Electron Cloud Distribution Research Articles

Boosting Electrochemical Nitrate Reduction to Ammonia by Fe Doped CuO/Co3O4 Nanosheet/Nanowire Heterostructures.

The electrochemical nitrate reduction reaction (NO3-RR) is a novel green method for ammonia synthesis. The development of outstanding NO3-RR performance is based on reasonable catalyst. Metal oxides have garnered significant attention due to their exceptional electrical conductivity and catalytic properties. Doping serves as an effective strategy for enhancing catalyst performance due to its ability to change the electron cloud distribution and energy levels. In this study, we develop a heterojunction catalyst Fe doped copper oxide nanosheet and cobalt tetroxide nanowire growing on carbon cloth simultaneously (Fe-CuO@Co3O4/CC) via hydrothermal method. The well-designed Fe-CuO@Co3O4/CC has excellent NH3 yield (470.9 μmol h-1 cm-2) and Faraday efficiency (FE: 84.4%) at -1.2 V versus reversible hydrogen electrode (vs. RHE). The heterostructure increases the specific surface area of the catalyst, and the possibility of contact between the catalyst and NO3- ions, enhances the catalytic efficiency. In addition, the catalyst has excellent stability and can stably carry out the electrocatalytic nitrate reduction reaction (NO3-RR), which provides a way for further research on the high-efficiency reduction of nitrate.

Biological template hydrothermal synthesis of hollow La-doped one-dimensional CaMnO3 fibers and their enhanced microwave absorption performance

The advancement of military technology, 5G communication, and electronic equipment has increased the demand for efficient electromagnetic wave absorption materials. Calcium manganate (CaMnO3) is a commonly used dielectric absorber due to its excellent dielectric polarization effect. However, traditional ceramic materials like CaMnO3 have low conductivity, making it difficult to achieve impedance matching and electromagnetic loss simultaneously. In this work, to address this issue and create ideal wave-absorbing materials, one-dimensional La-doped CaMnO3 materials were synthesized using a simple biological template hydrothermal method. By studying the relationship between doping content and electromagnetic parameters, it was found that the La-doped CaMnO3 material exhibited excellent electromagnetic wave absorption properties, with a minimum reflection loss (RLmin) of −73.62 dB and a maximum effective absorption bandwidth of 3.3 GHz in the X-band. The introduction of La elements, which have different electronegativities from Ca ions, altered the electron cloud distribution in the sample, leading to the formation of electric dipoles that disrupt charge distribution and dissipate electromagnetic waves. The dielectric loss in fibrous La-doped CaMnO3 is mainly due to interfacial polarization. The fibrous structure allows for increased contact area with the air medium, while the porous structure introduces air bubbles that alter the dielectric properties between the sample and the air medium. This not only enhances impedance characteristics to some extent but also triggers interfacial polarization. Both of these factors help improve the material's ability to absorb electromagnetic waves. The successful creation of this one-dimensional absorbing material opens up possibilities for developing new one-dimensional absorbing materials using a straightforward method.

Application of Mesoporous Carbon-Based Highly Dispersed K-O2 Strong Lewis Base in the Efficient Catalysis of Methanol and Ethylene Carbonate.

