HOMO-LUMO Gap Research Articles

Investigating the Impact of Packing and Environmental Factors on the Luminescence of Pt(N^N^N) Chromophores.

Four Pt(II)(N^N^N) compounds featuring DMSO coordination at the fourth position were synthesized. Ligands varied in terms of pyridyl central ring (hydrogen/chlorine substituent) and lateral rings (triazoles with CF3 substitution or tetrazoles). Coordination to pyridine yielded tetra-nitrogen coordinated Pt(II) complexes or Pt-functionalized polymers using commercial 4-pyridyl polyvinyl (PV) or dimethylaminopyridine. Luminescence behaviors exhibited remarkable environmental dependence. While some of the molecular compounds (tetrazole derivatives) in solid state displayed quenched luminescence, all the polymers exhibited 3MMLCT emission around 600 nm. Conversely, monomer emission was evident on poly(methyl methacrylate) or polystyrene matrices. DFT calculations were used to analyze the aggregation of the complexes both at the molecular level and coordinated to the PV polymer and their influence on the HOMO-LUMO gaps.

Machine Learning Models for Predicting Zirconocene Properties and Barriers.

Zr metallocenes have significant potential to be highly tunable polyethylene catalysts through modification of the aromatic ligand framework. Here we report the development of multiple machine learning models using a large library (>700 systems) of DFT-calculated zirconocene properties and barriers for ethylene polymerization. We show that very accurate machine learning models are possible for HOMO-LUMO gaps of precatalysts but the performance significantly depends on the machine learning algorithm and type of featurization, such as fingerprints, Coulomb matrices, smooth overlap of atomic positions, or persistence images. Surprisingly, the description of the bonding hapticity, the number of direct connections between Zr and the ligand aromatic carbons, only has a moderate influence on the performance of most models. Despite robust models for HOMO-LUMO gaps, these types of machine learning models based on structure connectivity type features perform poorly in predicting ethylene migratory insertion barrier heights. Therefore, we developed several relatively robust and accurate machine learning models for barrier heights that are based on quantum-chemical descriptors (QCDs). The quantitative accuracy of these models depends on which potential energy surface structure QCDs were harvested from. This revealed a Hammett-type principle to naturally emerge showing that QCDs from the π-coordination complexes provide much better descriptions of the transition states than other potential-energy structures. Feature importance analysis of the QCDs provides several fundamental principles that influence zirconocene catalyst reactivity.

Polysulfide Anions [Sx]2- (x=2, 3, 4, 5): Promising Functional Building Units for Infrared Nonlinear Optical Materials.

Infrared nonlinear optical (IR NLO) materials play significant roles in laser technology. The novel functional building units (FBUs) are of great importance in constructing NLO materials with strong second harmonic generation (SHG). Herein, polysulfide anion [Sx]2- (x=2, 3, 4, 5) units are investigated on NLO-related properties and structure-performance relationships. Theoretical calculations uncover that the [Sx]2- (x=2, 3, 4, 5) units are potential IR NLO FBUs with large polarizability anisotropy (δ), hyperpolarizability (β) and wide HOMO-LUMO gap. Fourteen crystals including [Sx]2- (x=2, 3, 4, 5) units are calculated and analyzed. The results show that these units can result in a wide IR transmittance range, significant SHG effects, wide band gap Eg (Na2S4: Eg=3.09eV), and large birefringence Δn [BaS3 (P21212): Δn=0.70]. More importantly, it is highlighted that the crystal materials including with [Sx]2- (x=2, 3, 4, 5) groups are good candidates for the exploration of the outstanding IR NLO materials.

