Intramolecular Charge Distribution Research Articles

Influence of Donor Skeleton on Intramolecular Electron Transfer Amount for Efficient Perovskite Solar Cells

The passivation of the defects derived from rapid‐crystallization with electron‐donating molecules is always a prerequisite to obtain desirable perovskite films for efficient and stable solar cells, thus, the in‐depth understanding on the correlations between molecular structure and passivation capacity is of great importance for screening passivators. Here, we introduce the double‐ended amide molecule into perovskite precursor solution to modulate crystallization process and passivate defects. By regulating the intermediate bridging skeletons with alkyl, alkenyl and benzene groups, the results show the passivation strength highly depends on the spin‐state electronic structure that serves as an intrinsic descriptor to determine the intramolecular charge distribution by controlling orbital electron transfer from the donor segment to acceptor segment. Upon careful optimization, the benzene‐bridged amide molecule demonstrates superior efficacy on improving perovskite film quality. As a physical proof‐of‐concept, the carbon‐based, all‐inorganic CsPbI2Br solar cell delivers a significantly increased efficiency of 15.51% with a remarkably improved stability. Based on the same principle, a champion efficiency of 24.20% is further obtained on the inverted (Cs0.05MA0.05FA0.9)Pb(I0.93Br0.07)3 solar cell. These findings provide new fundamental insights into the influence of spin‐state modulation on effective perovskite solar cells.

Influence of Donor Skeleton on Intramolecular Electron Transfer Amount for Efficient Perovskite Solar Cells.

The passivation of the defects derived from rapid-crystallization with electron-donating molecules is always a prerequisite to obtain desirable perovskite films for efficient and stable solar cells, thus, the in-depth understanding on the correlations between molecular structure and passivation capacity is of great importance for screening passivators. Here, we introduce the double-ended amide molecule into perovskite precursor solution to modulate crystallization process and passivate defects. By regulating the intermediate bridging skeletons with alkyl, alkenyl and benzene groups, the results show the passivation strength highly depends on the spin-state electronic structure that serves as an intrinsic descriptor to determine the intramolecular charge distribution by controlling orbital electron transfer from the donor segment to acceptor segment. Upon careful optimization, the benzene-bridged amide molecule demonstrates superior efficacy on improving perovskite film quality. As a physical proof-of-concept, the carbon-based, all-inorganic CsPbI2Br solar cell delivers a significantly increased efficiency of 15.51 % with a remarkably improved stability. Based on the same principle, a champion efficiency of 24.20 % is further obtained on the inverted (Cs0.05MA0.05FA0.9)Pb(I0.93Br0.07)3 solar cell. These findings provide new fundamental insights into the influence of spin-state modulation on effective perovskite solar cells.

Efficient cavity-enhanced adsorption and recovery of low-concentration ammonia on pillar[5]arenes

Ammonia (NH3) capture has great implications for environmental protection and resource recovery. Developing effective and recyclable adsorbent materials to remove low-concentration NH3 in industrial waste gas is critical. Here, solid adsorbents per-hydroxylated pillar[5]arene (OHP[5]) and pillar[5]quinone (P[5]Q) with well-designed functional groups were synthesized and evaluated for NH3 adsorption. The results showed that both materials have high NH3 uptake capacity and excellent cycle stability. P[5]Q showed higher NH3 capacity (15.4 mmol/g) than OHP[5] (11.5 mmol/g) at ambient conditions (293.2 K and 1.0 bar). Dynamic breakthrough experiments showed that P[5]Q had good separation performance on low concentration NH3. Characterizations (including FTIR, SEM, and XPS) and density functional theory (DFT) studies revealed that the adsorption strength for NH3 on P[5]Q possessing CO groups was stronger than OHP[5] composed of phenolic hydroxyls. Also, the electron-accepting CO groups on P[5]Q could change the intramolecular charge distribution, in which an amount of NH3 enters and stores in the electron-deficient internal cavity of P[5]Q. It is demonstrated that P[5]Q with the suitable cavity has good potential for separating low concentration NH3 from industrial waste gas.