As an atom-economical reaction, the direct generation of dimethyl carbonate (DMC) and ethylene glycol (EG) via the transesterification of CH3OH and ethylene carbonate (EC) has several promising applications, but the exploration of carriers with high specific surface areas and novel heterogeneous catalysts with more basic sites remains a long-standing research challenge. For this purpose, herein, a nitrogen-doped mesoporous carbon (NMC, 439 m2/g) based K-O2 Lewis base catalyst (K-O2/NMC) with well-dispersed strongly basic sites (2.23 mmol/g, 84.5%) was designed and synthesized. The compositions and structures of NMC and K-O2/NMC were comprehensively investigated via Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, CO2 temperature-programmed desorption, and contact angle measurements. The optimal structural configuration and electron cloud distribution of the K-O2/NMC catalyst were simulated using first-principles calculations. The electron transfer predominantly manifested as a flow from K-O to C-O/C-N, and the interatomic interactions between each atom were enhanced and exhibited a tendency for a more stable state after redistribution. Furthermore, the adsorption energies (Eads) of CH3OH at K-O-O and K-O-N sites were -1.4185 eV and -1.3377 eV, respectively, and the O atom in CH3OH exhibited a stronger adsorption tendency for the K atom at the K-O-O site. Under the optimal conditions, the EC conversion, DMC/EG selectivity, and turnover number/frequency were 80.9%, 98.6%/99.4%, and 40.5/60.8 h-1, respectively, with a reaction rate constant (k) of 0.1005 mol/(L·min). Results showed that the heterogeneous K-O2/NMC catalyst prepared herein greatly reduced the reaction cost while guaranteeing the catalytic effect, and the whole system required a lower reaction temperature (65 °C), a shorter reaction time (40 min), and a lower catalyst amount (2.0 wt % of EC). Therefore, K-O2/NMC can be used as a catalyst in different transesterification reactions.

Terminal conversion of polyamide membranes by homologous monomer vapors for chlorine-resistant desalination

Water scarcity is a global challenge and severely threatens human development. Membrane desalination shows great potential for producing freshwater from saltwater to alleviate this crisis. However, the dominating polyamide membranes suffer from the issue of poor chlorine resistance, which cause performance deterioration and shortens membrane lifespan. In this study, we report a concept of terminal conversion to design high-performance, antifouling, and especially chlorine-resistant polyamide desalination membranes. This amino-to-carboxyl conversion of commercial membranes can be simply performed by controllable and scalable chemical vapor deposition through exposure in homologous monomer vapor and hydrolysis of unreacted acyl chloride groups. We demonstrate that this conversion not only adjust the electronegativity and hydrophilicity of membranes to boost fouling resistance and reverse osmosis performance, but also tune the reactivity and electron cloud distribution of polyamide networks to restrain chlorine accessibility and substantially improve anti-chlorination property. After extreme chlorination for 240000 ppm h, the resultant membranes show limited rejection decline of only 7.2 %. For high-salinity (35000 ppm) and high-pressure (38 bar) desalination, the modified membranes before and after chlorination for 144000 ppm h still exhibit rejection of 94.5 % and 90.0 % and flux of 75.2 and 71.4 L m−2 h−1, respectively, which are much better than those of the pristine membranes (89.6 % and 63.5 %, and 64.2 and 57.5 L m−2 h−1). Our findings pave an alternative mechanism and strategy to reconstruct polyamide membranes for efficient water desalination.

Interlayer Polymerization to Construct a Fully Conjugated Covalent Organic Framework as a Metal-Free Oxygen Reduction Reaction Catalyst for Anion Exchange Membrane Fuel Cells.

Two-dimensional (2D) covalent organic frameworks (COFs) have a multilayer skeleton with a periodic π-conjugated molecular array, which can facilitate charge carrier transport within a COF layer. However, the lack of an effective charge carrier transmission pathway between 2D COF layers greatly limits their applications in electrocatalysis. Herein, by employing a side-chain polymerization strategy to form polythiophene along the nanochannels, a conjugated bridge is constructed between the COF layers. The as-synthesized fully conjugated COF (PTh-COF) exhibits high oxygen reduction reaction (ORR) activity with narrowed energy band gaps. Correspondingly, PTh-COF is tested as a metal-free cathode catalyst for anion exchange membrane fuel cells (AEMFCs) which showed a maximum power density of 176mWcm-2 under a current density of 533mAcm-2. The density functional theory (DFT) calculation reveals that interlayer conjugated polythiophene optimizes the electron cloud distribution, which therefore enhances the ORR performance. This work not only provides new insight into the construction of a fully conjugated covalent organic framework but also promotes the development of new metal-free ORR catalysts.

