Pair Charge Transfer Research Articles

Aminobenzaldehyde convelently modified graphitic carbon nitride photocatalyst through Schiff base reaction: Regulating electronic structure and improving visible-light-driven photocatalytic activity for moxifloxacin degradation.

Graphitic carbon nitride (GCN) has been demonstrated to be a potential visible-light-driven photocatalyst for eliminating organic pollutants. However, its practical application is limited by low photocatalytic efficiency originating from high recombination of photogenerated charges. In this work, the electronic structure of GCN was regulated by doping aminobenzaldehyde (ABA) into the skeleton through a solid-state Schiff base reaction. Photoelectrochemical characterizations illustrated that the obtained catalyst (CNABA) exhibited narrower band gap, lower recombination rate of photoinduced electron-hole pair and higher charge transfer ability than the pristine GCN, further indicating its excellent photocatalytic activity. Using moxifloxacin (MOX) as a model pollutant, the ABA doping content was firstly optimized and the optimal activity of the CNABA photocatalyst was 3.1 times higher than that of the GCN. Subsequently, the effects of pH value, photocatalyst dosage and MOX concentration on the photocatalytic behavior were also studied. Superior stability and photocatalytic reusability were confirmed by five repeated tests. By substituting tap water/natural lake water for deionized water and sunlight for xenon light, the CNABA also exhibited high elimination efficiency, implying its good practicability. Superoxide radical, hydroxyl radical and photogenerated hole were identified as the main active species to degrade MOX. Finally, possible degradation pathways for MOX to mineralize small molecules were proposed by determining intermediate products during photocatalysis. This work provides a solid-state method to rationally design aromatic system-modified GCN photocatalysts, and the obtained CNABA is a promising visible-light-driven photocatalyst for eliminating antibiotics.

Multi-heteroatom-doping promotes molecular oxygen activation on polymeric carbon nitride for simultaneous generation of H2O2 and degradation of oxcarbazepine.

Simultaneously realizing the efficient generation of H2O2 and degradation of pollutants is of great significance for environmental remediation. However, most polymeric semiconductors only show moderate performance in molecular oxygen (O2) activation due to the sluggish electron-hole pair dissociation and charge transfer dynamics. Herein, we develop a simple thermal shrinkage strategy to construct multi-heteroatom-doped polymeric carbon nitride (K, P, O-CNx). The resultant K, P, O-CNx not only improves the separation efficiency of charge carriers, but also improves the adsorption/activation capacity of O2. K, P, O-CNx significantly increases the production of H2O2 and the degradation activity of oxcarbazepine (OXC) under visible light. K, P, O-CN5 shows a high H2O2 production rate (1858 μM h-1 g-1) in water under visible light, far surpassing that of pure PCN. The apparent rate constant for OXC degradation by K, P, O-CN5 increases to 0.0491 min-1, which is 8.47 times that of PCN. Density functional theory (DFT) calculations show that the adsorption energy of O2 near phosphorus atoms in K, P, O-CNx is the highest. This work provides a new idea for the efficient degradation of pollutants and generation of H2O2 at the same time.

Simple hydrothermal preparation of sulfur fluoride-doped g-C3N4 and its photocatalytic degradation of methyl orange

By doping F and S elements, a graphite phase carbon nitride (g-C3N4) photocatalyst with exfoliated layers, namely, sulfur fluoride-doped carbon nitride (F-SCN), was successfully synthesized, which can effectively photocatalyze the degradation of methyl orange (MO). Based on the effect of different fluorination ratios on the degradation efficiency of MO, the optimal fluorination modification conditions of the material were obtained. It was found that doping with F and S elements significantly enhanced the electron-hole pair separation ability and charge transfer efficiency of the g-C3N4 photocatalyst, thus improving the photocatalytic performance. The results of the photocatalytic experiment show that the degradation rate of MO by F-SCN reached 62 % in 1 h, which was 3.7 and 1.4 times that of BCN and SCN, respectively, and the removal rate reached 77 % in 1 h, which was 3.8 times the rate of BCN and 1.6 times the rate of SCN.

