Lone Pair Research Articles

Strain-induced thermal switches with a high switching ratio in monolayer boron sulfide

Manipulating the thermal conductivity of materials and achieving a high thermal switching ratio is very important in fields such as thermal management and energy conversion. In this study, by utilizing first-principles calculations and semi-classical Boltzmann transport theory, we find the lattice thermal conductivity (κl) of monolayer boron sulfide (BS) can reach values as low as 0.11 Wm−1 K−1 at room temperature, significantly lower than that of well-known two-dimensional materials with low thermal conductivity such as SnSe. This phenomenon is mainly caused by the strong lattice anharmonicity, which is primarily induced by the lone electron pairs. The effect of biaxial strain on κl is further investigated. It is found that a small strain of 2% can lead to a two orders of magnitude increase in κl. Moreover, this property remains stable within the strain range of 2%–7%, making it easier to achieve experimentally. The variation of κl with strain is mainly determined by the change in phonon lifetime, which is governed by the competition between the reduction of anti-bonding valence band states and the enhanced coupling between soft optical and acoustic phonons. Our results indicate that monolayer BS is a promising candidate material for thermal switches and energy conversion devices.

Thermoelectric Properties of a Light Compound Fe2S2: the Role of Electron Correlation Strengthened Spin-Orbital Coupling.

Spin-orbit coupling (SOC) induced nontrivial bandgap and complex Fermi surface has been considered to be profitable for thermoelectrics, which, however, is generally appreciable only in heavy elements, thereby detrimental to practical application. In this study, the SOC-driven extraordinary thermoelectric performance in a light 2D material Fe₂S₂ is demonstrated via first-principles calculations. The abnormally strong SOC, induced by electron correlation through 3d orbitals polarization, significantly renormalizes the band structures, which opens the bandgap via Fe 3d orbitals inversion, exposes the second conduction valley with weak electron-phonon coupling, and aligns the energy of Fe 3d and S 3p orbitals with divergent momentum in valence band. Such topological band renormalization triggers improvement of both p- and n-type power factors by more than 200%. Combining with the low lattice thermal conductivity caused by lone pair electrons and intense high-order phonon scattering, the peak zT can reach 1.6 and 1.8 for p- and n-type Fe₂S₂ at 400 K, respectively. This work unravels the mechanism of SOC-provoked high zT in electron correlation systems, which inspires the development of high-performance thermoelectric materials without heavy and scarce elements.

Stereoactive Lone-Pair Manipulation for High Thermoelectric Performance of GeSe-Based Compounds.

Materials with high crystallographic symmetry are supposed to be good thermoelectrics because they have high valley degeneracy (NV) and superb carrier mobility (μ). Binary GeSe crystallizes in a low-symmetry orthorhombic structure accompanying the stereoactive 4s lone pairs of Ge. Herein, we rationally modify GeSe into a high-symmetry rhombohedral structure by alloying with GeTe based on the valence-shell electron-pair repulsion theory. We demonstrate that the substitution of Se by Te weakens the stereoactivity of the Ge lone-pair electrons, resulting in robust rhombohedral structures of GeSe1-xTex for x ≥ 0.3 at room temperature. The increase of crystal symmetry not only boosts NV from 2 for orthorhombic GeSe to 9 for rhombohedral GeSe1-xTex but greatly enhances μ from <5 to >10 cm2 V-1 s-1 (room-temperature values), thereby remarkably elevating the power factors by 2 orders of magnitude (26.9 μW cm-1 K-2 at 638 K for x = 0.5). Surprisingly, despite their higher crystallographic symmetry, rhombohedral GeSe1-xTex compounds display even lower lattice thermal conductivities (∼1.0 W m-1 K-1 at 300 K for x = 0.5) than binary GeSe (∼2.5 W m-1 K-1 at 300 K) due to abundant alloying defects in the Se-Te sublattice and ferroelectric instability. Altogether, a maximum ZT value of ∼1.1 at 638 K is achieved in rhombohedral GeSe0.5Te0.5, which already outperforms GeTe. This work provides an avenue for engineering the thermoelectric properties of low-symmetry compounds containing lone-pair electrons.

