NPA Charges Research Articles

CH4 Carbonylation to Acetic Acid Using H2O as an Oxidant on a Rh-Functionalized UiO-67 Combined with Oriented External Electric Fields: Selectivity and Mechanistic Insights from DFT Calculations.

Acetic acid (CH3COOH), as an industrially important petrochemical product, is predominantly produced via multistep energy-intensive processes. The development of a rhodium single-site heterogeneous catalyst has received considerable attention due to its potential to transform CH4 into CH3COOH in a single step. Herein, the reaction mechanism for the generation of CH3COOH from CH4, CO, and H2O catalyzed by Rh-functionalized metal-organic framework (MOF) UiO-67 and the selectivity of products CH3COOH, formic acid (HCOOH), methanol (CH3OH), and acetaldehyde (CH3CHO) under the oriented external electric fields (OEEFs) were systematically explored by density functional theory (DFT) calculations. The results reveal that the insertion of CO into Rh-CH3 is the rate-determining step with a free energy barrier of 21.0 kcal/mol in CH4 carbonylation to CH3COOH. Upon applying an OEEF of Fx = +0.0050 au along the C-C bond, the rate-determining step shifts toward H2O decomposition with the barrier of 19.6 kcal/mol, significantly improving the selectivity for CH3COOH production, compared to the major competitive HCOOH route. The Brønsted-Evans-Polanyi (BEP) relationships between key transition states, field strength, and NPA charge transfer were established. This study may guide the rational design of atomically dispersed MOF catalysts for the selective coconversion of CH4 and CO to CH3COOH using H2O as the oxidant under the OEEF.

Why Are Some Pnictogen(III) Pincer Complexes Planar and Others Pyramidal?

Geometrically-constrained pnictogen pincer complexes have emerged in recent years as platforms for unique stoichiometric and catalytic chemical transformations. These complexes feature dynamic conformations ranging from fully planar at the pnictogen centre to distorted-pyramidal geometries, as well as variation between phases. Although the valued reactivity of pnictogen pincer complexes is ascribed to their geometries, there is no unified model to explain the observed conformational outcomes across different ligands and pnictogen centres. Here we propose such a model through computational analysis of more than 1300 structures across 64 complexes (16 ligands and 4 heavy pnictogens), explaining the experimental observations and making new predictions. By looking at signatures of bond stability (bond lengths, Wiberg bond indices) and delocalization (NPA charges, Hirshfeld charges), our framework posits a pnictogen-based σ-bonding effect that favours pyramidalization and exists in competition with a ligand-based π-bonding effect that favours planarity. Variations in structure as a function of pnictogen identity, ligand tethering, electronics, and aromaticity can be reconciled with reference to a balance between these two opposing forces. Careful consideration of the σ/π-bonding effects may aid in the rational design of future pnictogen pincer complexes with predictable geometries and reactivities.

Engineering novel alkalides with superalkali clusters: Ab initio insights into nonlinear optical responses

ABSTRACT We designed novel alkalides such as FLi2-M-OLi3 and FLi2-M-NLi4 (M = Li, Na, K), along with OLi3-M-NLi4 (M = Li, Na) by interacting alkali metal atoms with heterogeneous superalkali clusters in anionic, neutral and cationic configurations. The stability of these superalkali based alkalides are confirmed by its binding energy (Eb ). Utilising QTAIM method, the bond strength and nature of bond have been analysed. NPA charge analysis is conducted to forecast charge transfer and also to confirm the alkalide character of the complex along with the electron localisation function (ELF) analysis. The HOMO–LUMO gap analysis is performed to analyse electrical conductivity and chemical reactivity. The nonlinear optical (NLO) properties have been investigated by polarisability and first-order static hyperpolarizibilty (β0 ), which is found to be as high as 2.77 × 107 a. u. for (OLi3-Li-NLi4)+ complex. The UV-Vis spectra and electronic transitions are used to explain the enhanced NLO responses. The study not only identifies new alkalide candidates but also presents strategies to significantly improve their NLO properties, which may be useful in nonlinear optics and optoelectronics.