BioAIEgens based on dehydroabietic acid and tetraphenylethene: How does isopropyl group of dehydroabietic acid affect their spectral performance

Based on dehydroabietic acid (DA) derived from natural rosin, two aggregation-induced emission luminogens (BioAIEgens) labeled as 12-DTPA-2pTPE and 13-DTPA-2pTPE were synthesized by introducing tetraphenylethylene (TPE) groups to dehydroabietic acid triarylamine (DTPA). Their structures were optimized, the spectral properties and AIE characteristics were investigated, and the compounds were prepared into nanoparticles (NPs) as fluorescent probes for cell imaging. The results show that the two BioAIEgens have typical AIE characteristics and large Stokes shifts (＞ 120 nm). Due to the electronic and spatial effects of the isopropyl group, the molecular configuration of 12-DTPA-2pTPE is more distorted, and the electron cloud distribution is also different from 13-DTPA-2TPE. The absorption and the emission peaks of 12-DTPA-2TPE are blue-shifted, and the fluorescence quantum yield in the solid is higher. In addition, the 13-DTPA-2TPE nanoparticles (NPs) have low cytotoxicity and good cell imaging effects in vitro.

Red Fluorescent Molecule with Aggregation-Induced Emission Based on Dehydroabietic Acid Diarylamine for Bioimaging.

In this paper, molecules with AIE red light properties were designed by coupling dehydroabietic acid diarylamine and 2,3-diphenylfumaronitrile, which were designated 2DTPA-CN and 2TPA-CN. The emission wavelengths were 683nm and 701nm, respectively. The 2DTPA-CN and 2TPA-CN showed typical AIE characteristics with large Stokes shifts of 7.4 × 104 cm-1 and 6.7 × 104 cm-1, respectively. The obvious solvatochromism and electron cloud distributions of HOMO/LUMO in the ground and excited states both reveal the intramolecular charge transfer (ICT) effect. The 2DTPA-CN, boasting exceptional biocompatibility, was successfully prepared into nanoparticles (NPs), which were applied to tumor cell imaging, showing good bioimaging effects both in vitro imaging in live cells and in vivo imaging in live mice. The results demonstrated that it possesses significant potential as an effective bioimaging reagent for the detection of tumor cells. Furthermore, the incorporation of 2,3-diphenylfumaronitrile moieties to dehydroabietic acid diarylamine emerged as a proficient approach to broaden the emission wavelengths of rosin-based fluorescent materials.

Electrophile-mediated ionic liquid strategy for transforming inert natural polymers into highly active iodine adsorbents

The separation and conversion of gas resources are crucial aspects of sustainable energy development. Developing general methods to overcome bottlenecks in gas adsorption and conversion within natural polymers is an urgent global concern. In this work, the use of ionic liquids as electrophiles was proposed, and the Ionic Liquid Solution Process (ILSP) was employed to prepare alginate polymers-based on natural polymers. ILSP achieved a remarkable 0-to-1 transformation in gaseous iodine adsorption, converting inactive alginic acid (∼0 g g−1 in saturated adsorption capacity) into a highly active iodine adsorbent (5.24 g g−1). It was revealed that electrophiles effectively regulated the electron cloud distribution of functional groups by replacing acidic protons on alginic acid, exerting a volumetric effect. This increased the electron density near the deprotonated carboxylic groups, enhancing the nucleophilicity of carboxylic groups. Consequently, it promoted halogen interaction between electron-rich oxygen atoms and iodine during adsorption, thereby improving the efficiency of charge transfer complex formation and polyiodide ion conversion. The ILSP strategy could provide guidance for the separation and conversion of gases such as iodine, carbon dioxide, and hydrogen.