A solid acid-catalyzed depolymerization of pine lignin to obtain guaiacol using a hydrogen-free strategy

Guaiacol is an important raw material to produce many value-added chemicals. Here, we report a strategy for directly cleaving the Car-Cα and Cβ-O bonds in pine lignin over a solid acid to generate guaiacol. The guaiacol yield in 90% methanol aqueous solution is up to 18.2 wt%, which is 5.6 wt% higher than that in methanol. The reaction pathway is proposed by combining controlled experiments with density functional theory. Different from previous views, the Car-Cα bond cleavage was found to be related to deacetylation, while the formation of Cα=O bond was found to change the intramolecular charge distribution and promote the Car-Cα bond cleavage through validation experiments. Adding water promotes methanol decomposition to produce more active hydrogen species and thereby promote the Car-Cα bond cleavage. This work provided a feasible pathway for obtaining guaiacol by directly cleaving the Car-Cα and Cβ-O bonds in lignin.

A comparative investigation for identification of N-(4-dimethylamino 3,5-dinitrophenyl)maleimide

This study has identified the characteristic behaviors of N-(4-dimethylamino 3,5-dinitrophenyl)maleimide molecule using ab initio Hartree-Fock (HF) and density functional theory (DFT) based on Becke’s three-parameter hybrid exchange functional combined with Lee-Yang-Parr non-local correlation function (HF/B3LYP and DFT/B3LYP) at 6-311G++(d,p) level of theory for the first time. On this basis, the optimized molecular structures, some thermodynamic features at 300 K, function groups of structures, charge distributions-dipole moments, molecular charge transfer regions, spectroscopic characteristic properties, vibrational frequencies, nuclear magnetic resonance chemical shifts of 13C-NMR and 1H-NMR spectra, and corresponding vibrational assignments have been investigated in detail. Comparisons between some experimental findings and theoretical results are performed to test the reliability of the calculation method preferred in the study. The comparison results in high correlation parameters such as R2 =0.976 and R2 =0.985 for the molecular structures and vibrational frequencies in the DFT and HF calculation levels, respectively. Moreover, the obtained vibrational frequencies and calculated results are in good agreement with the experimental data. Additionally, the simulations of highest/lowest occupied/unoccupied molecular orbital (HOMO and LUMO), molecular electrostatic potential (MEP), and electrostatic potential (ESP) maps have shown that there appear strong non-uniform intra-molecular charge distributions (ICT), electron engagements, lone pairs of electrons, π-π* conjugative effects based on the bond weakening, and intermolecular hydrogen bonding in the compound. Correspondingly, the molecule with the electrophilic reactive and nucleophilic regions has been noted to exhibit kinetical chemical stability. All the discussions have been confirmed by means of the findings of optimized molecular structures and vibrational frequencies belonging to the molecule.

Electronic, intermolecular, quantum computational investigations, molecular docking and simulation studies of the potent antiviral drug EIDD-2801

In this work, an analysis has been done to describe the molecular structure, spectroscopic, reduced density gradient, topological properties, atomic charges, Lipinski rule, Natural bond orbital analysis, docking and molecular dynamics simulation of the potent antiviral drug EIDD-2801 in the effective treatment against COVID-19. Intramolecular charge distribution is well understood by three schemes such as AIM, Mulliken and NBO analysis and non-covalent interactions have been understood through reduced density gradient. Topological properties, such as charge density and Laplacian of charge density along with the electron localization function, make it easy to obtain comprehensive information about bond strengths and critical points. The details obtained from the calculation of global reactivity descriptors and Lipinski rule are useful for understanding the nature of molecular reactivity and site selectivity. Electrostatic potentials help to identify potential electrophilic and nucleophilic sites for interaction between EIDD-2801 and target proteins. The molecular docking combined with molecular dynamic simulation studies enables us to get better picture about the ligand-protein interaction.

Sodium Ions Affect Pyrraline Formation in the Maillard Reaction With Lys-Containing Dipeptides and Tripeptides.