Thermodynamic Modulation of Dihydrogen Activation Through Rational Ligand Design in GeII-Ni0 Complexes.

A family of chelating aryl-functionalized germylene ligands has been developed and employed in the synthesis of their corresponding 16-electron Ni0 complexes (PhiPDippGeAr·Ni·IPr; PhiPDipp = {[Ph2PCH2Si(iPr)2](Dipp)N}-; IPr = [{(H)CN(Dipp)}2C:]; Dipp = 2,6-iPr2C6H3). These complexes demonstrate the ability to cooperatively and reversibly activate dihydrogen at the germylene-nickel interface under mild conditions (1.5 atm H2, 298 K). We show that the thermodynamics of the dihydrogen activation process can be modulated by tuning the electronic nature of the germylene ligands, with an increase in the electron-withdrawing character displaying more exergonic ΔG298 values, as ascertained through NMR spectroscopic Van't Hoff analyses for all systems. This is also shown to correlate with experimental 31P NMR and UV/vis absorption data as well as with computationally derived parameters such as Ge-Ni bond order and Ni/Ge NPA charge, giving a thorough understanding of the modulating effect of ligand design on this reversible, cooperative bond activation reaction. Finally, the utility of this modulation was demonstrated in the catalytic dehydrocoupling of phenylsilane, whereby systems that disfavor dihydrogen activation are more efficient catalysts, aligning with H2-elimination being the rate-limiting step. A density functional theory analysis supports cooperative activation of the Si-H moiety in PhSiH3.

Hypervalent Chalcogen Bonds Catalysis on the Intramolecular Aza-Michael Reaction of Aminochalcone: Catalytic Performance and Chalcogen Bond Properties.

Chalcogen bond (ChB) catalysis, as a new type in the field of non-covalent bond catalysis, has become a hot research topic in the field of organocatalysis in recent years. In the present work, we investigated the catalytic performance of a series of hypervalent ChB catalysis based on the intramolecular Aza-Michael reaction of aminochalcone. The reaction includes the carbon-nitrogen bond coupling step (key step) and the proton transfer step. The catalytic performance of mono-dentate pentafluorophenyl chalcogen bond donor ChB1 was comparable to that of bis-dentate chalcogen bond donor ChB4, and stronger than that of mono-dentate chalcogen bond donors ChB2 and ChB3. The formation of the chalcogen bond between the catalyst and the carbonyl oxygen atom of the reactant, causing the charge rearrangement of the reactant and C(1) charge of the -C-Ph group to become more positive, thereby the ChB catalysis promoted the nucleophile reaction. The electron density of the chalcogen bond of the pre-complex, the most positive electrostatic potentials of the catalyst, and the NPA charge of the key atom are proportional to the Gibbs energy barrier of the C-N bond coupling process, which provides an idea to predict the catalytic activity of the ChB catalysis.

Mechanochemical Synthesis of Non-Solvated Dialkylalumanyl Anion and XPS Characterization of Al(I) and Al(II) Species.

A non-solvated alkyl-substituted Al(I) anion dimer was synthesized by a reduction of haloalumane precursor using a mechanochemical method. The crystallographic and theoretical analysis revealed its structure and electronic properties. Experimental XPS analysis of the Al(I) anions with reference compounds revealed the lower Al 2p binding energy corresponds to the lower oxidation state of Al species. It should be emphasized that the experimentally obtained XPS binding energies were reproduced by delta SCF calculations and were linearly correlated with NPA charges and 2p orbital energies.

Electronic Structure and Chemical Bonding of the First-, Second-, and Third-Row-Transition-Metal Monoborides: The Formation of Quadruple Bonds in RhB, RuB, and TcB.

