Lewis Acid-base Chemistry Research Articles

Substituent engineering in tertiary phosphine oxides for passivating defects of perovskite solar cells

AbstractDefect passivation based on Lewis acid–base chemistry has been regarded as an effective strategy to improve the photovoltaic performance and stability of perovskite solar cells (PSCs). Here, we report on tertiary phosphine oxides (R3PO) as materials for defect passivation, where photovoltaic performance was investigated depending on the substituents R. Electron‐donating ability of the substituents in R3PO was found to play an important role in passivation. Cyclohexyl substituent was better in achieving photovoltaic performance than linear hexyl substituent. The heterocyclic morpholine substituent bearing oxygen and nitrogen in cyclohexyl form further improved photovoltaic performance due to its enhanced electron‐donating ability. Compared with an untreated PSC, the trimorpholinophosphine oxide (TMPPO)‐treated PSC improved the power conversion efficiency from 21.95% to 23.72%. Additionally, the dark‐storage stability test with an unencapsulated device showed that the TMPPO‐treated device maintained 92.7% of its initial PCE after 1250 h, while 86.8% was maintained for the untreated device. Three hundred hour‐light‐soaking of the encapsulated devices revealed that the operational stability of the TMPPO‐treated PSC was superior to the untreated device.image

2-Alkylphosphino-1-boraadamantanes.

Boraadamantanes are a privileged class of caged group 13 compounds having a trigonal pyramidal (non-VSEPR) ground-state. The Lewis acid-base chemistry of this type of compound is underdeveloped when compared to acyclic derivatives. This report provides the first examples of bifunctional boraadamantanes with an appended phosphine moiety (also the first boraadamantanes having a phosphorus-boron bond). Using this scaffold, boraadamantane coordination compounds are accessed for the first time.

A novel solvent system of polyamides achieves new application in ZIBs by aggregation induced Lewis acid-base centers

Dissolutions of the polymer in the chaotropic salts follow Hofmeister effect, and the aggregate of salts and solvents shows new influence of the Hofmeister effect. Here, we reveal the aggregation of ion–solvent in chaotropic salt solution catalyzes the formation of the exposed Lewis acid-base center and realizes the dissolution of polyamide (PA) macromolecules. The relationship between Hofmeister effect, aggregate chemistry and Lewis acid-base chemistry is examined from new perspective. And then, a new solvent system and phase conversion process are designed for polyamides. Finally, the applications of PA in ZIBs as coating layer and binder are realized. As an electrode coating, it can effectively inhibit hydrogen evolution, corrosion and dendrite problems and improve the cycle life (cycle over 1500 h at 0.5 mA cm−2). As a binder, the active material adhesion on current collector, uniformity and wettability of the electrode are improved. The assembled pouch-cell with PANI cathode shows a capacity of 150 mAh g−1 after 120 cycles. This work reveals the secret of controlled phase transformation of polyamide in saline solution from a new perspective. And this phase conversion method is simpler, greener and more environmentally friendly, which greatly accelerates the application of polyamide in the field of membrane science and binder science.

Porous carbon supported Lewis acid-base sites as metal-free catalysts for the carbonylation of glycerol with urea

Glycerol carbonylation is one of the most efficient reaction pathways to utilize glycerol, one of the by-products in biodiesel industry. So far, the vast majority of the reported glycerol carbonylation catalysts contain metals, which are not environmentally friendly. The recent emerging Lewis acid-base chemistry had provided powerful alternatives for metal-free catalysis. Here, we report the facile preparation of the B,N,P co-doped porous carbon materials, and the Lewis acidic/basic defects were detected in their structures. The obtained material BNP@C-800 exhibits excellent catalytic performance for the catalytic carbonylation of glycerol with urea, which achieved up to 93.6% glycerol conversion and 93.7% glycerol carbonate selectivity under metal-free conditions. The catalyst BNP@C-800 could be easily recycled for five times only by simple treatments without obvious loss in catalytic activity. In addition, the key reaction intermediate glycerol urethane was successfully characterized via React-IR spectroscopy. Furthermore, a heterogeneous Lewis acid-base synergistic catalysis mechanism is proposed.