Advanced glycation end products (AGEs) are potentially-hazardous chemical compounds, produced by the Maillard reaction between reducing sugars and Lysine side-chain amino groups in proteins. AGEs are strongly associated with diabetes, Alzheimer's disease and atherosclerosis. Pyrraline, a sugar derivative of Lysine, is a major AGE and an established marker for the presence of dietary AGEs. In this study, the effects of NaCl and different dipeptide and tripeptide structures were compared on the formation of pyrraline-containing peptides and the glucose derivative 3-deoxyglucosone in the presence of glucose and at different NaCl concentrations. The physicochemical properties (polarizability, dipole moment, molecular volume and dissociation constant) and the thermodynamic properties of the peptides were determined. The amount of the pyrraline decreased significantly in the following order of peptides (at the same concentrations): Lys-Phe > Lys-Ala > Lys-Gly; Lys-Gly-Phe > Lys-Gly-Ala > Lys-Gly-Gly. The highest levels of both pyrraline and 3-deoxyglucosone occurred at 0.2 mol/L Na+. Sodium ions appear to alter the intramolecular electron density and charge distribution of the peptides and facilitate the reaction by stabilizing some of the intermediates in the reaction sequence.

Reactive Molecular Dynamics Investigation of Toluene Oxidation under Electrostatic Fields: Effect of the Modeling of Local Charge Distribution.

A reactive Molecular Dynamics (MD) study of toluene oxidation at high temperatures under externally applied electrostatic fields has been performed. The impact of the modeling of local charge distribution has been investigated by comparing the widely used Charge Equilibration (QEq) method with the Charge Transfer with Polarization Current Equalization (QTPIE) method, which shields charge transfers up to atomic orbitals and introduces molecular polarization. Using the latter method, it is possible to improve the computation of the atomic charges, which are a critical aspect for the numerical study of electric fields, and to capture important effects of the electric field on rotational and vibrational energies of the toluene molecule. Results show that a more comprehensive treatment of inter- and intramolecular charge distribution achieved through the QTPIE method leads to substantially different applied forces and oxidation rates of toluene compared to the QEq method. Using the QTPIE method, no significant effects of the electrostatic field on the toluene oxidation rate were observed for the range of temperatures and pressures studied here, which is in disagreement with the results obtained with the QEq method where a clear impact of the electrostatic field on the average oxidation rate was found. Therefore, when studying electric field effects with MD simulations, the choice of the method used for the charge equilibration is a key modeling assumption whose impact should be carefully evaluated.

Hydration Structure and Dynamics of the Favipiravir Antiviral Drug: A Molecular Modelling Approach

Abstract The hydration structure of the Favipiravir antiviral drug, at infinite dilution in water, was investigated by employing a systematic molecular modelling approach. An effective interaction potential model was employed for Favipiravir, using the intramolecular geometry and charge distribution from quantum chemical calculations performed in the present treatment and adopting well-established Lennard-Jones parameters. The hydration structure and related dynamics were further investigated by means of classical molecular dynamics simulations. These calculations have revealed the existence of different types of hydrogen bonds between Favipiravir and the surrounding water molecules, with continuous lifetimes in the sub picosecond range and intermittent lifetimes in the range of 0.8–5.4 ps. The self-diffusion coefficient of Favipiravir at 298.15 K was found to be three times lower than the value obtained for water in solution, while comparable to the values measured for other common painkillers, anti-inflammatory drugs, antibiotics and corticosteroids for asthma treatment. It was also revealed that the rotational motions of Favipiravir are more retarded in comparison with water and this is reflected in the calculated reorientational correlation times of specific intramolecular vectors. The results obtained could be useful for further pharmacokinetic and computer-aided docking studies to evaluate the efficiency of this antiviral drug.