Boron presents an important role in chemistry, biology, and materials science. Diatomic transition-metal borides (MBs) are the building blocks of many complexes and materials, and they present unique electronic structures with interesting and peculiar properties and a variety of bonding schemes which are analyzed here. In the first part of this paper, we present a review on the available experimental and theoretical studies on the first-row-transition-metal borides, i.e., ScB, TiB, VB, CrB, MnB, FeB, CoB, NiB, CuB, and ZnB; the second-row-transition-metal borides, i.e., YB, ZrB, NbB, MoB, TcB, RuB, RhB, PdB, AgB, and CdB; and the third-row-transition-metal borides, i.e., LaB, HfB, TaB, WB, ReB, OsB, IrB, PtB, AuB, and HgB. Consequently, in the second part, the second- and third-row MBs are studied via DFT calculations using the B3LYP, TPSSh, and MN15 functionals and, in some cases, via multi-reference methods, MRCISD+Q, in conjunction with the aug-cc-pVQZ-PPM/aug-cc-pVQZB basis sets. Specifically, bond distances, dissociation energies, frequencies, dipole moments, and natural NPA charges are reported. Comparisons between MB molecules along the three rows are presented, and their differences and similarities are analyzed. The bonding of the diatomic borides is also described; it is found that, apart from RhB(X1Σ+), which was just recently found to form quadruple bonds, RuB(X2Δ) and TcB(X3Σ-) also form quadruple σ2σ2π2π2 bonds in their X states. Moreover, to fill the gap existing in the current literature, here, we calculate the TcB molecule.

Puzzling Structure of the Key Intermediates in Gold(I)-catalyzed Cyclization Reactions of Enynes and Allenenes.

We identify the dominant structures of the intermediates of gold(I)-catalyzed cyclizations of 1,5-enynes and 1,5-allenenes through computational analysis as gold(I) cyclopropylcarbenes, endocyclic vinylgold complexes and previously unreported non-classical carbocationic minima. In contrast to 1,6-enynes, the exocyclic carbocations are found to be less stable. Cyclopropylcarbene structures are consistently favoured as the most stable intermediates for all studied substitution patterns. We validate the computational methods used by using DLPNO-CCSD(T) energies as a benchmark, indicating that the B3LYP-D3 and M06-D3 functionals are most accurate for energy determination, while NPA charges are mostly insensitive to functional. The evolution of a 1,6-enyne in a single-cleavage or double-cleavage rearrangement is attributed to the barrierless evolution of a common cyclopropyl-gold(I) carbocation non-stationary geometry. Our findings provide insights into reaction pathways and substrate dependence of the cycloisomerization processes.

Synthesis, SC-XRD structure, spectroscopy, intermolecular interactions, DFT/TD-DFT investigation, and (static, dynamic) NLO properties of (2E,5Z)-3-(4-fluorophenyl)-2-(4-fluorophenylimino)-5-((E)-3-(2-nitrophenyl) allyliden) thiazolidin-4-one

This paper describes the synthesis of a novel fluorine-substituted thiazolidin-4-one compound, (2E,5Z) -3-(4-fluorophenyl) -2-(4-fluorophenylimino) -5-((E)-3-(2-nitrophenyl) allyliden) thiazolidin-4-one, abbreviated as F2NTh. Its structure was subsequently characterized by Fourier transform infrared (FTIR), 1H and 13C nuclear magnetic resonance (NMR), UV–Visible, and single crystal X-ray diffraction (SC-XRD). For a better comprehension of the electronic structure of F2NTh, experimental data collected from the X-ray diffraction pattern were then compared to theoretical results computed by the density functional theory (DFT) using both B3LYP and CAM-B3LYP functionals with a 6–311 G (d, p) basis set. Theoretical results exhibited a good correlation with those established through the experimental analysis. To identify intra- and intermolecular interactions, Hirshfeld surface (HS) and reduced density gradient (RDG) analyses were performed. The results, including 2D fingerprint plots, indicated that H…H interactions played a major role, accounting for 23.6 % of the overall intermolecular contacts. To investigate the charge transfer and ascertain the electronic properties of F2NTh, frontier molecular orbitals and global and local chemical reactivity descriptors were studied. By simulating the molecular electrostatic potential (MEP) and using MPA, NPA, ESP, and MC5 atomic charges, reactive sites within the molecule responsible for electrophilic and nucleophilic attacks were identified. Some thermodynamic parameters and functions (enthalpy, heat capacity, and entropy) obtained from spectroscopic data were also examined in the temperature range of 100−1000 K. Finally, to test the title molecule in the non-linear optical (NLO) domain, the corresponding properties were predicted using B3LYP and CAM-B3LYP functionals. The predicted static NLO parameters (μ = 4.93 D, α = 56.23×10−24 esu, β = 28×10−30 esu, and γ = 244.98 × 10−36 esu) revealed highly promising outcomes, exhibiting the molecule's utility in NLO applications. This activity was confirmed by the dynamic NLO parameters showing a high third-order response.