Rational Selection of the Lewis Base Molecules Targeted for Lead-Based Defects of Perovskite Solar Cells: The Synergetic Co-passivation of Carbonyl and Carboxyl Groups.

Defect passivation through Lewis acid-base chemistry has recently attracted significant interest because of its proven ability to improve the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). However, tedious trial-and-error procedures are commonly used for the selection of Lewis molecules due to their abundant variety. Herein, two typical Lewis base molecules, the M molecule containing only carbonyl groups and the 3M molecule containing both carbonyl and carboxyl groups, are proposed to passivate the Pb-based defects and mitigate their negative impacts on PSC performance. The results indicated that much stronger coordination bonds can be formed between the 3M molecule and uncoordinated Pb2+ than with the M molecule. Because of the benefit from the synergetic co-passivation effect of carbonyl and carboxyl groups, an impressive maximum PCE of 24.07% was achieved via 3M modification. More importantly, the modified devices demonstrated remarkably improved operational stability.

Efficient molecular ferroelectric photovoltaic device with high photocurrent via lewis acid–base adduct approach

Traditional inorganic oxide ferroelectric materials usually have band gaps above 3 eV, leading to more than 80% of the solar spectrum unavailable, greatly limiting the current density of their devices just at μA cm−2 level. Therefore, exploring ferroelectric materials with lower band gaps is considered as an effective method to improve the performance of ferroelectric photovoltaic devices. Inorganic ferroelectric materials are often doped with transition metal elements to reduce the band gap, which is a complex doping and high temperature fabrication process. Recently, molecular ferroelectric materials can change the symmetry and specific interactions of crystals at the molecular level by chemically modifying or tailoring cations with high symmetry, enabling rational design and banding of ferroelectricity in the framework of perovskite simultaneously. Therefore, the molecular ferroelectric materials have a great performance for both excellent ferroelectricity and narrow band gap without doping. Here, we report a ferroelectric photovoltaic device employing an organic-inorganic hybrid molecular ferroelectric material with a band gap of 2.3 eV to obtain high current density. While the poor film quality of molecular ferroelectrics still limits it. The Lewis acid–base adduct is found to greatly improve the film quality with lower defect density and higher carrier mobility. Under standard AM 1.5 G illumination, the photocurrents of ∼1.51 mA cm−2 is achieved along with a device efficiency of 0.45%. This work demonstrates new possibilities for the application of molecular ferroelectric films with narrow band gaps in photovoltaic devices, and lays a foundation for Lewis acid–base chemistry to improve the quality of molecular ferroelectric thin films to obtain high current densities and device performance.

Post-synthesis from Lewis acid-base interaction: an alternative way to generate light and harvest triplet excitons.

The changes in absorption and emission of fluorescent materials with the introduction of Lewis acids have been frequently observed due to either physical or chemical interactions. In this mini-review, we elaborate how Lewis acids adjust the optical properties and the bandgap of luminescent materials by simple coordination reactions. It is common that fluorescent materials containing Lewis basic nitrogen heterocycles are more likely to provide the feasible band gap modulation. The essence of such phenomenon originates from Lewis acid–base coordination and adducts, which highly depends on the electron-accepting property of the Lewis acids. This intermolecular mechanism, considered as post-synthesis of new luminescent compounds offers promising applications in sensing and electroluminescence by manipulating the frontier molecular orbital energy levels of organic conjugated materials, simply based on Lewis acid–base chemistry.

Can Brønsted Photobases Act as Lewis Photobases?