Adsorption of Water Insoluble Porphyrin to Trioctahedral Layered Aluminosilicate and Its Surface Acidity

Abstract This study investigated the adsorption of a non-ionic water-insoluble organic molecule (meso-tetraphenylporphyrin, TPP) on a trioctahedral layered aluminosilicate (saponite, SP) in organic solvents in order to investigate properties of SP as an adsorbent for a wider variety of molecules, other than cationic or polar ones. The affinity of solvents for the layered aluminosilicate surface was an important factor for predicting the molecule’s adsorption proprieties. Namely, solvents with low affinity for the aluminosilicate should be selected so that molecules can approach the surface, thus prompting adsorption of the molecules. Under these conditions, TPP was adsorbed to SP due to their basicity and acidity. The acid on SP adsorbing TPP was revealed to be Lewis acid. The weaker acid strength (H0, estimated to be 0.8–1.5) compared with that of Brønsted acids appeared to be more suitable for adsorbents because molecules are recovered efficiently from SP where their intramolecular charge distributions are shifted. The acidity of SP is discussed quantitatively in this study because this has not been done thoroughly in comparison with dioctahedral aluminosilicates such as montmorillonite, which are conventionally used as catalysts.

The Influence of Distant Boundaries on the Solvation of Charged Particles

The long-ranged nature of the Coulomb potential requires a proper accounting for the influence of even distant electrostatic boundaries in the determination of the solvation free energy of a charged solute. We introduce an exact rewriting of the free energy change upon charging a solute that explicitly isolates the contribution from these boundaries and quantifies the impact of the different boundaries on the free energy. We demonstrate the importance and advantages of appropriately referencing the electrostatic potential to that of the vacuum through the study of several simple model charge distributions, for which we can isolate an analytic contribution from the boundaries that can be readily evaluated in computer simulations of molecular systems. Finally, we highlight that the constant potential of the bulk dielectric phase - the Bethe potential - cannot contribute to the solvation thermodynamics of a single charged solute when the charge distributions of the solvent and solute do not overlap in relevant configurations. But when the charge distribution of a single solute can overlap with the intramolecular charge distribution of solvent molecules, as is the case in electron holography, for example, the Bethe potential is needed when comparing to experiment. Our work may also provide insight into the validity of "extra thermodynamic assumptions" traditionally made during the experimental determination of single ion solvation free energies.

Organic Semiconducting Alloys with Tunable Energy Levels.

Continuous band structure tuning, e.g., doping with different atoms, is one of the most important features of inorganic semiconductors. However, this can hardly be realized in organic semicondutors. Here, we report the first example of fine-tuning organic semiconductor band structures by alloying structurally similar derivatives into one single phase. By incorporating halogen atoms on different positions of the backbone, BDOPV derivatives with complementary intramolecular or intermolecular charge distributions were obtained. To maximize the Coloumbic attractive interactions and minimize repulsive interactions, they form antiparallel cofacial stacking in monocomponent or in alloy single crystals, resulting in efficient π orbital overlap. Benefiting from self-assembly induced solid state "olefin metathesis" reaction, it was observed, for the first time, that three BDOPV derivatives cocrystallized in one single crystal. Molecules with different energy levels serve like the dopants in inorganic semiconductors. Consequently, as the total number of halogen atoms increased, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the alloy single crystals decreased monotonously in the range from -5.94 to -6.96 eV and -4.19 to -4.48 eV, respectively.

Surface Enrichment in Equimolar Mixtures of Non-Functionalized and Functionalized Imidazolium-Based Ionic Liquids.

For equimolar mixtures of ionic liquids with imidazolium‐based cations of very different electronic structure, we observe very pronounced surface enrichment effects by angle‐resolved X‐ray photoelectron spectroscopy (XPS). For a mixture with the same anion, that is, 1‐methyl‐3‐octylimidazolium hexafluorophosphate+1,3‐di(methoxy)imidazolium hexafluorophosphate ([C8C1Im][PF6]+[(MeO)2Im][PF6]), we find a strong enrichment of the octyl chain‐containing [C8C1Im]+ cation and a corresponding depletion of the [(MeO)2Im]+ cation in the topmost layer. For a mixture with different cations and anions, that is, [C8C1Im][Tf2N]+[(MeO)2Im][PF6], we find both surface enrichment of the [C8C1Im]+ cation and the [Tf2N]− (bis[(trifluoromethyl)sulfonyl]imide) anion, while [(MeO)2Im]+ and [PF6]− are depleted from the surface. We propose that the observed behavior in these mixtures is due to a lowering of the surface tension by the enriched components. Interestingly, we observe pronounced differences in the chemical shifts of the imidazolium ring signals of the [(MeO)2Im]+ cations as compared to the non‐functionalized cations. Calculations of the electronic structure and the intramolecular partial charge distribution of the cations contribute to interpreting these shifts for the two different cations.