Theoretical Investigation on Highly Efficient Quinacridone Derivatives for Green Dopant OLEDs: A DFT Simulation

The present computational work deals with the Quinacridone green dopant theoretical organic light emitting diode molecule has been carried out with density functional theory by using Gaussian09 package. All the quantum chemical calculations have been performed with HF, B3LYP and B3PW91 functional methods. The structural parameter, bond topological analysis and the corresponding electrostatic and transport properties of the OLED molecule has been calculated. The laplacian of electron density and bond ellipticity of molecule have been studied for various optimized methods. The atomic charges of the molecule for different optimized methods has been analysed with AIM, MPA and NPA charges. The HLG of the molecule are calculated from different optimized basis sets. The HF method value is 8.49 eV. The B3LYP and B3PW91 methods energy values are 3.13 eV and 3.12 eV respectively. These values are most equal to the energy gap obtained from density of states (DOS) spectrum. Hence, the ESP shows that expend of O-atoms and the charge accumulated through Quinacridone OLED molecule. The grateful Quinacridone green dopant derivative molecule is high quantum efficiency, longer lifetime and very useful to industrial organic pigment of these molecules.

Effect of Substituent Groups on the Strength of Intramolecular Hydrogen Bonds in 2,4-Dihydroxybenzophenone UV Absorbers

2,4-Dihydroxybenzophenone is the most widely used molecule in the benzophenone group of UV absorbers. It is known that the UV absorption ability is dependent on the substituents. Numerous studies have shown that the strength of intramolecular hydrogen bonds is the main factor affecting this type of UV absorber. However, the effect of substituents on the formation and nature of the hydrogen bonds has not been well studied. In this work, the effect of the type of substituent and the substitution position on the absorption intensity of 2,4-dihydroxybenzophenone molecules is verified both experimentally and theoretically. The effect of substituents on the intramolecular hydrogen bonding of 2,4-dihydroxybenzophenone was investigated by DFT calculations. The results indicate that the addition of different substituents leads to various changes in the strength of the hydrogen bonding in 2,4-dihydroxybenzophenone. On the X-substitution site or the Y-substitution site, halogen groups and electron-absorbing groups such as -CN and -NO2 increase the strength of the hydrogen bond, while electron-giving groups such as -N(CH3)2 and -OCH3 decrease the strength of the bond. For the same substituent, the one at the Y site has a higher effect on hydrogen bonding than that at the X site. By NBO analysis, it was found that the substituents would cause charge redistribution of the individual atoms of 2,4-dihydroxybenzophenones, thus affecting the formation and strength of the hydrogen bonds. Moreover, when the substituent is at the Y substitution site, the oxygen atom of the carbonyl group is less able to absorb electrons and more charge is attracted to the oxygen atom of the hydroxyl group, resulting in a larger charge difference between the two oxygen atoms and an increase of bond energy. Finally, a multiple linear regression analysis of the NPA charge number of the atoms involved in the formation of the hydrogen-bonded chelated six-membered ring was performed with the energy of the hydrogen bond and the percentage of influencing factors estimated, which were found to jointly affect the strength of hydrogen bonding. The aim of this study is to provide theoretical guidance for the design of benzophenone-based UV absorbers that absorb UV light of specific wavelength bands.

Alkali metals doping into open-cage fullerenes: Novel alkalides (M+@C50N5H5)Mʹ− with large nonlinear optical responses

Based on open-cage fullerenes C50N5H5, a novel type of compounds (M+@C50N5H5)Mʹ− (M = Li, Na; Mʹ = Li, Na and K) was designed and studied. Firstly, their alkalides’ properties are confirmed by their FMO and NPA charges analysis. In particular, the proposed alkalides exhibited considerable first hyperpolarizability (β0) up to 1.91 × 105 a.u., which indicated that they could be regarded as high-performance novel NLO molecules. These alkalides will pave the way for further exploration of electronic-stable, high-performance NLO materials.