Levofloxacin degradation under visible-LED photo-catalyzing by a novel ternary Fe–ZnO/WO3 nanocomposite

As semiconductor photocatalysts showing their efficient redox ability upon illumination, new development of materials to enhance the pollution degradation is gaining popularity, especially on their oxidation ability. In this study, a highly stable ternary Fe–ZnO/WO3 nanocomposite photocatalyst has been synthesized in order to improve charge transfer of photocatalytic oxidation under 30W LED light (425–470 nm) to efficiency degrade the Levofloxacin (LVF) in the solution. This catalyst was characterized and analyzed by XRD, FE-SEM, HR-TEM, X-ray XPS, UPS, PL, TRPL, LSV, EIS, and Photocurrent. Various important factors for the photodegradation were investigated, including Fe content, initial LVF concentration, catalyst dosage, and solution pH. The optimal conditions were Fe 1.0 wt%, LVF 10 mg L−1, Fe–ZnO/WO3 dosage 0.5 g L−1, and pH 7 for LVF photodegradation up to 96% with a kinetic rate constant of 0.0342 min−1 and were stable in photodegradation efficiency (90%) after five test cycles. In the visible LED light, the activation bandgap was estimated to be 2.75 eV with high electron-hole pair separation and charge transfer from Fe–ZnO to WO3 that could enhance the generation of active species of •OH. Moreover, the more effective charge separation of Fe–ZnO/WO3 were confirmed by lower PL intensity and longer charge carrier lifetime. Fe–ZnO/WO3 also demonstrated the excellent electrochemical properties with high photocurrent and small resistance. For the LVF degradation, 3 possible pathways were proposed with 12 intermediate products. This study demonstrated that the synthesized Fe–ZnO/WO3 could serve as a reliable visible-light responsive photocatalysts with the potential for degrading antibiotics in solution.

Visible light-induced synthesis of (Z)-β-iodoenamides from N-vinyl amides mediated by the ion pair charge transfer state

A facile and novel approach for the highly chemo- and stereoselective synthesis of (Z)-β-iodoenamides from N-vinyl amides has been developed based on a visible-light-induced ion pair charge transfer state derived from pyridinium iodides.

Self‐Assembled Metal–Organic Framework Stabilized Organic Cocrystals for Biological Phototherapy

AbstractOrganic self‐assembled co‐crystals have garnered considerable attention due to their facile synthesis and intriguing properties, but supramolecular interactions restrict their stability in aqueous solution, which is especially important for biological applications. Herein, we report on the first biological application of aqueous dispersible self‐assembled organic co‐crystals via the construction of metal–organic framework (MOF) ‐stabilized co‐crystals. In particular, we built an electron‐deficient MOF with naphthalene diimide (NDI) as the ligand and biocompatible Ca2+ as the metal nodes. An electron donor molecule, pyrene, was encapsulated to form the host–guest MOF self‐assembled co‐crystal. We observed that such MOF structure leads to uniquely high‐density ordered arrangement and the close intermolecular distance (3.47 Å) of the charge transfer pairs. Hence, the concomitant superior charge transfer interaction between pyrene/NDI can be attained and the resultant photothermal conversion efficiency of Py@Ca‐NDI in aqueous solution can thus reach up to 41.8 %, which, to the best of our knowledge, is the highest value among the reported organic co‐crystal materials; it is also much higher than that of the FDA approved photothermal agent ICG as well as most of the reported MOFs. Based on this realization, as a proof of concept, we demonstrated that such a self‐assembled organic co‐crystal platform can be used in biological applications that are exemplified via highly effective long wavelength light photothermal therapy.

Self-Assembled Metal-Organic Framework Stabilized Organic Cocrystals for Biological Phototherapy.

Organic self-assembled co-crystals have garnered considerable attention due to their facile synthesis and intriguing properties, but supramolecular interactions restrict their stability in aqueous solution, which is especially important for biological applications. Herein, we report on the first biological application of aqueous dispersible self-assembled organic co-crystals via the construction of metal-organic framework (MOF) -stabilized co-crystals. In particular, we built an electron-deficient MOF with naphthalene diimide (NDI) as the ligand and biocompatible Ca2+ as the metal nodes. An electron donor molecule, pyrene, was encapsulated to form the host-guest MOF self-assembled co-crystal. We observed that such MOF structure leads to uniquely high-density ordered arrangement and the close intermolecular distance (3.47 Å) of the charge transfer pairs. Hence, the concomitant superior charge transfer interaction between pyrene/NDI can be attained and the resultant photothermal conversion efficiency of Py@Ca-NDI in aqueous solution can thus reach up to 41.8 %, which, to the best of our knowledge, is the highest value among the reported organic co-crystal materials; it is also much higher than that of the FDA approved photothermal agent ICG as well as most of the reported MOFs. Based on this realization, as a proof of concept, we demonstrated that such a self-assembled organic co-crystal platform can be used in biological applications that are exemplified via highly effective long wavelength light photothermal therapy.