Tip-Enhanced Raman Spectromicroscopy of Co(II)-Tetraphenylporphyrin on Au(111): Toward the Chemists' Microscope.

Atomically terminated and nanoscopically smooth silver tips effectively focus light on the angstrom scale, allowing tip-enhanced Raman spectromicroscopy (TER-sm) with single molecule sensitivity and submolecular spatial resolution. Through measurements carried out on cobalt-tetraphenylporphyrin (CoTPP) adsorbed on Au(111), we highlight peculiarities of vibrational spectromicroscopy with light confined on the angstrom scale. Field-gradient-driven spectra, orientational fingerprinting, and sculpting of local fields by atomic morphology of the junction are elucidated through measurements that range from 2D arrays at room temperature to single molecule manipulations at 5 K. Notably, vibrational Stark tuning within molecules, reflecting intramolecular charge distributions, becomes accessible when light is more localized than the interrogated normal modes. The Stark images of CoTPP reveal that it is saddled, and the distortion is accompanied by charge transfer to gold through the two anchoring pyrroles.

Impact of position of electron withdrawing cyano groups on nonlinear optical properties of centrosymmetric donor‐π‐acceptor system

AbstractTwo symmetrically substituted phenylenevinylene D‐A‐D′‐A‐D type siblings, (2Z,2′Z)‐2,2′‐(2,5‐dimethoxy‐1,4‐phenylene)bis(3‐(4‐(dimethylamino)phenyl)acrylonitrile) (↑‐dscn) and (2Z,2′Z)‐3,3′‐(2,5‐dimethoxy‐1,4‐phenylene)bis(2‐(4‐(dimethylamino)phenyl)acrylonitrile) (↓‐dscn), are prepared. We investigate the effect of different but symmetrical location of these cyano groups in vinylene bridges on the 1‐photon and 2‐photon absorption behaviors. We report that the closeness of CN group on the vinyl group to the central phenyl ring in ↑‐dscn induces an intramolecular geometric distortion between the central phenyl ring and vinylene group, preventing the effective π‐conjugation length in ground and excited states. Thus, the transition energy that is observed in 1‐photon absorption and fluorescence is larger in ↑‐dscn than in ↓‐dscn. This leads to a different intramolecular charge distribution, as a result of which the linear and nonlinear optical properties strongly depend on the position of acceptors. These results are theoretically unraveled in terms of charge transfer pathways, charge distribution, and charge distribution differences on transition.

Molecular Dynamics Simulations Illuminate the Role of Counterion Condensation in the Electrophoretic Transport of Homogalacturonans.

Homogalacturonans (HGs) are polysaccharide copolymers of galacturonic acid and its methylesterified counterpart. The inter- and intramolecular distributions of the methylesterifed residues are vital behavior-determining characteristics of a sample's structure, and much experimental effort has been directed to their measurement. While many techniques are able to measure the sample-averaged degree of methylesterification (DM), the measurement of inter- and intramolecular charge distributions are challenging. Here, molecular dynamics (MD) simulations are used to calculate the electrophoretic mobilities of HGs that have different amounts and distributions of charges placed along the backbone. The simulations are shown to capture experimental results well, even for low-DM samples that possess high charge densities. In addition, they illuminate the role that local counterion condensation can play in the determination of the electrophoretic mobility of heterogeneous blocky polyelectrolytes that cannot be adequately described by a single chain-averaged charge spacing.

Electrotunable Friction with Ionic Liquid Lubricants: How Important Is the Molecular Structure of the Ions?

