HOMO-LUMO Gap Research Articles

Exo‐6b2‐Methyl‐Substituted Pentabenzocorannulene: Synthesis, Structural Analysis, and Properties

Abstractexo‐6b2‐Methyl‐substituted pentabenzocorannulene (exo‐PBC‐Me) was synthesized by the palladium‐catalyzed cyclization of 1,2,3‐triaryl‐1H‐cyclopenta[l]phenanthrene. Its bowl‐shaped geometry with an sp3 carbon atom in the backbone and a methyl group located at the convex (exo) face was verified by X‐ray crystallography. According to DFT calculations, the observed conformer is energetically more favorable than the endo one by 39.9 kcal/mol. Compared to the nitrogen‐doped analogs with intact π‐conjugated backbones (see the main text), exo‐PBC‐Me displayed a deeper bowl depth (avg. 1.93 Å), redshifted and broader absorption (250–620 nm) and emission (from 585 to more than 850 nm) bands and a smaller optical HOMO–LUMO gap (2.01 eV). exo‐PBC‐Me formed polar crystals where all bowl‐in‐bowl stacking with close π ⋅ ⋅ ⋅ π contacts is arranged unidirectionally, providing the potential for applications as organic semiconductors and pyroelectric materials. This unusual structural feature, molecular packing, and properties are most likely associated with the assistance of the methyl group and the sp3 carbon atom in the backbone.

Exo-6b2-Methyl-Substituted Pentabenzocorannulene: Synthesis, Structural Analysis, and Properties.

exo-6b2-Methyl-substituted pentabenzocorannulene (exo-PBC-Me) was synthesized by the palladium-catalyzed cyclization of 1,2,3-triaryl-1H-cyclopenta[l]phenanthrene. Its bowl-shaped geometry with an sp3 carbon atom in the backbone and a methyl group located at the convex (exo) face was verified by X-ray crystallography. According to DFT calculations, the observed conformer is energetically more favorable than the endo one by 39.9 kcal/mol. Compared to the nitrogen-doped analogs with intact π-conjugated backbones (see the main text), exo-PBC-Me displayed a deeper bowl depth (avg. 1.93 Å), redshifted and broader absorption (250-620 nm) and emission (from 585 to more than 850 nm) bands and a smaller optical HOMO-LUMO gap (2.01 eV). exo-PBC-Me formed polar crystals where all bowl-in-bowl stacking with close π ⋅ ⋅ ⋅ π contacts is arranged unidirectionally, providing the potential for applications as organic semiconductors and pyroelectric materials. This unusual structural feature, molecular packing, and properties are most likely associated with the assistance of the methyl group and the sp3 carbon atom in the backbone.

(Invited) Is the [5,5] C120-D5d Fullertube a Metal?

Single-walled nanotubes (SWNTs) with a roll-up vector (n = m) have long been predicted to exhibit metallic behavior at infinite nanotube lengths.1 Moreover, in contrast with normal metals, armchair nanotubes e.g., [5,5] should result in exceptional ballistic transport properties.2 However, the question remains at what finite length of a SWNT or fullertube does metallic character begin, if at all. From a computational viewpoint, Cioslowski has shown that the HOMO-LUMO bandgap decreases to ~1 eV in an oscillatory fashion in approaching [5,5] C200 fullertubes.3 Although the HOMO-LUMO gap has been extensively used to predict the kinetic stability of fullerenes and metallofullerenes with less than 100 carbon atoms, Fowler has argued that the HOMO-LUMO gap can not be used to predict the kinetic stability of large fullerenes.4 More recently, Lilijeroth and coworkers have measured the experimental and DFT HOMO-LUMO gap for graphene nanoribbons (GNR) and find that GNRs with lengths of 5 nm have bandgaps of ~0.1 eV.5 These workers also point out that DFT calculated HOMO-LUMO bandgaps are always overestimated relative to experimental values. In this presentation, I will present the evidence in support of metallic character for [5,5] C120-D5d.6,7

Structural evolution, electronic and optical properties of praseodymium doped silicon cluster PrSin0/- (n = 10–20): A theoretical investigation

The rare earth dope d nano-cluster can be a building block for the next-generation photo-electrical industry, so the imminent discovery of novel, suitable nano-functional material is urgent. Praseodymium element as a wonderful dopant, bestow a novel photoelectrochemical properties for nanomaterials especially for semiconductor, derived from its unfulfilled 4f electrons configuration and active electronic transitions between 4f to 4f and 4f to 5d. In view of this, the neutral and anionic clusters of PrSin0/- with a medium size of n = 10–20 are comprehensively investigated by the quantum chemistry method of mPW2PLYP associated with the global searching potential energy surface techniques. The geometry evolution in medium size for PrSin can be attributed to three stages of replaced (n = 10–12), linked (n = 13–19), and cage (n = 20) structure. For PrSin-, two evolution phases are obviously observed by linked (n = 10–19) and cage (n = 20) structure. The PES spectra of the anionic most stable cluster and several degeneracy structures are simulated to identify the ground state structure. Each cluster of AEA, charge transfer, and VDE values are all calculated. Combined with binding energy, HOMO-LUMO gap, molecular orbital analysis, and a series of optical properties estimated, including simulated UV–vis, IR, and Raman spectra, excitation behavior shows PrSi20- has not only prominent stability but also has a proper range of lighting absorption, higher electron-hole recombination, possible as a functional material for optoelectronic devices.