A quinoline-benzotriazole derivative: Synthesis, crystal structure and characterization by using spectroscopic, DFT and molecular docking methods

In this research, FT-IR, NMR (1H &13C), mass spectrometry and single-crystal X-ray diffraction has been used to characterize the synthesized 5-((1H-benzo[d][1,2,3]triazol-1-yl)methyl)quinolin-8-ol (DD2) derivative. B3LYP calculations with the 6-31G* and 6–311++G** basis sets have shown that the most stable C2 structure in gas phase and aqueous solution is in agreement with the experimental determined by X-ray diffraction. Higher dipole moments for C2 in aqueous solution, predicted with both methods, are probably related to its higher stability resulting higher volume contraction (ΔV −1.0 Å3) in solution with the B3LYP/6-31G* method. Similar behaviours in the Mulliken and NPA charges but different from MK charges are observed. Bond orders studies reveal that the O15-H16···N17 bonds are present in both media, as was experimentally observed in the solid state. MEP surfaces have evidenced nucleophilic sites on N of triazol ring while weak electrophilic ones on aromatic H of three rings being the H atom of OH the most labile. Gap values support a lower reactivity of C2 in solution, in agreement with the higher stability evidenced by AIM analyses. The higher electronic density on triazol ring could justify that C2 is unstable in solution, as revealed by NBO analyses. Complete assignments of 93 expected vibration normal modes of C2 and a set of scaled force constants were obtained in both media by using harmonic force fields. Comparisons between experimental and theoretical infrared and 1H- and 13C NMR spectra show reasonable concordances. Intermolecular interactions in the crystal packing of DD2 were studied by using Hirshfeld surface analysis. Furthermore, DD2 was investigated against two targets of SARS-CoV-2 (PDB ID: 6WCF and PDB ID: 6Y84) by using molecular docking studies. Finally, drug likeness and ADME properties of DD2 were researched and compared with hydroxychloroquine, remdesivir, oseltamivir, lopinavir, ritonavir molecules associated as SARS-CoV-2 inhibitors.

Mechanistic study on the formation of the alkyl acrylates from CO2, ethylene and alkyl iodides over nickel-based catalyst.

The catalytic conversion of carbon dioxide (CO2) and olefins into acrylates has been a long standing target, because society attempts to synthesize commodity chemicals in a more economical and sustainable fashion. In this work, two alkylation reaction pathways were investigated to explore the role of methylene linkage (-CH2-) on the formation of alkyl acrylate from coupling of CO2 and ethylene, catalyzed by a nickel catalyst in the presence of different alkyl iodides. The energy barrier of Ni-O bond cleavage decreases with increasing methylene linkage of alkyl iodides, which may be due to NPA charge transfer of alkyl iodides. Meanwhile, the O1 (ester sp3 O atom) attack route leading to the formation of alkyl acrylate competes with the O2 (carboxylic sp2 O atom) attack route in terms of energy barriers. Further studies on the fluoro-substituted alkyl acrylates show that neither CF3I nor CF3CH2I is effective in releasing trifluoroalkyl acrylates from the nickellacycle, which explains why only negligible amounts of the desired product were detected in the experiment. In addition, we investigated the non-productive pathways leading to byproducts, such as propionic acid, propionates and ion pair complexes, etc. By comparing the results obtained with CH3I, the use of C2H5I as an electrophilic reagent may stabilize the non-productive intermediates. The methylene linkage has little effect on the main productive pathway. However, it has a significant influence on the side reactions, which is detrimental to the formation of alkyl acrylate in competing with the main productive pathway.