Exploring new horizons in mid-to-far infrared nonlinear optical crystals: the significant potential of trigonal pyramidal [TeS3]2- functional units.

Traditional tetrahedral-based mid-to-far infrared (MFIR) nonlinear optical (NLO) crystals often face limitations due to the optical anisotropy constraints imposed by their highly symmetric structures. In contrast, the relatively rare trigonal pyramidal [TeS3]2- functional unit characterized by its asymmetric structure and stereochemically active lone pair (SCALP), offers improved optical anisotropy, hyperpolarizability and a broader IR transparency range. Despite its potential, synthetic challenges have hindered the development of MFIR NLO crystals that incorporate this unit, with only one example reported to date. Herein, an innovative MFIR NLO crystal, Cu10Te4S13 has been successfully constructed using the trigonal pyramidal [TeS3]2- units, via a simple high-temperature solid-state method. The novel three-dimensional structure of Cu10Te4S13 is interconnected by butterfly-orchid-like [Cu6Te4S13] anionic clusters and [CuS4] groups, where the former are composed of trigonal pyramidal [TeS3]2- groups and [Cu6S13] hexamers. Cu10Te4S13 exhibits a remarkable second harmonic generation effect, approximately 3.75 times that of AgGaS2 at 2900 nm in the particle size range of 30-45 μm. Additionally, it demonstrates favorable crystal growth habits, producing single crystals with maximum dimensions of about 7 × 3 × 2 mm3. This polished single crystal appears to exhibit complete transparency within the MFIR spectral window ranging from 2.5 to 25 μm, representing the widest IR transmission in all reported NLO chalcogenides. Furthermore, the structure-property relationship is also elucidated through first-principles analysis. This work confirms the potential of the unique trigonal pyramidal [TeS3]2- as a MFIR NLO functional unit, paving the way for the development of unconventional MFIR NLO materials.

A HTO-Type Nonlinear Optical Fluorophosphate with Ultrawide Bandgap.

Compounds having hexagonal tungsten oxides (HTO) topology are of intense research interests owing to their potential functional properties, such as nonlinear optical (NLO) performances. However, most of the reported HTO-type compounds exhibit narrow optical bandgaps because of the d-d electronic transition of compositional d0 transition metals and lone pair electrons effect of Se4+/Te4+, which hinder their applications in the high-energy field, such as deep-ultraviolet (deep-UV) region. In this work, a new fluorophosphate, (NH4)3[Sc3F5(PO4)](PO3F)2 exhibiting HTO-topological structures is reported. Remarkably, the compound shows an ultrawide optical bandgap (Eg(exp.) >6.2eV, Eg(cal.) = 6.724eV), surpassing those of reported HTO-type compounds. The fact is mainly ascribed to the collaborative effect of Sc3+ without destructive d-d transition, the PO4 and PO3F units having large LUMO-HOMO gaps. Furthermore, it exhibits a phase-matchable second-harmonic generation (SHG) response of ca. 0.65 × KDP, underscoring its potential use for NLO applications. This work provides new opportunities for discovering HTO-type NLO crystals with ultrawide bandgaps.

Insight into the Origin of Second Harmonic Generation and Rational Design in the Metal Halide Borates.

Metal halide borates are promising candidates for high-performance nonlinear optical (NLO) applications, yet the origins of their second harmonic generation (SHG) properties remain unclear. Using atom response theory combined with density functional theory calculations, this study investigates why halogen substitution leads to distinctly different SHG responses in halide monoborates (Pb2BO3X) versus halide pentaborates (Pb2B5O9X). We find that the SHG origins vary between these two families due to differences in the strength of the Pb-X interactions. Interestingly, the stereochemically active lone pairs are not shown to be the primary contributors to SHG; instead, these hybridized asymmetric orbitals can introduce negative contributions. Utilizing the deffp vs αsum/(NEg) linear relationship, we predict 12 new NLO borates with strong SHG responses, including the promising NLO material Sn2B5O9I (19.2 × KDP), which is expected to exhibit the highest SHG response among halide borates reported to date. This work provides valuable insights into the relationship between elemental substitution and SHG modulation, guiding the design of advanced NLO materials.