Bis(diphenyl)phosphinomethane Platinum(II) complex of 1-(benzo[d]thiazol-2-yl)-3-phenylthiourea: Crystal structure and DFT study

This study extensively describes synthesizing and characterizing a novel Pt(II) thiourea complex and its mixed ligand bisdiphenylphosphinomethane complex. The first complex [Pt(BtztH)2] is obtained by reacting K2PtCl4 and 1-(benzo[d]thiazol-2-yl)-3-phenylthiourea in 1:2 molar ratio. The second complex [Pt(Btzt)(dppm)] was synthesized by reacting dichlorobis(diphenyl)phosphinomethane platinum(II) complex with 1-(benzo[d]thiazol-2-yl)-3-phenylthioure in equimolar ratio with the presence of Et3N. Both complexes adopt square planar geometry, which were determined by FT-IR, 1H-nmr and X-ray crystallography. In comparison with the first complex, the second complex has doubly deprotonated, resulting in a dianion Pt(II) complex, which was determined by X-ray single crystal measurement. The asymmetric unit contained two unique molecules with distorted square planar geometry. A couple of non-covalent or intermolecular interactions stabilized the solid-state supramolecular assembly. Hirshfeld surface analysis was conducted in order to have a deeper understanding of the supramolecular assembly. Enrichment ratio calculations determined the pair of chemical species with the highest propensity for making interatomic contact. The [Pt(Btzt)(dppm)] compound was also investigated theoretically. The DFT study was performed by using B3LYP/Def2-TZVP method. Theoretical findings indicate that the HOMO-LUMO gaps range from 2.2 to 3.22 eV, indicating that the compounds possess favorable semiconductor properties. Within these complexes, the coordinated atoms exhibit strong electron donations to the Pt cation, while the Pt cation demonstrates significant back-donation to the ligand.

On-surface synthesis and characterization of polyynic carbon chains.

Carbyne, an elusive sp-hybridized linear carbon allotrope, has fascinated chemists and physicists for decades. Due to its high chemical reactivity and extreme instability, carbyne was much less explored in contrast to the sp2-hybridized carbon allotropes such as graphene. Herein, we report the on-surface synthesis of polyynic carbon chains by demetallization of organometallic polyynes on the Au(111) surface; the longest one observed consists of ∼60 alkyne units (120 carbon atoms). The polyynic structure of carbon chains with alternating triple and single bonds was unambiguously revealed by bond-resolved atomic force microscopy. Moreover, an atomically precise polyyne, C14, was successfully produced via tip-induced dehalogenation and ring-opening of the decachloroanthracene molecule (C14Cl10) on a bilayer NaCl/Au(111) surface at 4.7K, and a band gap of 5.8eV was measured by scanning tunnelling spectroscopy, in a good agreement with the theoretical HOMO-LUMO gap (5.48eV).

Controlling aggregation of diketopyrrolopyrroles in water

Charge repulsion can be used to control and fine tune the supramolecular aggregation of amino acid substituted diketopyrrolopyrroles in water. This is a simple method to access a number of different aggregation states with distinct photophysical properties without the need for extensive synthetic tuning, process engineering, or solvent optimisation. Most importantly, these different aggregates show different optical gaps, HOMO-LUMO gaps, electroactivity, and exciton binding energies. These systems expand the absorbance range achieved from one chromophore unit and also create systems with large Stokes shifts. This work therefore answers the demand for tailoring aggregate structures by manipulating charge repulsion in an aqueous environment.

First-principles study of imine bond formation energies of aldehyde isomers

A first-principles approach was taken to study the structure, energy, and reaction coordinates of imine bonds involving Jeffamine EDR-148 and three phthalaldehyde isormers, o-phthalaldehyde (o-PA), m-phthalaldehyde (m-PA), and p-phthalaldehyde (p-PA). The electronic structure and spatial distribution of states was reported. From the computed electronic structure, relevant parameters including the ionization and affinity energies, HOMO-LUMO gap, and hardness were determined. The role of electronic structure on the stability and bonding pathways was presented.