Tailoring the properties of g-C3N4 with CuO for enhanced photoelectrocatalytic CO2 reduction to methanol

In the present work, the physico-chemical and photoelectrocatalytic (PEC) carbon dioxide (CO2) reduction to methanol properties of graphitic carbon nitride (g-C3N4) were enhanced by the incorporation of CuO. The XRD, XPS, TEM, FESEM, UV–vis and photoluminescence (PL) spectroscopy techniques were used to characterize the synthesized g-C3N4 and CuO/g-C3N4 photocatalysts. The fabricated CuO/g-C3N4/carbon paper photocathode showed ∼10.0 times enhanced photocurrent response and 5.3 times enhanced incident photon to current efficiency (IPCE) than the g-C3N4/carbon paper photocathode under CO2 atmosphere in aqueous NaHCO3 electrolyte solution on 470 nm light irradiation. The higher IPCE of CuO/g-C3N4/carbon paper photocathode was attributed to the higher absorption of the incident visible light which results in efficient electron (e−-hole (h+) pair generation and charge transfer for the PEC conversion of CO2. The production of methanol in aqueous phases was analysed and found to be 4.1 and 2.6 times higher by CuO/g-C3N4/carbon paper photocathode than g-C3N4/carbon paper and CuO/carbon paper photocathodes, respectively. The CuO/g-C3N4/carbon paper photocathode showed Faradaic efficiency and quantum efficiency of 75 % and 8.9 %, respectively for the production of methanol. The plausible mechanism for the production of methanol by CuO/g-C3N4/carbon paper photocathode by PEC reaction was also discussed.

In situ constructing intramolecular ternary homojunction of carbon nitride for efficient photoinduced molecular oxygen activation and hydrogen evolution

Abstract Polymeric semiconductors potentially rich in Frenkel excitons are booming in photocatalysis, but most of them only show moderate performance in hydrogen evolution and molecular oxygen activation due to the sluggish electron−hole pair dissociation and charge transfer dynamics. Herein, a novel design of intramolecular g–C3N4–based ternary homojunction is established via one step KSCN/NH4Cl-assisted ionothermal route. The integrated theoretical calculations and experimental results disclose that such a unique ternary structure not only dramatically expedite intralayer exciton splitting and interface charge transfer but also greatly reduce backward charge recombination through the arrangement of HOMO/LUMO levels and consequent internal electric field. As a result, the optimal sample exhibits remarkable enhancements in oxygen (O2) reduction to hydroxyl radicals (•OH), and water splitting with H2 evolution rate (3806.5 μmol h−1 g−1) about 17.8 times higher than that of unmodified melon outperforming most functionalized g-C3N4 and heterojunctions reported thus far. Our study highlights the rational design of chemical structures to modulate the excitonic features and charge-transfer properties of polymeric semiconductors for efficient solar energy utilization.

Ion-Pair Formation of [CoIII(pn)2(Cl)(L)2+····· I−] by Aqueous-Organic Solvent Medium Enhanced Photoreduction: A Perspective Regression Analysis