Pnictogen Bond-Mediated Coassemblies for Noncovalent Molecular Glass.

Pnictogen bond (PnB) occurring on the group-15 elements is recognized as σ- or π-hole-based interaction that has garnered attention in the fields of anion recognition and organocatalysis. Due to the polyvalent feature of pnictogens and high directionality, PnB possesses potential in the design of convergent coassembled materials with acceptors containing lone pair electrons or anions, which however is rarely explored so far. Herein, we unveil the role of antimony (Sb)-based PnB donors in producing self-assembled chiroptical materials with lone pair electron containing acceptors. Steric effect and electronic properties determined the exposure and strength of σ-holes that direct the complexation between components. PnB complexation leads to profound property and self-assembly behavior evolutions compared to the pristine assembly, including crystallinity, photophysical, morphological, and chiroptical properties. The PnB complexes exhibited an accelerated photoisomerization. Ascribed to the multiple σ-holes in Sb donors, amorphous structures were generated, enabling the formation of glassy materials.

Binary solvent participation in crystals of a multi-aromatic 1,2,3-triazole.

The X-ray crystal structure of a multi-aromatic substituted 1,2,3-triazole is presented, which shows an extensive three-dimensional hydrogen-bonding network involving two water mol-ecules and two aceto-nitrile mol-ecules. The structure of 4-{[(4-{[1-({[(3,4-di-meth-oxy-phen-yl)meth-yl](3-acetamido-phen-yl)carbamo-yl}meth-yl)-1H-1,2,3-triazol-4-yl]meth-oxy}-3-meth-oxy-phen-yl)meth-yl]amino}-benzoic acid-aceto-nitrile-water (1/2/2), C37H38N6O8·2C2H3N·2H2O, features amine-linked aromatic groups that have a variety functionality including a carb-oxy-lic acid, an acetamido group, and meth-oxy ethers. All X-H groups, and seven out of ten heteroatoms with available lone-pair electrons, participate in hydrogen bonding, with the aid of dimer-bridging water mol-ecules and aceto-nitrile mol-ecules whose methyl groups form close contacts with oxygen atoms. The triazole itself is a dimer made using click chemistry from readily available and inexpensive starting materials and is a precursor to larger oligomers, as well as to compounds with a wide array of readily manipulated functionality.

Enhancing the tribopositive characteristics of polyvinyl alcohol (PVA)-carbon composites by optimizing the PVA-carbon interaction with various carbon fillers.

Incorporating carbon-based fillers into triboelectric nanogenerators, TENGs, is a compelling strategy to enhance the power output. However, the lack of systematic studies comparing various carbon fillers and their impact on tribopositive contact layers necessitates further research. To address these concerns, various carbon fillers (including buckminsterfullerene (C60), graphene oxide (GO), reduced graphene oxide (rGO), multi-wall carbon nanotube (MWCNT), and super activated carbon (SAC)) with distinct structural and electrical properties are mixed with polyvinyl alcohol, PVA, to form PVA-carbon composites and used as tribopositive layers in the contact-separation of TENGs. The results show that PVA-SAC provides the largest enhancements to the electrical outputs of the TENG. At the optimal loading of 1 wt%, PVA-SAC composites yielded a peak power density of 12.8 W m-2, a substantial 220% enhancement compared to pristine PVA. The mechanism governing the enhancement is determined by analysing the changes in electrical and structural characteristics caused by the addition of various carbon fillers. Dielectric measurements indicated that enhanced dielectric properties did not significantly contribute to the observed increase in the triboelectric performance. Instead, Raman and FTIR analyses revealed a correlation between the PVA-carbon interactions and an increase in the D/G ratio of carbon fillers, accompanied by a reduction in hydrogen-bonded -OH groups within PVA. This suggests that the interaction between the π electrons of sp2 hybridized carbon atoms and the oxygen lone pairs in PVA inhibits hydrogen bond formation, leading to an increase in free -OH groups. Consequently, these free -OH groups enhanced the electron-donating capability and improved the tribopositive behaviour of the PVA-carbon composites. Our results proved that filler-matrix interactions are paramount in engineering high-performance TENGs by controlling the electron affinity of the triboelectric layers.