Structural identification, stability and combination mechanism of calcium-chelating wheat gluten peptides

Abstract In order to explore the structures and combination mechanism of wheat gluten peptides-calcium chelate (WOP-Ca) in depth, WOP-Ca were prepared by chelating wheat gluten peptides (WOP) with calcium. The yield of WOP-Ca was determined to be 51.2 ± 2.12 %, and it exhibited a calcium-chelating rate of 58.96 ± 1.38 %. The structural differences between WOP-Ca and WOP were characterized using various analytical techniques, and the results revealed that WOP-Ca and WOP differed in their microstructure, characteristic group absorption peaks, changes in electron cloud distribution, and thermal stability. WOP-Ca demonstrated remarkable stability and resistance to changes in pH, temperature, and in vitro digestion with gastric protease. After undergoing various treatments, the molecular weight distribution in each interval changed very little. Identification of the peptides in WOP-Ca was achieved by utilizing a mass spectrometer, and a total of 39 peptides were identified in WOP-Ca. Among these, 14 peptides with Score ≥ 30 and Coverage ≥ 20 showed bioavailability percentages exceeding 30 %, with half surpassing 50 %. The binding mode between the 14 peptides and Ca2+ was determined to be α linkage. The Ca–O bond lengths ranged from 2.40 to 3.20 Å, indicating the formation of structurally stable complexes. The carboxyl oxygen atoms played a crucial role in binding with Ca2+, with bond lengths ranging from 2.41 to 2.49 Å and 2.43 to 2.46 Å, respectively. The finding suggested that WOP-Ca prepared by chelation may be used as a calcium supplement that could serve as food additives, dietary nutrients, and pharmaceutical agents.

A novel ionic-liquid-mediated covalent organic framework as a strong electrophile for high-performance iodine removal

The research on the adsorption and conversion of non-polar gases (carbon dioxide, hydrogen, iodine, etc.) has attracted global attention. Extensive work has revealed the intuitive impact of the heteroatom effect on the adsorption performance of covalent organic framework (COF) adsorbents for non-polar gases. However, more influencing factors must be studied to more precisely design and construct target-specific COF adsorbents. In this work, an underlying influencing factor, local polarity, is discovered, which is defined as the polarity of the functional moiety. Due to the substitution of strong electrophile, the electron cloud distribution of the COF framework is regulated, and the local polarity that better matches the adsorption of target electrophilic gas (iodine) has been observed. The local polarity of COF has been controlled through several strong electrophilic ionic liquids, dramatically improving adsorption performance. The saturated adsorption capacity increases from 1.5 to 5.2 g·g−1, and the adsorption kinetics index k80% value increases from 0.51 to 2.69 g·g−1·h−1. The insight would support precise chemical regulation of target-specific COF in energy and environment science.

Research on the Stability of Different Polar Surfaces in Aluminum Nitride Single Crystals

Wurtzite aluminum nitride (AlN) crystal has a non-centrosymmetric crystal structure with only a single axis of symmetry. In an AlN crystal, the electronegativity difference between the Al atom and N atom leads to a distortion of electron cloud distribution outside the nucleus and a spontaneous polarization (SP) along the c-axis direction. The N-polar surface along the directions of [000-1] has higher surface energy than the Al-polar surface along the directions of [0001]. Due to the different atomic arrangement, Al atoms on the Al-polar surface bond with O and OH− in the environment to generate Al2O3·xH2O, which prevents the reaction from occurring inside the crystal. After the Al2O3·xH2O dissolve in an alkaline environment, N atoms have three dangling bonds exposed on the surface, which can also protect OH− from destroying the internal Al-N bonds, so the Al-polar surface is more stable than the N-polar surface.

Enhancing Reverse Intersystem Crossing of Multiple Resonance Type Thermally Activated Delayed Fluorescence Emitter by Introducing Spatial Perturbation

AbstractFor multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters, electron cloud distributions of their π‐conjugated planes are crucial for determining their eventual performance. Currently, modulation attempts of MR‐TADF emitters are mainly inside the π‐conjugated planes. Possible out‐of‐plane interactions may also significantly impact the photophysical properties, but the exploration is quite limited. Here, a novel concept of using out‐of‐plane (e.g., π–π and lone pair‐π) interactions to introduce spatial perturbation (SPPT) to improve TADF performance is proposed. Two newly developed MR‐TADF emitters, namely, o‐BNPO and BNPO, which both consist of a popular MR framework, DtBuCzB, and diphenylphosphine oxide (DPPO), are compared in depth. In particular, for o‐BNPO, evident π–π interaction is observed between one side of the DtBuCzB π‐conjugated plane and a phenyl ring from DPPO, and lone pair‐π interaction with the oxygen atom from DPPO is noticed on the other side, resulting in significantly accelerated reverse intersystem crossing and better TADF without sacrificing narrowband emission features. Ultimately, in organic light‐emitting diodes with sensitizer‐free emitting layers, both emitters achieve similar narrowband emissions, while the o‐BNPO‐based device demonstrates a much higher external quantum efficiency of 36% and milder efficiency roll‐off.