COMPAS-2: a dataset of cata-condensed hetero-polycyclic aromatic systems

Polycyclic aromatic systems are highly important to numerous applications, in particular to organic electronics and optoelectronics. High-throughput screening and generative models that can help to identify new molecules to advance these technologies require large amounts of high-quality data, which is expensive to generate. In this report, we present the largest freely available dataset of geometries and properties of cata-condensed poly(hetero)cyclic aromatic molecules calculated to date. Our dataset contains ~500k molecules comprising 11 types of aromatic and antiaromatic building blocks calculated at the GFN1-xTB level and is representative of a highly diverse chemical space. We detail the structure enumeration process and the methods used to provide various electronic properties (including HOMO-LUMO gap, adiabatic ionization potential, and adiabatic electron affinity). Additionally, we benchmark against a ~50k dataset calculated at the CAM-B3LYP-D3BJ/def2-SVP level and develop a fitting scheme to correct the xTB values to higher accuracy. These new datasets represent the second installment in the COMputational database of Polycyclic Aromatic Systems (COMPAS) Project.

Screening novel candidates of ZL003-based organic dyes for dye-sensitized solar cells by modifying auxiliary electron acceptors: A theoretical study

In this work, a series of ZL003-based free-metal sensitizers with the donor-acceptor-π- conjugated spacer-acceptor (D-A-π-A) structure were designed by modifying auxiliary electron acceptors for the potential application in dye-sensitized solar cells. The energy levels of frontier molecular orbitals, absorption spectra, electronic transition, and photovoltaic parameters for all studied dyes were systematically evaluated using density functional theory (DFT)/time-dependent DFT calculations. Results illustrated that thienopyrazine (TPZ), selenadiazolopyridine (SDP), and thiadiazolopyridine (TDP) are excellent electron acceptors, and dye sensitizers functionalized by these acceptors have smaller HOMO-LUMO gaps, obviously red-shifted absorption bands and stronger light harvesting. The present study revealed that the photoelectric conversion efficiency (PCE) of ZL003 is around 13.42 % with a JSC of 20.21 mA·cm−2, VOC of 966 mV and FF of 0.688 under the AM 1.5G sun exposure, in good agreement with its experimental value (PCE = 13.6 ± 0.2 %, JSC = 20.73 ± 0.20 mA·cm−2, VOC = 956 ± 5 mV, and FF = 0.685 ± 0.005.). With the same procedure, the PCE values for M4, M6, and M7 were estimated to be as high as 19.93 %, 15.38 %, and 15.80 % respectively. Hence, these three dyes are expected to be highly efficient organic sensitizers applied in practical DSSCs.

Stability and Electronic Properties of Mixed Rare-Earth Tri-Metallofullerenes YxDy3-x@C80 (x = 1 or 2).

Tri-metallofullerenes, specifically M3@C80 where M denotes rare-earth metal elements, are molecules that possess intriguing magnetic properties. Typically, only one metal element is involved in a given tri-metallofullerene molecule. However, mixed tri-metallofullerenes, denoted as M1xM23-x@C80 (x = 1 or 2, M1 and M2 denote different metal elements), have not been previously discovered. The investigation of such mixed tri-metallofullerenes is of interest due to the potential introduction of distinct properties resulting from the interaction between different metal atoms. This paper presents the preparation and theoretical analysis of mixed rare-earth tri-metallofullerenes, specifically YxDy3-x@C80 (x = 1 or 2). Through chemical oxidation of the arc-discharge produced soot, the formation of tri-metallofullerene cations, namely Y2Dy@C80+ and YDy2@C80+, has been observed. Density functional theory (DFT) calculations have revealed that the tri-metallofullerenes YxDy3-x@C80 (x = 1 or 2) exhibit a low oxidation potential, significantly lower than other fullerenes such as C60 and C70. This low oxidation potential can be attributed to the relatively high energy level of a singly occupied orbital. Additionally, the oxidized species demonstrate a large HOMO-LUMO gap similar to that of YxDy3-xN@C80, underscoring their high chemical stability. Theoretical investigations have uncovered the presence of a three-center two-electron metal-metal bond at the center of Y2DY@C80+ and YDy2@C80+. This unique multi-center bond assists in alleviating the electrostatic repulsion between the metal ions, thereby contributing to the overall stability of the cations. These mixed rare-earth tri-metallofullerenes hold promise as potential candidates for single-molecule magnets.