Coordination complexes of PIII-doped heterobuckybowls and their applications in catalysis.

Doping the π-frameworks of polycyclic aromatic hydrocarbons (PAHs) with main-group elements is a powerful strategy to manipulate optoelectronic properties. Herein, the benzylic carbons of π-bowl sumanene are replaced with chalcogens (S, Se, and Te) and trivalent phosphorus (PIII), affording a series of PIII-doped heterosumanenes (HSEs). The lone-pair electrons of the PIII-dopant endow these HSEs with pronounced affinity toward transition metals (Au+, Pt2+, and Pd2+). Accordingly, nine coordination complexes were synthesized to exhibit diverse coordination patterns contingent upon the metal ions and chalcogen atoms on HSEs. For the first time, we proved that the Pd2+ complexes of these HSEs are promising catalysts for the Suzuki-Miyaura coupling reaction of aryl chlorides.

Characterization of 3-Chloro-4-Fluoronitrobenzene Molecule with New Calculation Methods and Discussions for Advanced Applied Sciences

This current research characterizes 2-chloro-1-fluoro-4-nitrobenzene molecule via the Hartree Fock (HF) and density functional theory (DFT) quantum mechanical computational techniques using B3LYP/6-311++G(d,p) levels of computation. The molecular geometries, thermodynamic quantities at 300 K, NMR chemical shifts, corresponding vibrational spectra, UV-vis spectra, vibrational frequencies, and atomic point charge distributions are extensively investigated. The 1H and 13C NMR chemical shifts, and theoretical vibrational frequencies are compared to the experimental results. It is obtained that all calculations are in agreement with the available experimental data which has the 1H isotropic chemical shifts range from 8.306 ppm to 7.235 ppm, while the computed values range from 9.0368 ppm to 6.8397 ppm, 8.3213 ppm to 6.1242 ppm at DFT and HF GIAO levels, respectively. Besides, calculated 13C chemical shifts vary from 141.83 ppm to 186.394 ppm and from 129.743 ppm to 174.373 ppm by using DFT and HF in CH4, while these values are in the range of 117.00 ppm to 164.59 ppm, experimentally. This points out that the chosen computation sets are highly effective methods for identifying and characterizing the compound. In addition, simulations are performed to examine frontier molecular orbitals, electrostatic potential, and molecular electrostatic potential regions. Key properties such as dipole moment, chemical hardness, transition states, electronegativity, molecular softness, nucleophilic aromatic regions, electrophilicity index, and energy band gap are also analyzed to explore potential future applications such as advanced applied sciences, industry, chemistry, medical, physics, biology, pharmaceuticals, dyes, and agrochemicals of the compound. Additionally, it is noted that the compound contains significant intramolecular charge transfer (ICT) regions, lone electron pairs, electron-donating groups, π-bond conjugation, and particularly reactive electrophilic and nucleophilic aromatic sites. Accordingly, it is pointed out that the molecule has a strong potential for metallic bonding as well as various intermolecular interactions. In summary, this study provides valuable information that will benefit both basic research and technological or industrial applications by increasing the understanding of physical, chemical, structural, and reactive features of the 3-chloro-4-fluoronitrobenzene molecule.

Reactivity of Anomalous Aziridines for Versatile Access to High Fsp3 Amine Chemical Space.