The local disorder induced by high-entropy doping results in highly stable cathode materials for aqueous potassium-ion batteries

Aqueous potassium-ion batteries are poised to become leading candidates for next-generation large-scale storage technology due to their low cost and safety features. However, the stability of aqueous potassium-ion battery materials faces significant challenges. The large ionic radius of potassium ions causes significant stress changes in the ordered crystal structure of the materials during the charge-discharge process. To address this issue, we synthesized high-entropy-doped layered manganese oxide (HE-KMO). High-entropy doping reconstructed the electron cloud distribution between the layers of HE-KMO, causing local disorder in HE-KMO. Local disorder reduces the transport barrier by inducing the transport of potassium ions and alleviates the stress on the material. It prevented phase transitions of HE-KMO during charging and discharging, improving the stability of HE-KMO. We used HE-KMO in the cathode material of aqueous potassium-ion batteries. Under a current of 5 A g−1, HE-KMO maintains an outstanding capacity retention after 5000 cycles.

Nitrogen-reliant degradation behaviors of characteristic NHCs by UV-based advanced oxidation processes: Kinetics, pathways and toxicity assessment

In recent decades, nitrogen-containing heterocyclic compounds (NHCs) have been widely synthesized and applied due to their excellent coordination capability of heterocyclic N atoms. However, their high toxicity and poor biodegradability pose significant hazards to aquatic ecosystems. Three characteristic NHCs (cNHCs) with similar molecular structures but minor differences in the number and position of N atoms, namely benzotriazole (BTA), benzimidazole (BMZ), and indazole (IDZ), were selected to evaluate impacts of these differences on their degradation behaviors during UV/H2O2 treatments. It was found that the key mechanism for the removal of BTA, BMZ, and IDZ in the UV/H2O2 processes was the generation of ∙OH through UV-excited H2O2 decomposition. Density functional theory (DFT) calculations revealed that the variation in the number and position of heterocyclic ring N atoms significantly affected the electron cloud distribution of the cNHCs, thereby resulting in different reactivities. Mineralization results and N evolution experiments indicated that N elements were initially released in the form of ammonia nitrogen during UV/H2O2 treatments, which then underwent oxidation to form nitrite and nitrate. The two ortho-N atoms were most easily mineralized and release inorganic nitrogen, followed by the two meta-N atoms. However, the BTA compound containing three N atoms, exhibited inertness towards radicals after hydroxylation, thereby hindering mineralization. A dual-directional transformation products (TPs) identification protocol was employed to identify 30 TPs of the cNHCs and propose recommended degradation pathways. Furthermore, Vibrio fischeri bioluminescence inhibition bioassay and QSAR prediction models were used to preliminarily screen and identify 13 toxic TPs with potential ecological risks.

Insight into the purification of arsenic-contaminated acid water by metal–organic framework MIL-53(Fe) with sulfite: The generation and effect of Fe(IV)