Reduction of CoIII centre in CoIII(pn)2(Cl)(L)2+ with reference to solvent medium and structure of the complex via ion pair charge transfer (IPCT) paves way for the novel reaction mechanism route. In this work, we prepared, characterized and photoinduced the complexes CoIII(pn)2(Cl)(L)2+ (where L = RC6H4NH2, R = m-OMe, p-F and H) in the presence of iodide ion. Quantum yield for 254 nm excitation of CoIII(pn)2(Cl)(L)2+(where L = RC6H4NH2, R = m-OMe, p-F and H) in water-1,4-dioxane mixtures (Diox = 0, 5, 10, 15, 20, 25, and 30% (v/v)) were also derived for all the complexes in presence of added iodide ion, in which CoIII was reduced via [CoIII(pn)2(Cl)(L)2+….. I-] ion-pair formation. The photoinduced state is ion-pair charge transfer transition state and the quantum efficiency is solvent reliant and they are non-reactive. That is, change in ΦCo(II) is dependable with observed increase in xDiox of the mixed solvent medium. Correlation analysis using empirical parameters εr, Y, ET N and DNN provides a model to understand the solvent medium participation and interaction. This work gains an insight into the role of aqueous-organic solvent medium in CoIII(pn)2(Cl)(L)2+ photoreduction, which may be of great significance in developing novel approaches in the field of high performance catalysis

Comparative studies on the effect of CB[8] on the charge transfer interaction

Cucurbit[8]uril (CB[8])-stabilized charge transfer pair between 2, 6-dihydroxynaphthalene and methylviologen derivative has been theoretically studied at the PBE0-D3/6-311+G* level. The structure, interaction energy, electron density, and frontier orbital properties of the complex inside CB[8] have been computed and compared with the corresponding properties in gas and water at the same level. Geometric and energetic results show that the guest pair inside CB[8] represents closer packing and stronger binding energy. The VMD program makes the binding strength visible, and the results are consistent with the binding energy results in gas, water, and CB[8]. The results of charge transfer excitation analysis suggest that CB[8] weakens the effect of solvation on the charge transfer excitation to make the complex show a charge transfer character. The calculation results of HOMO and LUMO orbitals suggest that the cavity of the CB[8] is helpful for the intermolecular charge transfer when compared with the case in water and is not involved in this process. This investigation would be useful for our understanding on the function of CB[8] and helpful in designing the supramolecular systems.

Strong ion pair charge transfer interaction of 1,8-naphthalimide–bipyridinium conjugates with basic anions – towards the development of a new type of turn-on fluorescent anion sensors

Fluoride, acetate and benzoate anions reduce naphthalimide–viologen dyads into radicals, which is indicated by a strong fluorescence enhancement.

Designing Hybrids of Graphene Oxide and Gold Nanoparticles for Nonlinear Optical Response

Nonlinear optical absorption of light by materials are weak due to its perturbative nature, although a strong nonlinear response is of crucial importance to applications in optical limiting and switching. Here we demonstrate experimentally and theoretically an extremely efficient scheme of excited state absorption by charge transfer between donor and acceptor materials as the new method to enhance the nonlinear absorption by orders of magnitude. With this idea, we have demonstrated strong excited state absorption (ESA) in reduced graphene oxide that otherwise shows increased transparency at high fluence and enhancement of ESA by one orders of magnitude in graphene oxide by attaching gold nanoparticles (AuNP) in the tandem configuration that acts as an efficient charge transfer pair when excited at the plasmonic wavelength. To explain the unprecedented enhancement, we have developed a five-level rate equation model based on the charge transfer between the two materials and numerically simulated the results. To understand the correlation of interfacial charge-transfer with the concentration and type of the functional ligands attached to the graphene oxide sheet, we have investigated the AuNP-graphene oxide interface with various possible ligand configurations from first-principles calculations. By using the strong ESA of our hybrid materials, we have fabricated liquid cell-based high-performance optical limiters with important device parameters better than that of the benchmark optical limiters.

First Principles Probing of Photo-Generated Intermolecular Charge Transfer State in Conjugated Oligomers

We perform density functional theory calculations to investigate the polaron pair (charge transfer state) photo-generation in donor-acceptor oligomer methyl-capped (4,7-benzo[2,1,3]thiadiazole-2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[1,2-b;3,4-b′]dithiophene-4, 7-benzo[2,1,3]thiadiazole) (CPDTBT). Results show that effective photo-generation of charge transfer state can happen in CPDTBT dimer when the group 4,7-benzo[2,1,3]thiadiazole (BT) in one monomer deviates against the conjugated plane (onset torsion angle is about 20°). The lower excitation energy (530 nm) can only generate the intramolecular excitonic state, while the higher excitation energy (370 nm) can generate the intermolecular charge transfer state, in good agreement with the experiment. Moreover, the mechanism of charge separation in CPDTBT oligomers is discussed.