ConspectusThe manipulation of strained rings is a powerful strategy for accessing the valuable chemical frameworks present in natural products and active pharmaceutical ingredients. Aziridines, the smallest N-containing heterocycles, have long served as building blocks for constructing more complex amine-containing scaffolds. Traditionally, the reactivity of typical aziridines has been focused on ring-opening by nucleophiles or the formation of 1,3-dipoles. However, over the past decade, our group has pioneered highly chemo-, site-, and stereoselective Ag- and Rh-catalyzed nitrene transfer (NT) reactions of allenes and alkenes to furnish unusual, or "anomalous", aziridines. The unique features of these aziridines, coupled with our ability to control the fate of strained intermediates resulting from diverse reactions of these precursors, allow for their transformation to densely substituted, stereochemically complex N-heterocyclic structures that would otherwise be difficult to access using conventional strategies. Our research is driven by a keen interest in versatile synthetic approaches that explore high Fsp3 (the fraction of sp3 carbons relative to the total number of carbons in a molecule) amine chemical space, which holds promise for uncovering novel bioactivity toward challenging protein targets. We begin by outlining the design and synthesis of selected anomalous aziridines and highlighting the key features that are pertinent to their versatility as synthetic intermediates. We detail chemo-, site-, and stereoselective Rh-catalyzed NT of homoallenic sulfamates leading to the key (E)-methyleneaziridines (MAs) and the development of new Ag catalysts to achieve chemo- and enantioselective aziridinations of homoallenic and homoallylic carbamates/carbamimidates to yield bicyclic (methylene)aziridines. The chemoselective Ag-catalyzed NT of carbamimidates to accomplish intramolecular aza-Büchner reactions via polycyclic aziridine intermediates is also highlighted. Next, we focus on unlocking several modes of reactivity of our anomalous aziridines. These include regioselective ring-opening with nucleophiles and subsequent functionalization to afford amine stereotriads, the stereocontrolled formation and reaction of 2-amidoallyl cations, and alkene oxidation of endo- and exocyclic MAs. Additionally, due to the unusual molecular geometry of bicyclic (methylene)aziridines, the nitrogen lone pair can react with carbenes to generate aziridinium ylides that can be diverted along multiple pathways. From only a handful of anomalous aziridines, our chemistry is capable of delivering amine stereotriads, azetidines, azetidinones, piperidines, aminated cyclopentanes and cycloheptanes, azepines, and azepanes. Finally, we discuss our efforts to leverage this chemistry to explore the complex amine chemical space relevant to the natural products jogyamycin and methyl detoxinine. Ultimately, our goal is to use these methods to generate DNA-encoded libraries of high Fsp3 compounds with potential activity against difficult-to-target proteins.

Control of Crystallization Pathways in the BiFeO3-Bi2Fe4O9 System.

Bismuth ferrites, specifically perovskite-type BiFeO3 and mullite-type Bi2Fe4O9, hold significant technological promise as catalysts, photovoltaics, and room-temperature multiferroics. However, challenges arise due to their frequent cocrystallization, particularly in the nanoregime, hindering the production of phase-pure materials. This study unveils a controlled sol-gel crystallization approach, elucidating the phase formation complexities in the bismuth ferrite oxide system by coupling thermochemical analysis and total scattering with pair distribution function analysis. We tune the crystallization pathways in the BiFeO3-Bi2Fe4O9 system by adjusting the metal to complexing agent ratio and pH during precursor preparation with a fixed Bi/Fe ratio of 1:2. Although all precursors undergo an amorphization process during heating, our results demonstrate a consistent correlation between the crystallization pathway and the initial structural entities formed during gel formation. Pair distribution function analysis reveals structural differences in the intermediate amorphous structures, which preferentially crystallize into either BiFeO3 or Bi2Fe4O9. This study offers mechanistic insights into the formation processes in the system and synthetic guidance for the controlled synthesis of pure Bi2Fe4O9 and mixed BiFeO3/Bi2Fe4O9 nanomaterials. Additionally, it elucidates the unusual growth behavior and structural size dependence of Bi2Fe4O9, particularly highlighting significant distortions in the local structure likely induced by the proximity of Bi's stereoactive lone electron pairs at small sizes.