Iron based metal–organic frameworks (Fe-MOFs) have garnered international interest as a novel and promising category of adsorbent materials for the elimination of arsenic from neutral waters. Nevertheless, their practical implementation is constrained by their inadequate adsorption capacity for aqueous arsenite (As(III)), a prevalent arsenic species found in acidic environments such as acid mine drainage. Herein, a novel oxidation-adsorption process to effectively purify As(III)-contaminated water is constructed by combining the MIL-53(Fe) of high acid resistance with sulfite (S(IV)). Notably, the adsorption capacity of the MIL-53(Fe)/S(IV) process for As(III) at pH 3.5 reached 86.4 mg g−1, surpassing the values achieved by MIL-53(Fe) alone by 21.6 times for As(III) and 1.62 times for As(V) (oxidized As(III)). During the oxidation process, MIL-53(Fe) effectively activated S(IV), leading to the formation of the crucial intermediate SO5•−, which then underwent two distinct pathways to respectively generate Fe(IV) and SO4•−, accounting for rapid oxidation of As(III). In the adsorption process, the S(IV) activation (i.e., complexation and electron transfer) on the MIL-53(Fe) surface created additional adsorption sites by dredging the pores and altering the electron cloud distribution within the adsorbent. Furthermore, As(V) trended to form monodentate complexes with surface Fe (e.g., FeOAs bond) in the MIL-53(Fe)/S(IV) process. Notably, this oxidative removal process demonstrated reliable performance in complex water matrices and practical arsenic-contaminated waters. Overall, this study presents a promising strategy to enhance the efficacy of Fe-MOFs for the removal of As(III).

Restructuring Electrolyte Solvation by a Versatile Diluent Toward Beyond 99.9% Coulombic Efficiency of Sodium Plating/Stripping at Ultralow Temperatures.

The reversible and durable operation of sodium metal batteries at low temperatures (LT) is essential for cold-climate applications but is plagued by dendritic Na plating and unstable solid-electrolyte interphase (SEI). Current Coulombic efficiencies of sodium plating/stripping at LT fall far below 99.9%, representing a significant performance gap yet to be filled. Here, the solvation structure of the conventional 1m NaPF6 in diglyme electrolyte by facile cyclic ether (1,3-dioxolane, DOL) dilution is efficiently reconfigured. DOL diluents help shield the Na+-PF6 - Coulombic interaction and intermolecular forces of diglyme, leading to anomalously high Na+-ion conductivity. Besides, DOL participates in the solvation sheath and weakens the chelation of Na+ by diglyme for facilitated desolvation. More importantly, it promotes concentrated electron cloud distribution around PF6 - in the solvates and promotes their preferential decomposition. A desired inorganic-rich SEI is generated with compositional uniformity, high ionic conductivity, and high Young's modulus. Consequently, a record-high Coulombic efficiency over 99.9% is achieved at an ultralow temperature of -55°C, and a 1 Ah capacity pouch cell of initial anode-free sodium metal battery retains 95% of the first discharge capacity over 100 cycles at -25°C. This study thus provides new insights for formulating electrolytes toward increased Na reversibility at LT.

Construction and Application of Fluorescent Probes with Imine Protective Groups for Hypochlorite Detection.

Several fluorescent probes have been designed to detect ClO- in biological systems based on the isomerization mechanism of C = N bonds. Particularly, fluorescein has emerged as an important fluorophore for detecting ClO- because of its unique properties. Previously, we introduced the fluorescein analog F-1 with an active aldehyde group. In this study, two ClO- fluorescent sensors (F-2 and F-3) with imine groups were designed and synthesized using diaminomaleonitrile and 2-hydrazylbenzothiazole as amines. The electron cloud distribution of F-2 and F-3 in ground and excited states was explored via Gaussian calculations, reasonably explaining their photophysical properties. The fluorescence detection of ClO- in solution using the two probes (F-2 and F-3) was realized based on the mechanism of imine deprotection with ClO-. NaClO concentration titration demonstrated that the colorimetric detection of ClO- with the naked eye could be achieved using both F-2 and F-3. However, after adding ClO-, the fluorescence intensity of probe F-2 increased, whereas that of probe F-3 first decreased and then increased. Probes F-2 and F-3 exhibited good selectivity, anti-interference capability, and sensitivity, with the detection limits of 169.95 and 37.30 µM, respectively. Owing to their low cell toxicity, probes F-2 and F-3 can be applied to detect ClO- in vivo. The design approach adopted in this study will further advance the future development of ClO- chemical probes through the removal of C = N bond isomerization.