Ternary Bismuthide SrPtBi2: Computation and Experiment in Synergism to Explore Solid-State Materials

A combination of theoretical calculation and the experimental synthesis to explore the new ternary compound is demonstrated in the Sr-Pt-Bi system. Since Pt-Bi is considered as a new critical charge-transfer pair for superconductivity, it inspired us to investigate the Sr-Pt-Bi system. With a thorough calculation of all the known stable/metastable compounds in the Sr-Pt-Bi system and crystal structure predictions, the thermodynamic stability of hypothetical stoichiometry, SrPtBi2, is determined. Followed by the high-temperature synthesis and crystallographic analysis, the first ternary bismuthide in Sr-Pt-Bi, SrPtBi2 was prepared and the stoichiometry was confirmed experimentally. SrPtBi2 crystallizes in the space group Pnma (S.G. 62, Pearson Symbol oP48), which matches well with theoretical prediction using an adaptive genetic algorithm (AGA). Using first-principles calculations, we demonstrate that the orthorhombic structure has lower formation energies than other 112 structure types, such as tetragonal BaMnBi2 (CuSmP2) and LaAuBi2 (CuHfSi2) structure types. The bonding analysis indicates the Pt-Bi interactions play a critical role in structural stability. The physical properties measurements show the metallic properties with low electron-phonon interactions at the low temperature, which agrees with the electronic structure assessment.

Tunable two-dimensional interfacial coupling in molecular heterostructures

Two-dimensional van der Waals heterostructures are of considerable interest for the next generation nanoelectronics because of their unique interlayer coupling and optoelectronic properties. Here, we report a modified Langmuir–Blodgett method to organize two-dimensional molecular charge transfer crystals into arbitrarily and vertically stacked heterostructures, consisting of bis(ethylenedithio)tetrathiafulvalene (BEDT–TTF)/C60 and poly(3-dodecylthiophene-2,5-diyl) (P3DDT)/C60 nanosheets. A strong and anisotropic interfacial coupling between the charge transfer pairs is demonstrated. The van der Waals heterostructures exhibit pressure dependent sensitivity with a high piezoresistance coefficient of −4.4 × 10−6 Pa−1, and conductance and capacitance tunable by external stimuli (ferroelectric field and magnetic field). Density functional theory calculations confirm charge transfer between the n-orbitals of the S atoms in BEDT–TTF of the BEDT–TTF/C60 layer and the π* orbitals of C atoms in C60 of the P3DDT/C60 layer contribute to the inter-complex CT. The two-dimensional molecular van der Waals heterostructures with tunable optical–electronic–magnetic coupling properties are promising for flexible electronic applications.

Optical, magnetic and thermal properties of colloidal suspension of ferrofluids synthesized by laser ablation

A high power Nd: YAG laser has been employed to produce magnetic colloids (ferrofluids) of iron oxide nanoparticles (NPs) in double distilled water. It is found that FeO (Wüstite) phase of iron oxide has been produced as an initial product; after oxidation and agglomeration it appears as Fe2O3 a stable composition of iron oxide. UV–visible absorption spectroscopy has been employed to distinguish both phases of iron oxide NPs. Absorption band gap of as synthesized ferrofluids at different pulse energies (30, 40, 50, 60 mJ) has been calculated. The absorption band gap of as synthesized FeO magnetic colloids is found in the range of (2.91–3.13 eV) and (3.37–3.91 eV) respectively which arises due to pair excitation and charge transfer. Absorption band gaps of Fe2O3 are found in the range of (2.16–2.28 eV) and (2.68–3.10 eV) respectively again due to pair excitation and charge transfer. Magnetic measurement was performed using VSM which confirms antiferromagnetic nature of FeO NPs with coercivity 47 Oe and magnetic domain size 73.50 Å at 300 K. Zero field cooled and field cooled magnetization confirms blocking and Néel temperature 245 ± 2 K and 181 ± 2 K respectively.Highlight for review1. As synthesized colloidal suspension of iron oxide NPs can be used as efficient cooling agent.2. FeO composition of iron oxide has been synthesized using PLA3. Optical band gap of colloidal suspension of iron oxide NPs is calculated at different laser energy.4. Magnetic properties of iron oxide NPs have been studied.