Dative bonding or Lewis acid-base chemistry underpins a large number of chemical phenomena in a variety of fields, such as catalysis, metal-ligand interactions, and surface chemistry. Developing light-controlled Lewis acid-base interactions could offer a new way of controlling and understanding such phenomena. Photoinduced proton transfer, that is, excited-state Brønsted acidity and basicity, has been extensively studied and applied. Here, in direct analogy to excited-state Brønsted basicity, we show that exciting a photobasic molecule with light generates a thermodynamic drive for the transfer of a Lewis acid from a donor to a photobasic molecule. We have used the archetypal BF3 as our Lewis acid and our photoactive Lewis bases are a family of quinolines, which are known Brønsted photobases as well. We have constructed the experimental Förster cycle for this system and have verified it computationally to demonstrate that a significant drive (0.2-0.7 eV) exists for the transfer of BF3 to a photoexcited quinoline. The magnitude of this drive is similar to those reported for Brønsted photobasicity in quinolines. Computational results from TDDFT and energy decomposition analysis show that the origin of such an effect is similar to the Brønsted photoactivity of these molecules, in that they follow the Hammett parameter of substituent groups. These results suggest that photobases may be capable of controlling the chemical phenomena beyond proton transfer and may open opportunities for a new handle in photocatalysis.

Fluorescent Organic Lewis-Pair Nanoparticles: Excited-State Intramolecular Proton Transfer Molecule 2-(2'-Hydroxyphenyl)benzothiazole Undergoes GSIPT Reactions To Be a Solid-State Nanoemitter.

The excited-state intramolecular proton transfer (ESIPT) reaction, one of the fundamental photochemical processes, is known to occur in 2-(2'-hydroxyphenyl)benzothiazole (HBT), showing an enol-to-keto phototautomerization. In this article, Lewis-pair adduct formation is demonstrated between HBT (Lewis base) and diphenylborinic anhydride (DPBA; Lewis acid), in which the proton transfer occurs in the ground state to form the keto tautomer of HBT. The HBT/DPBA Lewis-pair adduct exhibits strong pale-blue fluorescence at 480 nm in dichloroethane. Additionally, organic Lewis-pair nanoparticles of HBT/DPBA are successfully synthesized on the basis of a reprecipitation protocol in which HBT in conjunction with DPBA dissolved in acetone was rapidly injected into water under ultrasonication. DPBA here also acts as a stabilizing or protecting agent to form spherical nanoparticles with well dispersion. The nanoparticles also exhibit strong keto-type emission centered at 490 nm, changing the emission color to bluish-green. Quantum chemical calculations find the sole formation of the keto tautomer of HBT counterpart in the Lewis pair. Importantly, the present synthesis methodology based on Lewis acid-base chemistry does not require complicated operations to organically synthesize solid-state emitters and thus will play a key role in simply controlling the emission behavior for the new type of organic nanoparticles.

Tailored graphene quantum dots to passivate defects and accelerate charge extraction for all-inorganic CsPbIBr2 perovskite solar cells

Graphene quantum dots (GQDs) have shown great potential to simultaneously improve the stability and efficiency of perovskite solar cells (PSCs). However, their preparation is either extremely harsh or inefficient, which severely hampers the extensive research and application. Herein, a novel solid-liquid interfacial exfoliation technique is established to fabricate high-quality GQDs from carbon fiber, in which the throughput of GQDs is up to 20 g in one pot with yield over 90%. To explore their role in PSC, nitrogen and sulfur functionalized GQDs have been further synthesized via a hydrothermal method, and used to regulate the interfacial properties of all-inorganic CsPbIBr2 PSC. Arising from the interaction based on Lewis acid-base chemistry between GQDs and the under-coordinated Pb2+, the detrimental non-radiative recombination is significantly reduced, especially for the functionalized GQDs tailored PSC, leading to the champion efficiency of 9.80% for carbon-electrode based CsPbIBr2 PSCs with excellent long-term stability.