Synthesis, crystal structure investigation, and theoretical approaches to discover potential 6-bromo-3-cyanocoumarin as a potent inhibitor MetAP (methionine aminopeptidase) 2

It has been ascertained that trifluoroacetic acid accelerates the Knoevenagel condensation reaction of 5-bromosalicylaldehyde and ethyl ester of cyanoacetic acid. As a result, the 6-bromo-3-cyanocoumarin compound has been synthesized and the structure was eventually confirmed by X-ray analysis. Based on the structure-activity relationship and literature survey we found this compound has a potent inhibitor for MetAP (methionine aminopeptidase) and further we have studied molecular docking to understand the binding interactions and also performed ADME/T studies for this compound. The surface reactivity and intermolecular interactions of the studied compound were investigated by Hirshfeld surface analysis. Energy framework analysis shows the interaction between pair of fragments with neighbor molecules. Furthermore, the DFT study is performed to investigate structural reactivity and stability at B3LY/6-311+G(d,p) functional. The decreased HOMO-LUMO gap (3.97 eV) indicates its higher reactivity and soft nature. Molecular electrostatic potential (MESP) analysis and NBO charges indicate the structure's reactive site and charge transfer. Excited analysis by using the TD-DFT was performed to get excitation energy (ΔE), absorbance, and oscillator strength (fo) of crucial transition. Theoretically predicted values of polarizability (αo) and hyperpolarizability (βo) suggest their excellent optical and Nnar (NLO) properties.

Electronic Properties of Poly(N-vinylcarbazole) Using semi-empirical oligomer extrapolation approximations

Poly(N-vinylcarbazole) has been widely used in polymer light emitting diodes due to its unique electronic properties. The electronic properties of Poly(N-vinylcarbazole) were examined using the Semi-Empirical Zerner Modified Intermediate Neglect of Differential Overlap (ZINDO) oligomer extrapolation method. In this calculation, the electronic properties of Poly(N-vinylcarbazole) were extracted from oligomer electronic properties. We identified a tendency for oligomers with large HOMO-LUMO gaps in the form of linear regression as function of reciporocal of monomeric units. The increasing number of monomers induce the interaction between energy levels of each monomer which boardening the energy levels. The localized molecular orbital and vibration spectra of the basic unit of polymer Poly(N-vinylcarbazole) also has been investigated.

Topological characterization of cove-edged graphene nanoribbons with applications to NMR spectroscopies

Graphene nanoribbons (GNRs) have recently garnered significant attention due to their potential applications in transistors, photovoltaics, and quantum electronic devices. Cove-edged graphene nanoribbons (CGNRs) are particularly intriguing due to their unique electromagnetic properties. These nanoribbons, characterized by asymmetric edges composed of alternating hexagons, exhibit exceptional electronic properties. In this study, we employed a variety of degree and degree-sum-based topological descriptors (TDs) to calculate the topological entropy measures of CGNRs. The explicit mathematical formulae of the TDs for the CGNRs were derived using the edge partition method. Additionally, we determined the spectral diameters, delocalization energies, resonance energies, and HOMO-LUMO gaps to assess these compounds' thermodynamic and kinetic stabilities. We also utilized NEWGRAPH and MATLAB software to predict the NMR patterns for the CGNRs. The shallow HOMO-LUMO gaps in these calculations suggest that CGNRs are promising candidates for topological spintronics applications.

Synthesis of Tridecacene by Multistep Single-Molecule Manipulation.