Suppressing Zinc Metal Corrosion by an Effective and Durable Corrosion Inhibitor for Stable Aqueous Zinc Batteries

AbstractThe development of aqueous zinc‐ion batteries (AZIBs) for large‐scale industrial applications is substantially constrained by the persistent issue of zinc anode corrosion. This study introduces fucoidan (FCD), a corrosion inhibitor, to effectively mitigate the corrosion‐related challenges in zinc metal anodes. FCD forms a robust, covalently bonded layer on the zinc surface at a low concentration of 25 mm through interactions between the lone pairs on its polar atoms and the d orbitals of zinc. This layer is ultrathin, which does not deteriorate ion transfer but effectively shields the zinc from corrosive electrolytes and promotes uniform zinc deposition, resulting in suppressed corrosion, passivation, and dendrite formation. Consequently, the Zn||Zn cells exhibit excellent reversibility, stably operating for 2700 h at 1 mA cm−2 under 1 mAh cm−2 and 400 h at 10 mA cm−2 under 10 mAh cm−2. Furthermore, a large‐sized Zn||I2 pouch cell with a high iodine loading of 2 g and a discharge capacity of ≈300 mAh is demonstrated, which shows minimal capacity degradation—&lt;3% after 300 cycles—and maintains a high Coulombic efficiency of ≈99.5%. The corrosion inhibition strategy proposed in this study provides crucial insights for enhancing the durability and practicability of AZIBs.

Exploring Intrinsic and Extrinsic p-Type Dopability of Atomically Thin β-TeO2 from First Principles.

Two-dimensional (2D) β-TeO2 has gained attention as a promising material for optoelectronic and power device applications, thanks to its transparency and high hole mobility. However, the mechanisms driving its p-type conductivity and dopability remain elusive. In this study, we investigate the intrinsic and extrinsic point defects in monolayer and bilayer β-TeO2, the latter of which has been experimentally synthesized, using the Heyd-Scuseria-Ernzerhof (HSE) + D3 hybrid functional. Our results reveal that most intrinsic defects are unlikely to contribute to p-type doping in 2D β-TeO2. Moreover, Si and H contamination could further impair p-type conductivity. Since the point defects do not contribute to p-type conductivity, we suggest two possible mechanisms for hole conduction: hopping conduction via localized impurity states, and substrate effects. We also explored substitutional p-type doping in 2D β-TeO2 with 10 trivalent elements. Among these, the Bi dopant is found to exhibit a relatively shallow acceptor transition level. However, all the dopants introduce deep localized states, where hole polarons are trapped by the lone pairs of Te atoms. Interestingly, monolayer β-TeO2 shows potential advantages over bilayers due to reduced self-compensation effects for p-type dopants. These findings provide valuable insights into defect engineering strategies for future electronic applications involving 2D β-TeO2.

Triazolide Complexes of Sodium and Potassium in the Gas Phase.

Aromatic organometallic complexes, such as ferrocene and the "inverse sandwich complex" [Na2Cp]+, are stabilized via charge-transfer (C-T) interactions and cation-π interactions (i.e., charge-induced dipole and charge-quadrupole interactions). Much effort has gone into investigating systems that contain organic moieties, such as benzene or cyclopentadienyl ligands, but less attention has been paid to aromatic systems that contain heteroatoms (e.g., N), possibly owing to the complexity arising from a lowering of symmetry and the introduction of electron lone pair density and dipole moments. Here we investigate sodiated and potassiated clusters of 1,2,3-triazolide, [Mx (123T)x-1]+ (x = 3, 4; M = Na, K), and 1,2,4-triazolide, [Mx (124T)x-1]+ (x = 3, 4; M = Na, K), using a combination of infrared ion spectroscopy (IRIS) and DFT calculations. Cluster structures are strongly influenced by charge-dipole interactions and C-T interactions from N lone pairs to the metal cations. IRIS spectra indicated that the geometries of the triazolide moieties are essentially unperturbed by the interaction with the metal ions. Additional spectral features, not predicted by DFT calculations, that are observed in the 1500-1800 cm-1 region seem to be associated with combination bands involving C-H wagging and ring torsion motions.

Reversible Metal-Mediated Molecular Switching of a Phosphaethene Polyaromatic Hydrocarbon.

This experimental and theoretical study illustrates how phosphaalkenes, which are isolobal to alkenes, can utilize a variety of external triggers for molecular switching. The E/Z isomerization of a truxene-based phosphaalkene, i. e. TruxC=P-Mes* (Mes*=2,4,6-tris-t-butyl-benzene), is accomplished by irradiation, metal coordination, or deprotonation of the truxene core. The reversible and quantitative Z/E double bond isomerization by gold(I) coordination/decoordination of the phosphorous lone pair represents a novel fuelling strategy for molecular switches.