Unraveling photo-induced proton transfer mechanism and proposing solvent regulation manner for the two intramolecular proton-transfer-site BH-BA fluorophore

To expound specific excited state processes of the novel excitation wavelength dependent emission BH-BA fluorophore for better subsequent applications, this wok mainly focus on exploring photo-induced hydrogen bonding geometrical changes, excited state intramolecular proton transfer (ESIPT) mechanism and related regulated behavior via solvent polarity. The differences of structural parameters, infrared (IR) vibrational spectra, core-valence bifurcation (CVB) index as well as electronic densities ρ(r) between S0 and S1 states related to dual hydrogen bonds (O1-H2···N3 and O4-H5···N6) reveal S1-state hydrogen bonding strength facilitate ESIPT behaviors for BH-BA system. Of particular note, O4-H5···N6 plays a more dominant role. Photo-induced intramolecular charge transfer (ICT) and variations of Hirshfled and NPA charges over atoms related to hydrogen bonding moieties promote the ESIPT tendency for BH-BA. Combined potential energy surfaces (PESs), transition state (TS) and intrinsic reaction coordinate (IRC) paths, we illustrate the excited state intramolecular single proton transfer (ESISPT) mechanism of BH-BA should occur along with O4-H5···N6 hydrogen bonding wire, which could be adjusted by surrounding solvent polarity.

Structural growth, stability and electronic characteristics of Al-Sc clusters

Al-Sc alloys that are important and interesting industry materials have recently attracted attention, largely owing to their high-strength properties. In comparison, there are only two reports of the Al-Sc clusters currently available through the Google Scholar. Here, structure characteristics, stability and electronic properties of (AlSc)n (n = 1–9) and (Al3Sc)m (m = 1–5) clusters are investigated using the GA-DFT method. It is found that the Al-Sc clusters prefer compact configurations, involving singlet and triplet states, where Al atoms grow together more easily Sc atoms. Among them, the highly symmetric C2v structure is the very stable for the (AlSc)3 cluster. The AIMD simulations show that the (AlSc)3 cluster still has a good thermal stability at 700 K. The molecular orbitals reveal that the 18 valence electrons of the (AlSc)3 cluster fill shell orbitals resulting in an electron configuration of 1S21P61D82S2. The total density of states of the (AlSc)3 cluster comes from joint contributions of Al and Sc atoms. The NPA charge analysis shows that the charge transfer occurs from the Sc to Al atoms in the cluster. Moreover, the IR and Raman spectroscopy are obtained to manifest structure details of the cluster. It is hoped that our work can further provide beneficial inferences for the study of larger sized Al-Sc clusters in the future.

Theoretical exploration on structures, bonding aspects and molecular docking of α-aminophosphonate ligated copper complexes against SARS-CoV-2 proteases.

Recent years have witnessed a growing interest in the biological activity of metal complexes of α-aminophosphonates. Here for the first time, a detailed DFT study on five α-aminophosphonate ligated mononuclear/dinuclear CuII complexes is reported using the dispersion corrected density functional (B3LYP-D2) method. The electronic structures spin densities, FMO analysis, energetic description of spin states, and theoretical reactivity behaviour using molecular electrostatic potential (MEP) maps of all five species are reported. All possible spin states of the dinuclear species were computed and their ground state S values were determined along with the computation of their magnetic coupling constants. NBO analysis was also performed to provide details on stabilization energies. A molecular docking study was performed for the five complexes against two SARS-CoV-2 coronavirus protein targets (PDB ID: 6LU7 and 7T9K). The docking results indicated that the mononuclear species had a higher binding affinity for the targets compared to the dinuclear species. Among the species investigated, species I showed the highest binding affinity with the SARS-CoV-2 Omicron protease. NPA charge analysis showed that the heteroatoms of model species III had a more nucleophilic nature. A comparative study was performed to observe any variations and/or correlations in properties among all species.

