approach in DMSO‑d6 solvent at the same level of DFT. Furthermore, thermodynamic parameters and rotational constants were also calculated for this molecule.

On the Role of Charge Transfer in Many-Body Non-Covalent Interactions.

Charge transfer is one of the mechanisms involved in non-covalent interactions. In molecular dimers, its contribution to pairwise interaction energies has been studied extensively using a variety of interaction energy decomposition schemes. In polar interactions such as hydrogen bonds, it can contribute ten or several tens of percent of the interaction energy. Less is known about its importance in higher-order interactions in many-body systems, mainly because of the lack of methods applicable to this problem. In this work, we extend our method for the quantification of the charge-transfer energy based on constrained DFT to many-body cases and apply it to model trimers extracted from molecular crystals. Our calculations show that charge transfer can account for a large fraction of the total three-body interaction energy. This also has implications for DFT calculations of many-body interactions in general as it is known that many DFT functionals struggle to describe charge-transfer effects correctly.

Engineering push–pull structural versatility in highly functional carbazole-based hole transporting materials design for efficient perovskites solar devices

This study proposes a push–pull molecular engineering strategy to design highly functional hole transport materials (HTMs) for perovskite solar cells (PSCs). The strategy involves introducing acceptor-anchor groups via benzene spacer to the versatile carbazole core containing dimethoxytriphenylamine side groups, resulting in a series of nine newly designed HTM moieties (BEN-A1 to BEN-A9). Quantum simulation protocols using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods were employed to investigate the designed HTMs. Our results demonstrate that the designed HTMs exhibit promising charge separation and transport throughout the molecule with lower spatial hole-electron overlap at the carbazole core, resulting in 98% intrinsic charge transfer and small exciton binding energy (0.003–0.108 eV). The HTMs also exhibit stabilized HOMO energy levels (by up to 0.13 eV) approaching the threshold (−5.38 eV) with appropriate HTM/Perovskite energy levels alignment, suggesting excellent charge extraction and higher VOC. Optical analysis shows that our proposed HTMs exhibit large stokes shift values (82–108 nm) and transparent absorption in broader visible region, enabling full utilization of light for perovskite layer for photocurrent generation, efficient energy conversion, reduced thermalization losses, and improved spectral selectivity. The HTMs exhibit smaller hole reorganization energy (0.111–0.137 eV) and higher transfer integral, indicating robust hole mobility owing to enhanced carbazole core functionality. Furthermore, higher negative solvation-free energy values (−16.19 to −20.89 kcal/mol) and elevated dipole moments imply better solubility and surface-wetting properties. Overall, this study broadens our understanding of push–pull molecular engineering for versatile carbazole-based HTMs, which have immense prospects for efficient and functional application in PSCs.

Effect of different solvents, molecular level vibrational energies, electronic, electrostatic, donar-acceptor and pharmaceutical studies on 3-methoxy phenyl acetonitrile- anti depressant agent

The most economical method for analyzing molecular structure is density functional theory (DFT), which has several applications in the study of vibrational spectrum biological systems. In the context of biological in addition to NLO behavior, the density functional theory (DFT) technique has numerous purposes. It turned out to be the most financially sound approach for examining molecular geometry. 3-Methoxy phenyl acetonitrile (3MPAN) has been optimized and its skeletal parameters were computed using the basis function 6–311++ G(d,p). HOMO and LUMO analytics have been used to determine the transfer of charge within the molecule. By detecting internal charge transfer, hyperconjugation, and stabilization energy, the NBO research has been used to confirm the molecule's stability. Mulliken's charges and molecular electrostatic potential were thoroughly investigated utilizing DFT techniques. B3LYP basis functionals were used to look at the NLO properties of the drug molecule. Condensed Fukui functions and global descriptors have been extensively used to study the reactive sites and reactivity of the pharmacological molecule. 29.85 Kcal/mol equilibrium energy is the greatest one occurred between O1 of LP(2) to π*(C5-C8). In order to investigate solvation analysis, various solvents were used. Solvents drastically altered the molecule's global characteristics and structural reactivity. Compared to other sol-vents, methonal has the largest band gap value of 5.619 eV. The substance under study has extraordinary NLO (non-linear optical) characteristics. For both the gas phases and solvents, ELF, LOL and RDG were stimulated. Although and drug-likeness were used to support the bioactivities. The fact that this chemical adheres to five Lipinski's rule means therefore, ingesting effective dose of similar compounds should not pose an issue. The results of docking studies demonstrated the effectiveness of the ligand under research as an anti-depressant medication.

Electroactive site enriched battery-type worm-like cobalt tungstate nanoarchitecture electrode material for performance-enhanced hybrid supercapacitor

The supercapacitor performances of stable and highly efficient electrode materials crucially depend on their physicochemical parameters, which are influenced by the preparation conditions and techniques. Herein, the worm-like CoWO4 (CWO) nanoarchitecture is achieved through a facile hydrothermal method followed by pyrolysis. The effect of pyrolysis temperature on the physicochemical properties, such as crystallinity, surface area, porosity, particle size, and morphology of the prepared CWO nanomaterials, is examined. From these observations, the pyrolyzing temperature significantly impacts the physicochemical characteristics and the associated electrochemical performances. Further, the final product's crystallite size increases, and surface area concomitantly fall from 16 to 34 nm and 26.1–12.9 m2 g−1, respectively, as the pyrolyzing process is increased from 400 to 600 °C. The distinct morphological feature of worm-like CWO-A nanostructure pyrolyzed at 400 °C is advantageous to have effective charge transfer and large energy storage capacity. Markedly, the worm-like CWO-A electrode depicts a superior specific capacity of 445 and 284 C g−1 at 1 and 20 A g−1, respectively, suggesting an excellent rate performance. Moreover, the constructed hybrid supercapacitor (CWO-A//AC) attains a maximum energy density of 41.38 Wh kg−1 at a power density of 627.42 W kg−1 with an outstanding long-term cyclic retention and ∼9.3% of capacity loss for 10,000 cycles. Thus, this study highlights that the distinct worm-like CWO-A nanostructure could be a suitable electrode material for supercapacitor applications.

An ICT-FRET-based ratiometric fluorescent probe for hydrogen polysulfide based on a coumarin-naphthalimide derivative

Hydrogen polysulfide (H2Sn, n > 1), as one of the important members of reactive sulfur species (RSS), plays a vital part in the processes of both their physiology and pathology. In this work, a ratiometric fluorescent probe for H2Sn had been designed and prepared based on the combination mechanism of intramolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET). The probe chose a coumarin derivative as the energy donor, a naphthalimide derivative as the energy acceptor and 2-fluoro-5-nitrobenzoate as the H2Sn recognition group. When H2Sn was not present in the system, the ICT process of the naphthalimide acceptor was inhibited and the FRET process from the coumarin donor to the naphthalimide acceptor was turned off. When H2Sn was added, both ICT and FRET occurred due to the nucleophilic substitution-cyclization reactions between the probe and hydrogen polysulfide. In addition, the ratio value of the emission intensities at 550 nm and 473 nm (I550 nm/I473 nm) of this probe had a good linear relationship with H2Sn concentration in the range of 6.0 × 10-7-5.0 × 10-5 mol·L-1, and a detection limit of 1.8 × 10-7 mol·L-1 was obtained. The developed probe had high selectivity and sensitivity, as well as good biocompatibility. Additionally, the probe had been used to successfully image both indigenous and exogenous hydrogen polysulfide in A549 cells using confocal microscope.