Theoretical study of the adsorption of Lewis acids on MoS2 in relation to atomic layer deposition of Al2O3

There is presently a critical need for a viable approach to form ultrathin, high-quality layers of oxides such as Al2O3 on MoS2 and related two-dimensional transition-metal chalcogenides. Atomic layer deposition (ALD), which is, in principle, the most suitable technique, has been problematic in this case as a result of the low reactivity of these substrates when free of strain, impurities, and defects. Lewis acid-base chemistry provides a possible solution, and the present work employs ab initio theory to examine the feasibility of adsorbing strongly Lewis-acidic Al reagents on MoS2. The investigation focuses on small Al precursor molecules that are able to adsorb at high coverages and, therefore, to produce a dense and uniform layer of Al(OH)3 when reacted with H2O, which is highly desirable for initiating ALD growth. Of those species considered, it is found that Al(CH3)3, the most widely used reagent for ALD of Al2O3, is actually the least favorable in terms of its interaction with the MoS2 basal plane. Other, more Lewis-acidic reagents are found to adsorb somewhat more strongly in the critical first step of the growth process and, therefore, to be potentially more useful for initiating ALD growth. The coverage dependence of the adsorption energy and geometry and the effects of AlX3 polymerization are also considered, and practical suggestions are given for how such species can be incorporated into an ALD process.

Nondestructive functionalization of monolayer black phosphorus using Lewis acids: A first-principles study

Functionalization of layered black phosphorus is valuable for engineering its chemical properties and enhancing the chemical stability. Here we report density functional theory calculations, through which we show that the phosphorus surface can be decorated by a few Lewis acids with stable interfacial binding, which preserves the band gap of monolayer black phosphorus with tunable band edge energies. The strong interfacial binding is mediated by a Lewis acid-base chemistry between the lone pair electrons in phosphorous and the electron accepting Lewis acids. We further show that magnetic moment can be introduced into phosphorus using the Lewis acids such as FeCl3. Furthermore, the surface modification can be responsive using the acylation chemistry. Our work thus shows that the chemical stability and electronic properties of black phosphorus can be finely tuned because of its rich chemistry.

Interaction of Metal Oxido Compounds with B(C6F5)3

Lewis acid-base pair chemistry has been placed on a new level with the discovery that adduct formation between an electron donor (Lewis base) and acceptor (Lewis acid) can be inhibited by the introduction of steric demand, thus preserving the reactivity of both Lewis centers, resulting in highly unusual chemistry. Some of these highly versatile frustrated Lewis pairs (FLP) are capable of splitting a variety of small molecules, such as dihydrogen, in a heterolytic and even catalytic manner. This is in sharp contrast to classical reactions where the inert substrate must be activated by a metal-based catalyst. Very recently, research has emerged combining the two concepts, namely the formation of FLPs in which a metal compound represents the Lewis base, allowing for novel chemistry by using the heterolytic splitting power of both together with the redox reactivity of the metal. Such reactivity is not restricted to the metal center itself being a Lewis acid or base, also ancillary ligands can be used as part of the Lewis pair, still with the benefit of the redox-active metal center nearby. This Minireview is designed to highlight the novel reactions arising from the combination of metal oxido transition-metal or rare-earth-metal compounds with the Lewis acid B(C6 F5 )3 . It covers a wide area of chemistry including small molecule activation, hydrogenation and hydrosilylation catalysis, and olefin metathesis, substantiating the broad influence of the novel concept. Future goals of this young and exciting area are briefly discussed.

Analysis of the role of a writing-to-learn assignment in student understanding of organic acid–base concepts

Acid–base chemistry is a foundational topic that is taught in courses across the chemistry curriculum. Students often have difficulty distinguishing between the different theories of acid–base chemistry—Brønsted–Lowry and Lewis acid–base chemistry—and applying these two definitions correctly in unfamiliar scenarios. To help students learn these definitions and be able to apply them, an acid–base Writing-to-Learn assignment was developed and evaluated. The Writing-to-Learn assignment involved a three-step process where students constructed an initial draft in response to a writing prompt, participated in peer review, and made revisions based on peer review feedback, before submitting a final draft. This process is informed by sociocultural theory applied to writing, which states that student learning of concepts increases through engagement with their peers’ work and receiving peer feedback on their own writing. To test the efficacy of the acid–base writing assignment, an external assessment, comprised of conceptual questions related to acid–base chemistry and students’ confidence when responding to them, was administered in two groups; a treatment group who completed the Writing-to-Learn assignment, and a comparison group who completed a separate assignment. Additionally, students who completed the Writing-to-Learn assignment were interviewed about their experiences. Regression analysis revealed that students in the treatment group had a greater increase in their conceptual understanding and confidence as compared to the students in the comparison group. The results demonstrate the students could successfully write about the Brønsted–Lowry and Lewis acid–base models separately, but were less successful with connecting these two concepts together in their writing. These results demonstrate the efficacy of Writing-to-Learn as an approach for promoting conceptual learning of acid–base chemistry.