Stabilizing the C−N Double Bond Character in Fumaramide with the Aid of Superacids

AbstractFumaramide was reacted with the superacidic systems XF/SbF5 and XF/BF3 (X=H, D) leading to the formation of the O‐diprotonated species. Using an equimolar amount of the Lewis acids relating to fumaramide, a mixture of the diprotonated salt and the diadduct with O‐coordinated HF was obtained. The salts [C4H2X6N2O2]2+[(BF4)−]2 and [C4H2X6N2O2]2+[(SbF6)−]2 (X=H, D) were characterized by low‐temperature vibrational spectroscopy. Single‐crystal X‐ray structure analyses were carried out for the compounds [C4H8N2O2]2+[(BF4)−]2, C4H6N2O2⋅⋅⋅2HF, and fumaramide. To discuss the experimental results, quantum chemical calculations were executed at the B3LYP/aug‐cc‐pVTZ level of theory. To investigate the impact of the protonation on the resonance +M effect and the electron distribution concerning the conjugated system ESP maps, NPA charges, and NBO analyses were consulted. Due to the protonation, the nitrogen lone pair contributes completely to the formation of the C=N π‐bond, stabilizing the C=N double bond character. Since no monoprotonation of fumaramide is observed, amide hydrolysis is possible simultaneously on both amide groups.

Dual modification to stabilize Non-IPR C72 fullerene: A new theoretical strategy

The stabilization of non-IPR fullerenes for their isolation and characterization is an area of recent interest. In the present study, we have explored the stabilization techniques of C72 isomers via endo and exo-modifications and finally approached dual modification. A total of four isomers of C72 have been considered in this study; among them, one is IPR derivative (1), and the rest are non-IPR derivatives with one (2) and two (3 and 4) fused pentagon rings. First, we have studied the endohedral modification by encapsulating one and two La atoms in the C72 cavity. Secondly, we have exohedrally modified the C72 isomers via chlorination by adding four and eight chlorides, respectively. Our final approach is to study the dual modification, where we have implemented both endo exo-modifications together. This dual modification can be achieved in two ways: exo followed by endo and endo followed by exo. For each modification, the relative stability of every modified C72 derivative has been checked by calculating the relative energy with respect to the most stable modified analogue. To find out whether these modifications are energetically feasible or not, we have calculated the binding energy of each modified C72 isomer. The binding energy calculation reveals that the encapsulation and exo-modification techniques are good enough to stabilize the non-IPR C72 derivatives. Moreover, the effectiveness of dual modification has also been established from the enhanced binding energy compared to either endo- or exo-modification. We have also studied the NPA charges on the encapsulated La atoms for each endo- and dual-modified C72 derivative. Furthermore, the AIM study has also been perceived to find out the interaction between the La atom and the fullerene cages for both mono- and di-encapsulated fullerene derivatives and also between La–La centres for di-encapsulated derivatives. Overall, the present theoretical study will provide an idea about the stability of the modified C72 derivatives, which will help the experimentalists to design new strategies for synthesizing modified non-IPR fullerene derivatives that have vast applications in the medicinal and industrial fields.

Theoretical approach for Fe(II/III) and its chlorophyll-related complexes as sensitizers in dye-sensitized solar cells

Dye is the key to the efficiency of harvesting solar energy in dye-sensitized solar cells (DSSCs). The dye performances such as light absorption, electron injection, and electron regeneration depend on the dye molecule structure. To predict it, one needs to compute the optimized molecule geometry, HOMO level, LUMO level, electron density distribution, energy gaps, and dipole moment in the ground and excited state. Chlorophyll-related chlorin and porphyrin, as well as their κ2O,O’ complexes with Fe(II/III), were investigated with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) computations using the B3LYP method and def2-TZVP basis set. NPA charges also were calculated to know the valence of the metal cations exactly. In general, the calculations show that the metal cations introduced occupied d orbitals with lower oxidation potentials than the chlorophyll ligand orbitals, which are responsible for the emergence of additional absorption bands. The states result in effective band broadening and the redshift of spectrum absorbance that is expected to improve DSSC performance.
 Another requirement that has to be possessed is the ability of electron regeneration, electron injection, and dipole moment. The Fe(II) complex has fulfilled these requirements, but not the Fe(III) complex due to having a low electron injection capability. However, this work has shown that Fe(III) complex exhibits a non-innocence ligand. It results in trivalent to divalent state change, in the appearance of a ligand radical cation, an extra hole, and a broader absorption spectrum. It also can affect its other electronic properties, such as electron injection capability. Thus, it can be considered an attractive candidate for the sensitizer in DSSCs