Acenes represent a unique class of polycyclic aromatic hydrocarbons that have fascinated chemists and physicists due to their exceptional potential for use in organic electronics. While recent advances in on-surface synthesis have resulted in higher acenes up to dodecacene, a comprehensive understanding of their fundamental properties necessitates their expansion toward even longer homologues. Here, we demonstrate the on-surface synthesis of tridecacene via atom-manipulation-induced conformational preparation and dissociation of a trietheno-bridged precursor on a Au(111) surface. The generated tridecacene has been investigated by scanning tunneling microscopy and spectroscopy (STM/STS), combined with first-principles calculations. We observe that the STS transport gap (1.09 eV) shrinks again following the gap reopening of dodecacene (1.4 eV). Spin-polarized density functional theory calculations confirm an antiferromagnetic open-shell ground-state electronic configuration for tridecacene in the gas phase. Interestingly, tridecacene's open-shell character is significantly reduced upon interaction with the Au(111) surface despite being only physisorbed. The interaction with the surface leads to a lowering of the magnetization of tridecacene, a reduced gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), compared to the gas phase, and a reduced relative energy to the nonmagnetic state, making it nearly isoenergetic. These observations show qualitatively that the influence of the Au(111) substrate on the properties of long acenes is significant, which is important for interpreting the measured STS transport gaps. Our work contributes to a fundamental understanding of the electronic properties of long acenes, confirming a nonmonotonous length-dependent HOMO-LUMO gap, and to the development of multistep tip-assisted synthesis of elusive compounds.

Theoretical investigation of red-shifted emission of graphitic boron doping in graphene quantum dots

Graphene quantum dots (GQDs) are promising as luminescent materials in wide fields of applications. However, the narrow emission only at visible region restricts their further development. In this work, graphitic boron doping in GQDs have been theoretically investigated which yield red-shift emission of GQDs to NIR-MIR region. Calculated results reveal that both BC2 and BC3 bonding would narrow HOMO-LUMO gaps which achieve redshift of emission from 482 nm to 5619 nm. Moreover, for multiple B atoms doped GQDs containing both BC2 and BC3, these two bonding structures exhibit opposite trends: BC2 only dominates electron distribution at HOMO energy level while BC3 only dominates LUMO. Furthermore, geometrical distortion introduced by B-doping shows less impact on electronic and optical properties of GQD. This work reveals the mechanism of BC2 and BC3 bonding affecting electronic and optical properties and provides approaches to achieve red-shifted emission in NIR region of GQDs with considerable emission efficiency.

Molecular level interaction, electrons excitation properties, solvent effect using IEFPCM investigation, topological surface, and docking analysis of 4-pyrrolidin-2-yl-pyridine

Abstract Optimisation of molecular geometry of the headline compound, 4-pyrrolidin-2-yl-pyridine (4P2YLP) was achieved theoretically exercising Density Functional Theory using B3LYP standard approach utilising basis set, 6-311++G(d,p). Using Gaussian 09, HOMO–LUMO analysis was achieved to comprehend the chemical activity and electronic properties of the heading compound. The least HOMO–LUMO gap was obtained for gas phase (5.6486). Bonding interlinkage of the fragments is accomplished by Natural Bonding Orbitals (NBO), as steadiness and chemical reactivity depend on the border molecular orbitals. The nucleophilic & electrophilic spots along with 3D charge transmission areas are determined using the Molecular Electrostatic Potential (MEP). Multiwfn 3.8 software with Pauli Repulsion (PR) & electron localization has been used to conduct ELF and LOL research. While LOL simply displays the most closely spaced orbitals overlapping, ELF displays the electron pair density. Non-linear response properties are analysed in a variety of solvents. The dipole moment (1.9039), polarizability (3.23017E-23 esu) & first order hyperpolarizability (1.51981E-30 esu) of water are the highest values among the selected solvents. Different solvents endured UV–Vis analysis employing TD-DFT technique and the absorption of maximum wavelength is accomplished. Fructose 5-dehydrogenase inhibitor activity by docking is investigated using molecular modelling procedures.

Determination of Ground State Structures of Snx - (x=21-35) Clusters.