A Lewis acid-base chemistry approach towards narrow bandgap dye molecules

Although it usually involves troublesome and time-consuming synthesis work, molecular structure tailoring has been the mainstream tool to adjust the optical absorption and bandgap of organic semiconductors. Herein, we provided a convenient and feasible method to prepare narrow bandgap small-molecule semiconductors by Lewis acid-base chemistry and the optical absorption was adjusted by the stoichiometry of Lewis acid-base reactions. In this work, three pyridine capped diketopyrrolopyrrole (DPP) molecules, i.e., DPPPy-Ph-F, DPPPy-Ph-3F, and DPPPy-Py-F, with medium bandgap were synthesized to coordinate with Lewis acid of B(C6F5)3 (BCF). By coordinating with BCF, as demonstrated by 1H, 19F, and 11B NMR spectra, the bandgaps of these DPP molecules were depressed largely. For DPPPy-Ph-F, with two pyridine units flanking symmetrically, 2 eq of BCF converted the two pyridine nitrogens stoichiometrically to Lewis acid adducts, along with absorption bands red-shifted and bandgap depressed (1.89 vs. 1.80 eV). For DPPPy-Ph-3F, with two pyridine units flanked and trifluorobenzene capped, adding 2 eq of BCF was unable to convert the two pyridine nitrogens to BCF adducts completely, due to the strong electron-drawing ability of trifluorobenzene substituent on pyridine, reducing its basicity. After adding excess BCF to coordinate with nitrogens, the bandgaps of DPPPy-Ph-3F also decreased from 1.92 eV to 1.84 eV. For DPPPy-Py-F, with four pyridine units flanked, 4 eq of BCF were required to bind the pyridine nitrogens. Accordingly, the red-shift of absorption bands and the depression of optical bandgaps (1.96 vs. 1.75 eV) for DPPPy-Py-F were most striking among the three molecules.

Self-Assembled Vesicle-Carbon Nanotube Conjugate Formation through a Boronate-Diol Covalent Linkage.

A vesicle-single walled carbon nanotube (CNT) conjugate was developed by a boronic acid-diol covalent linkage between a self-assembled vesicle and dispersed CNT. Trimesic acid based phenylboronic acid appended triple-tailed amphiphiles (T1 and T1S) were synthesized that formed monolayered vesicles through H-aggregation in DMSO-water (2:1 v/v) and pure water, respectively. Aqueous CNT dispersion was prepared with cholesterol-based glucose-functionalized amphiphile (D1). These two supramolecular self-assemblies were covalently linked by using a boronic acid-diol interaction between a phenylboronic acid based T1S vesicle and 1,2-diol moieties of glucose tethered dispersing agent (D1) to develop a vesicle-CNT conjugate. Lewis acid-base chemistry was exploited to form this boronate-diol adduct between two supramolecular self-assemblies. The formation of vesicles, CNT dispersion, and the vesicle-CNT conjugate was characterized by microscopic and spectroscopic techniques. Anticancer drug doxorubicin was encapsulated within this T1S-vesicle-D1-CNT conjugate with a higher loading capacity compared to the individual cargo carrier (vesicle or CNT). This cytocompatible T1S-vesicle-D1-CNT conjugate successfully delivered loaded doxorubicin within a B16F10 melanoma cell and also exhibited better cellular transportation ability compared to the drug-loaded vesicle or CNT. This was further reflected in an enhanced killing efficiency of the cancer cells by the vesicle-CNT conjugate compared to the drug-loaded vesicle or CNT.