Understanding the Role of Fluorine Groups in Passivating Defects for Perovskite Solar Cells

AbstractIntroducing fluorine (F) groups into a passivator plays an important role in enhancing the defect passivation effect for the perovskite film, which is usually attributed to the direct interaction of F and defect states. However, the interaction between electronegative F and electron‐rich passivation groups in the same molecule, which may influence the passivation effect, is ignored. We herein report that such interactions can vary the electron cloud distribution around the passivation groups and thus changing their coordination with defect sites. By comparing two fluorinated molecules, heptafluorobutylamine (HFBM) and heptafluorobutyric acid (HFBA), we find that the F/−NH2 interaction in HFBM is stronger than the F/−COOH one in HFBA, inducing weaker passivation ability of HFBM than HFBA. Accordingly, HFBA‐based perovskite solar cells (PSCs) provide an efficiency of 24.70 % with excellent long‐term stability. Moreover, the efficiency of a large‐area perovskite module (14.0 cm2) based on HFBA reaches 21.13 %. Our work offers an insight into understanding an unaware role of the F group in impacting the passivation effect for the perovskite film.

Understanding the Role of Fluorine Groups in Passivating Defects for Perovskite Solar Cells ​.

Introducing fluorine (F) groups into a passivator plays an important role in enhancing the defect passivation effect for the perovskite film, which is usually attributed to the direct interaction of F and defect states. However, the interaction between electronegative F and electron-rich passivation groups in the same molecule, which may influence the passivation effect, is ignored. We herein report that such interactions can vary the electron cloud distribution around the passivation groups and thus changing their coordination with defect sites. By comparing two fluorinated molecules, heptafluorobutylamine (HFBM) and heptafluorobutyric acid (HFBA), we find that the F/-NH2 interaction in HFBM is stronger than the F/-COOH one in HFBA, inducing weaker passivation ability of HFBM than HFBA. Accordingly, HFBA-based perovskite solar cells (PSCs) provide an efficiency of 24.70% with excellent long-term stability. Moreover, the efficiency of a large-area perovskite module (14.0 cm2) based on HFBA reaches 21.13%. Our work offers an insight into understanding an unaware role of the F group in impacting the passivation effect for the perovskite film. ​.

Photophysical properties of several multi-branched oligomers: An ultrafast excited state dynamics and quantum chemical calculation study

Multi-branched oligomers F1, F2 and F3 were investigated by spectroscopic experiments as well as quantum chemical calculations to elucidate the structure–property relationships and intramolecular charge transfer (ICT) characteristics of typical nonlinear optical materials. A better ICT property of F2 is obtained by replacing terminal electron donors with stronger electron-donating ability. The degree of ICT is effectively increased, which can be clearly seen from the frontier molecular orbitals contribution of central anthracene between HOMO and LUMO. The central group plays a major role in the direction as well as effective path of ICT process. In the X-shaped oligomers with anthracene as central group, ICT process takes place from terminal groups of [Formula: see text] position branches, to the central anthracene group. However, the electron distribution as well as the ICT of tri-branched oligomer F3 with triazine as central group is not symmetric. ICT process of F3 takes place from terminal triphenylamine groups to the central triazine and two fluorene groups at [Formula: see text] position branches. Y-shaped oligomer F3 has a longer lifetime of ICT state as well as a higher fluorescence quantum yield, which is consistent with the results of time-resolved fluorescence spectroscopy. Z-scan results show that the TPA cross-section value of F3 is 10.6 and 2.9 times higher than that of X-shaped F1 and F2. The dynamics curves of transient absorption spectroscopy also indicate that oligomer F3 structure has relatively stronger ICT properties. To verify the substituent effect, two linear molecules F4 and F5 were also calculated. The quantum chemical calculations result shows that the branches at positions 4 and 11 of the central anthracene group have little effect on the electron cloud distribution, and there are indeed significant differences in the contributions of branches at different positions. Our results may provide some reference for molecular design.