Using nonequilibrium molecular dynamics simulations and a coarse-grained model of ionic liquids, we have investigated the impact that the shape and the intramolecular charge distribution of the ions have on the electrotunable friction with ionic liquid nanoscale films. We show that the electric field induces significant structural changes in the film, leading to dramatic modifications of the friction force. Comparison of the present work with previous studies using different models of ionic liquids indicate that the phenomenology presented here applies to a wide range of ionic liquids. In particular, the electric-field-induced shift of the slippage plane from the solid-liquid interface to the interior of the film and the nonmonotonic variation of the friction force are common features of ionic lubricants under strong confinement. We also demonstrate that the molecular structure of the ions plays an important role in determining the electrostriction and electroswelling of the confined film, hence showing the importance of ion-specific effects in electrotunable friction.

Imaging three-dimensional surface objects with submolecular resolution by atomic force microscopy.

Submolecular imaging by atomic force microscopy (AFM) has recently been established as a stunning technique to reveal the chemical structure of unknown molecules, to characterize intramolecular charge distributions and bond ordering, as well as to study chemical transformations and intermolecular interactions. So far, most of these feats were achieved on planar molecular systems because high-resolution imaging of three-dimensional (3D) surface structures with AFM remains challenging. Here we present a method for high-resolution imaging of nonplanar molecules and 3D surface systems using AFM with silicon cantilevers as force sensors. We demonstrate this method by resolving the step-edges of the (101) anatase surface at the atomic scale by simultaneously visualizing the structure of a pentacene molecule together with the atomic positions of the substrate and by resolving the contour and probe-surface force field on a C60 molecule with intramolecular resolution. The method reported here holds substantial promise for the study of 3D surface systems such as nanotubes, clusters, nanoparticles, polymers, and biomolecules using AFM with high resolution.

Restriction of Molecular Rotation and Intramolecular Charge Distribution in the Photoexcited State of Coumarin Dyes on Gold Nanoparticle Surface

Effect of molecular structure on the excited state dynamics, molecular rotation, and intramolecular charge distribution in the excited states of two structurally similar coumarin dyes, namely, coumarin 343 (C-343) and 7-diethyl amino coumarin 3-carboxylic acid (D-1421), on the Au nanoparticle (NP) surface has been investigated using steady state and time-resolved emission spectroscopy. In the first excited state (S1), both the coumarin dyes exist as a locally excited (LE) state in nonpolar solvent; however, in polar solvent, C-343 exists as intramolecular charge transfer (ICT) state and D-1421 predominantly exists as a twisted intramolecular charge transfer (TICT) state. Photoexcited C-343 molecules transfer energy to Au NP in aqueous solution; however, photoexcited D-1421 molecules do not transfer energy to Au NP due to poor overlap between emission band of D-1421 and plasmon absorption band of Au NP. Interestingly, emission intensity of the S1 state of D-1421 drastically increases on the Au NP surface d...

Structure and binding efficiency relations of QB site inhibitors of photosynthetic reaction centres.

Many herbicides employed in agriculture and also some antibiotics bind to a specific site of the reaction centre protein (RC) blocking the photosynthetic electron transport. Crystal structures showed that all these compounds bind at the secondary ubiquinone (QB) site albeit to slightly different places. Different herbicide molecules have different binding affinities (evaluated as inhibition constants, KI, and binding enthalpy values, ΔHbind). The action of inhibitors depends on the following parameters: (i) herbicide molecular structure; (ii) interactions between herbicide and quinone binding site; (iii) protein environment. In our investigations KI and ΔHbind were determined for several inhibitors. Bound herbicide structures were optimized and their intramolecular charge distributions were calculated. Experimental and calculated data were compared to those available from databank crystal structures. We can state that the herbicide inhibition efficiency depends on steric and electronic, i.e. geometry of binding with the protein and molecular charge distribution, respectively. Apolar bulky groups on N-7 atom of the inhibitor molecule (like t-buthyl in terbutryn) are preferable for establishing stronger interactions with QB site, while such substituents are not recommended on N-8. The N-4,7,8 nitrogen atoms maintain a larger electron density so that more effective H-bonds are formed between the inhibitor and the surrounding amino acids of the protein.