The S···P noncovalent interaction: diverse chalcogen bonds

ABSTRACTThe S···P interactions in the complexes of HSX (X = F, Cl, Br, I) with PHnMe3-n(n = 0–3) have been investigated with ab initio calculations at the MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ level of theory. The interaction energies and structural properties of intermolecular complexes have been analyzed. Results of QTAIM analysis are dealing with expand of interactions, including pure closed-shell interactions (van der Waals interactions and chalcogen bonding, YB), partially covalent closed-shell (CS; Charge Transfer) and shared-shell interactions (SS; weak covalent bond and very strong YB) for these complexes. The energy decomposition analysis (EDA) showed that electrostatic interactions are an important contributing factor for these complexes. In considering second-order contributions, the donor-acceptor pair charge transfer (CT) is most important. These findings are consistent with the Electron Localization Function (ELF) isosurface of the complexes. In each series of HXS:PHnMe3-n-chalcogen bond complexes with increasing basicity of phosphines, the stability and S···P bond strength of adducts were increased so that the HXS:PMe3 (X = F, Cl, Br) complexes had very strong S···P chalcogen interactions with nearly covalent characters.

Examination of tryptamine-squaraine complexes as both colorimetric and fluorometric stains in gel electrophoresis

Abstract A water-soluble dual pendent squaraine with tryptaminium cations has been mixed with mono-nitroaromatics in solution to create ternary complexes with the aim of creating indole-nitroaromatic charge-transfer pairs. Examination of the X-ray crystal structures of two tryptamine-nitroaromatic complexes, without the squaraine moiety, revealed that neither demonstrated charge-transfer pair or stacking associations between the indole and nitroaromatic rings. Examination of the fluorescence performance upon illumination with 300 nm light of each ternary squaraine complex, particularly in the presence of an equimolar amount of protein, showed that the levels across the series were no more than that observed for the base bis-tryptaminium squaraine, as was observed in a previous study. However, electrophoresis gels stained with the base bis-tryptaminium squaraine, whose X-ray crystal structure is also reported, were found to fluorescence; the only other squaraine dye of this type to do so in addition to the bis-piperidinium squaraine of previous studies.

(Invited) Insights into Solvation, Dynamics and Stability of Electrolytes for the Design of Novel Multivalent Systems from Coupled Molecular Dynamics and First-Principles Modeling

Within the Joint Center for Energy Storage (JCESR) we have developed a high-throughput infrastructure for the automated calculation of molecular properties with a focus on battery electrolytes. Computational screening techniques have been found to be an effective alternative to the trial and error of experimentation for discovery of new materials. Using this infrastructure, we have computed the ionization potential (IP) and electron affinities (EA) of 16,000 molecules relevant to electrolytes targeting both multivalent intercalation as well as non-aqueous redox flow systems. For some potential multi-valent electrolytes we use classical molecular dynamics simulations coupled with ab initio calculations for Mg salts in various solvents. We uncover a novel effect between concentration dependent ion pair formation and anion stability at reducing potential, e.g., at the metal anode1. We elucidate systematic correlations between molecular level interactions and composite electrolyte properties, such as electrochemical stability, solvation structure, and dynamics. Specifically, we find that multivalent electrolytes are highly prone to ion pair formation, even at modest concentrations, for a wide range of solvents with different dielectric constants, which have implications for dynamics as well as charge transfer. For example, at Mg metal potentials, the ion pair undergoes partial reduction at the Mg cation center (Mg2+→Mg+), which competes with the charge transfer mechanism and can activate the anion to render it susceptible to decomposition. Specifically, TFSI− exhibits a significant bond weakening while paired with the transient, partially reduced Mg+. This information provides critical design metrics for future electrolytes as it elucidates a close connection between bulk solvation and cathodic stability as well as the dynamics of the salt. We use our previous insights to design for new Mg electrolyte anions with the aim to stabilize the electrolyte during possible ion pair formation and charge transfer reactions. Through comprehensive calculations using both first-principles as well as well-benchmarked classical molecular dynamics, we proposed 16 new electrolyte salts. Based on successive property evaluation such as electrochemical stability window, chemical decomposition and hydrolysis vulnerability we down-select 4 potential new anions for Mg electrolytes.