In this work, an unbiased global search with a homemade genetic algorithm was performed to investigate the structural evolution and electronic properties of Snx - (x=21-35) clusters with density functional theory (DFT) calculations. All the ground-state structures for all these Snx - (x=21-35) clusters have been confirmed by the comparison of the experimental and simulated photoelectron spectra (PESs). It has been revealed that all Snx - (x=21-35) clusters are tricapped trigonal prism (TTP)-based structures consisting of two (for sizes x=21-28) or three (for x=29-35) TTP units, with the remaining atoms adsorbed on the surface or inserted between TTP units. The gradually decreasing HOMO-LUMO gaps indicate that these clusters are undergoing semiconductor-to-metal transformation. The average binding energies show that the structural stabilities of Snx - clusters are not as good as that of silicon and germanium clusters. It found that sizes x=23, 25, 29, 33 show high relative stability.

Synthesis, crystal structure, exploration of the supramolecular assembly through Hirshfeld surface analysis of new 2,4-dihydro-1H-1,2,4-triazole-3-selones and 3,3′-di(4H-1,2,4-triazolyl)diselenides

The reaction of aromatic ring-substituted isoselenocyanates with 2-thiopheacetic and 4-pyridinecarboxylic acid hydrazides yielded selenosemicarbazides, which were further converted into previously unknown 1,2,4-triazole-3-selones and 3,3′-di(4H-1, 2,4-triazolyl)diselenides. The structure of the obtained compounds was studied by X-ray diffraction analysis and NMR spectroscopy. Theoretically, the reactivity and nonlinear optical (NLO) properties were predicted by using the DFT-B3LYP method. Charge separation and orbital analysis were performed by using the frontier molecular orbital (FMO) and natural population analysis (NPA). 5aa, 5ca, and 5ab show significantly reduced HOMO-LUMO gaps and ionization potential (IP) among the other compounds. The density of states (DOS) spectra was plotted to get a pictorial representation of orbital and their energies. The highest βo value of 1754.31 au is obtained for 7fb which is indicating its excellent NLO properties. Nature and strength of Intermolecular interactions in crystal packing is considered through Hirshfeld surface (HS) analysis using the CrystalExplorer. Hence, the studied compounds have significant reactivity and NLO properties and may open a new door in searching for new NLO materials.

Computational investigations of different iron oxide–coronene nanoclusters: a DFT study

Abstract This study utilizes density functional theory (DFT) to investigate the adsorption of iron oxide clusters on the surface of coronene nanocages. The study explores five different adsorption geometries (P1–P5) using the B3PW91/6-311G (d, p) approach, comparing them to pure coronene. Electronic properties, including energy (hf), HOMO, LUMO, Fermi level, HOMO–LUMO gap, vertical ionization potential, electron affinity, chemical hardness, softness, and chemical potential, were analyzed compared to native coronene nanocages. The calculations revealed strong chemisorption in P1, attributed to significant charge transfer from coronene to the metal atom, resulting in altered positions of HOMOs and LUMOs and a reduced HOMO–LUMO gap (E gap). Across all geometries (P1–P5), electronic densities in HOMOs were concentrated on iron oxides, while in LUMOs, the electronic cloud was distributed throughout the structure. The diffusion of d-electrons from iron contributed to a more diffuse structure and a lower HOMO–LUMO gap (E gap), indicating N-type conduction. Global indices demonstrated increased reactivity of iron oxide–adsorbed coronene nanocages compared to native, unbound coronene.

Synthesis, optical, electrochemical, and computational study of benzene/thiophene based D-π-A chromophores.

We report the design, synthesis, electrochemical, UV-vis, fluorescence, and computational study of nine π-linked donor-acceptor (D-π-A) chromophores. The series of novel compounds comprises a terphenyl, terthiophene, or 2,5-diphenyl thiophene linker, with one electron-donating group (methyl or p-N,N-diethyl) and one electron-withdrawing group (nitrone, formyl, or dicyanovinyl) at opposite ends of the molecule. The HOMO-LUMO gaps were determined via cyclic voltammetry and found to correspond well to DFT-calculated values. Furthermore, the influence of the π-linker character and substituent on the HOMO-LUMO gap was analysed and interpreted in terms of MO composition via DFT.