Surface functionalization of two-dimensional metal chalcogenides by Lewis acid-base chemistry.

Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid-base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti(4+) to form planar p-type [Ti(4+)n(InSe)] coordination complexes. Using this strategy, we fabricate planar p-n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B(3+), Al(3+) and Sn(4+)) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid-base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.

Alkylamine-functionalized hexagonal boron nitride nanoplatelets as a novel material for the reduction of friction and wear.

Hexagonal boron nitride nanoplatelets (h-BNNPs), which are structurally analogous to graphene, were prepared via the ultrasound-assisted exfoliation of h-BN powder using N-methyl pyrrolidone as the solvent. The alkylamines with variable alkyl chains and electron-rich nitrogen atoms were grafted onto the boron sites of the h-BNNPs based on Lewis acid-base chemistry. The grafting of the alkylamines onto the h-BNNPs was confirmed using FTIR, XPS, TGA and (13)C SSNMR analyses. The crystalline and structural features of the alkylamine-functionalized h-BNNPs were studied using XRD and HRTEM analyses. The TGA and FTIR results revealed a higher grafting of octadecylamine (ODA) on the h-BNNPs compared to trioctylamine (TOA). The cohesive interaction between the alkyl chains grafted onto the h-BNNPs and the hydrocarbon chains of mineral lube base oil facilitates the dispersion of the alkylamine-functionalized h-BNNPs. The TOA-grafted h-BNNPs (h-BNNPs-TOA) exhibited long-term dispersion stability compared to the ODA-grafted h-BNNPs and this was attributed to a higher degree of van der Waals interactions between the octyl chains of the TOA molecules grafted onto the h-BNNPs and the hydrocarbon chains of the mineral lube base oil. The tribo-performance of the h-BNNPs-TOA as an additive to mineral lube base oil was evaluated in terms of the coefficient of friction and wear using ball-on-disc contact geometry. A minute dosing (0.02 mg mL(-1)) of h-BNNPs-TOA significantly improved the lubrication characteristics of the mineral lube base oil and showed a 35 and 25% reduction of friction and wear, respectively. The presence of boron and nitrogen on the worn scar of an aluminium disc, as deduced from elemental mapping, confirmed the formation of a tribo-chemical thin film of h-BN lamellae on the contact interfaces, which not only reduced the friction but also protected the contact interfaces against undesirable wear events.

IscS from Archaeoglobus fulgidus has no desulfurase activity but may provide a cysteine ligand for [Fe2S2] cluster assembly

Iron sulfur ([Fe–S]) clusters are essential prosthetic groups involved in fundamental cell processes such as gene expression regulation, electron transfer and Lewis acid base chemistry. Central components of their biogenesis are pyridoxal-5′-phosphate (PLP) dependent l-cysteine desulfurases, which provide the necessary S atoms for [Fe–S] cluster assembly. The archaeon Archaeoglobus fulgidus (Af) has two ORFs, which although annotated as l-cysteine desulfurases of the ISC type (IscS), lack the essential Lys residue (K199 in Af) that forms a Schiff base with PLP. We have previously determined the structure of an Af(IscU–D35A–IscS)2 complex heterologously expressed in Escherichia coli and found it to contain a [Fe2S2] cluster. In order to understand the origin of sulfide in that structure we have performed a series of functional tests using wild type and mutated forms of AfIscS. In addition, we have determined the crystal structure of an AfIscS–D199K mutant. From these studies we conclude that: i) AfIscS has no desulfurase activity; ii) in our in vitro [Fe2S2] cluster assembly experiments, sulfide ions are non-enzymatically generated by a mixture of iron, l-cysteine and PLP and iii) the physiological role of AfIscS may be to provide a cysteine ligand to the nascent cluster as observed in the [Fe2S2]–Af(IscU–D35A–IscS)2 complex. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases.

ChemInform Abstract: Quantum Mechanochemistry Understanding of Tribochemical Reactions

AbstractReview: 80 refs.