Deprotonation of diphenylsilane with organosilyllithium agents

Although there are many reports on deprotonation of carbon analogues, there are only a few reports on deprotonation from silanes. This is because the lone pair of a base mainly attacks hydrogen of a C–H bond and deprotonates, whereas in the case of silanes, the base is added to the silicon atom of a Si–H bond. Previous reports have shown that deprotonation from silanes requires the assistance of negative hyperconjugation by silyl substituents or intramolecular chelating groups (pincer ligands). We proposed that lithium and hydrogen exchange approach could be applied to the deprotonation of monosilanes using bulky silyllithium instead of some bulky strong bases, such as t-butyllithium and LDA. Here, we report the first successful approach to the deprotonation of monosilanes without intramolecular chelation.

Pseudo‐silapnictene and Bis(pseudo‐silapnictene) – Hyperconjugatively Stabilized Heavier Analogues of Imine and Ethane‐1,2‐diimine

The equilibrium geometry, bonding, and proton affinity of the pseudo‐silapnictenes and the bis(pseudo‐silapnictenes) are explored using computational quantum mechanical calculations carried out at M06/def2‐TZVPP//BP86‐D3(BJ)/def2‐SVP level of theory. The pseudo‐silapnictene 1E features a dicoordinated, monovalent group‐15 center having two lone pairs of σ‐ and π‐local symmetry. Both the lone pairs are stabilized by hyperconjugative donation to the silylene fragment. The extent of hyperconjugative stabilization of π‐type lone pair is higher than that of σ‐type lone pair and is comparable to classical Si‐E π‐bonds. Accordingly, the former interactions can be considered as pseudo‐π‐bonding interactions. The strength of the pseudo‐π‐bond reduces as the group‐15 element changes from nitrogen to bismuth. Hence, 1E can be considered as heavier analogues of imine. Even though these lone pairs are stabilized by hyperconjugative interactions, they are very reactive as indicated by the very high values of first and second proton affinities. In the bis(pseudo‐silapnictene) 2E, two Si‐E pseudo‐π‐bonds formed by hyperconjugative interactions are delocalized over the E‐Si‐Si‐E skeleton. Since the π‐bonds are majorly localized on the group‐15 element, the extent of delocalization is quite less than that of the classical π‐delocalized system. Nevertheless, the bis(pseudo‐silapnictene) can be considered as the heavier analogue of ethane‐1,2‐diimine.

Program-Modulated Kinetics of Perovskite-Film Growth by Molecular "Thruster" for High-Efficiency and Stable Perovskite Solar Cells.

The rapid reaction between lead iodide (PbI2) and formamidinium iodide (FAI) complicates the fabrication of high-quality formamidinium lead iodide (FAPbI3) films. Conventional methods, such as using nonvolatile small molecular additives to slow the reaction, often result in buried interfacial voids and molecule diffusion, compromising the devices' operational stability. In this study, we introduced a molecular "thruster"-a hypervalent iodine (III) compound with three carbonyl groups and a C--I+ bond-that possesses coordination and dissociation abilities, enabling programed modulation of perovskite-film growth kinetics. Initially, the three carbonyl groups coordinate with PbI2 to slow the reaction between FAI and PbI2, preventing δ-phase formation. As temperature rises, the C--I+ bond dissociates, promoting perovskite growth and the dissociated product iodobenzene will promote solvent volatilization, thus avoiding buried interfacial voids. Another product, a carbene compound with eight lone pair electrons sufficiently passivate the undercoordinated Pb2+ defects and anchors at grain boundaries without diffusion. Consequently, the resultant FAPbI3 film displays high-quality with enhanced phase purity, compact morphology, and reduced defects. Evidently, 0.062- and 1.004-cm2 pero-SCs achieve power conversion efficiencies (PCEs) of up to 26.06 % (25.79 % certified) and 24.65 %, respectively. This approach also controls perovskite-film growth on plastic substrates, resulting in flexible pero-SCs with an impressive PCE of 25.12 %.