Three new complexes of Zn(II) with a quinoline based Schiff base ligand: Syntheses, crystal architectures, Hirshfeld surface analyses, DFT study, photoluminescence and thermal properties

This report deals with one dinuclear and two mononuclear zinc(II) complexes of compositions [Zn2L2(μ1,1-N3)(N3)] (1), [ZnL(NCO)(H2O)] (2) and [ZnL(NCS)(H2O)] (3), where HL ((E)-2-ethoxy-6-((quinolin-8-ylimino)methyl)phenol)) is the 1:1 condensation product of 3-ethoxysalicylaldehyde and 8-aminoquinoline. All the three metal complexes have been characterized by C, H, N elemental analyses, FT-IR spectra, single crystal X-ray structures and powder XRD. The structures of 2 and 3 are isomorphous. The metal centres in 1–3 are five coordinated and adopt vacant octahedral or distorted square pyramidal geometry for 1 and distorted trigonal bipyramidal geometry for 2 and 3. Supramolecular interactions and topologies in all the three crystal structures have been analyzed, revealing 3–D assemblies in 1–3 due to a number of non-covalent interactions (C–H···O, C–H···N and π···π in 1; C–H···O, O–H···O, O–H···N, π···π and C–H···π in 2; C–H···S, O–H···O, O–H···N, π···π and C–H···π in 3). To gain additional insight into the intermolecular contacts and their relative contributions towards the packing, Hirshfeld surface analyses have been undertaken for 1–3 and demonstrated in detail with respect to structural parameters, depressions in surfaces, fingerprint plots and enrichment ratios. The thermo-gravimetric and differential thermal analyses (TG/DTA) have been performed and the decomposition patterns are well explained. Steady state and time resolved fluorescence properties have been investigated. Optical band gaps have been determined from the data of the UV–Vis spectra. DFT calculations have been undertaken. The DFT computed HOMO-LUMO gaps corroborate the optical gaps and the DFT computed electrostatic potential (ESP) surfaces rationalize the supramolecular interactions nicely.

Syntheses, characterizations and reactions of acene-2,3-dicarbaldehydes.

Here, we report improved syntheses, detailed characterizations and reactions of a series of acene-2,3-dicarbaldehydes including tetracene-2,3-dicarbaldehyde. DFT calculations corroborate and complement the experimental results. Tetracene-2,3-dicarbaldehyde and the benchmark organic semiconductor pentacene have isoelectronic π-systems and similar HOMO-LUMO gaps. Tetracene-2,3-dicarbaldehyde is soluble in a host of organic solvents (e.g., DMF, toluene, THF, chloroform, dichloromethane) and shows excellent photooxidative resistance in solution phases exposed to light and air. Further, it is readily sublimed from the solid-state without decomposition, and can be functionalized using different chemistries. We have demonstrated the utility of acene-2,3-dicarbaldehydes as reactants in the syntheses of novel α,α'-diaryl-2,3-acenedimethanols and acenotropones via Grignard reactions and double-aldol condensation reactions, respectively. The acenotropones were further reacted with concentrated H2SO4 to generate hydroxyacenotropylium ions that exhibit long wavelength absorption in the visible and near-IR regions. The optical gap measured for hydroxyanthracenotropylium ion is 1.3 eV. The results gained here implicate acene-2,3-dicarbaldehydes as potential high-value organic semiconductors and as precursors to a host of interesting molecules and materials.

Phenyl-urea chromophores: DFT insights into nonlinear optical enhancement

The present investigation has examined the nonlinear optical (NLO) responses of molecules based on phenyl-urea. The optimized geometries of complexes: (4-nitrophenyl) urea (PU1), 1-methyl-3-(4-nitrophenyl) urea (PU2), and 1,1-dimethyl-3-(4-nitrophenyl) urea (PU3) are extracted using M06–2X/6–311++ g (d, p) level of theory. The estimated nonlinear optical responses (NLO) of the compounds given are based on static and dynamic hyperpolarizabilities, which are reinforced by the dipole moment, polarizabilities, global reactivity parameters, HOMO-LUMO gap, molecular electrostatic potentials (MEP), and βvec. Comparing PU1, PU2, and PU3 to reference substances like urea and p-nitroaniline, a considerably higher NLO activity is estimated. Out of all the compounds, PU3 has the largest NLO response. Such a significant NLO reaction can be attributed to a small HOMO-LUMO gap and high charge transfer. Second-harmonic generation (SHG) and electro-optic Pockel's effect (EOPE) are being explored for dynamic NLO responses. These compounds that are bases of phenyl-urea exhibit a very significant quadratic nonlinear optical response.

Crude oil-water separation with the aid of carbon based materials

Carbon-based materials are commonly utilized in water filtration and purification due to their affordability and environmental friendliness. This study investigates the effectiveness of four different carbon-based materials: activated carbon (AC), graphene oxide (GO), reduced graphene oxide (rGO), and polyethylene (PE) in crude oil–water separation. To test the effectiveness of the separation, light transmission measurements were carried out with the aid of Arduino UNO using a red, green, and blue (RGB) light spectral sensor. The results revealed that the emulsions with AC was the most effective material in the separation, followed by rGO, and GO was the least effective. To explain the mechanism behind the separation performance, the carbon materials have been characterized by x-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR). The effectiveness of AC and rGO in the separation process was directly related to the quantity of surface oxides. The experimental results are perfectly agreed with published Density functional theory (DFT) calculations of HOMO–LUMO gap energies. AC shows the best performance and the smallest gap, which indicates that it requires less energy for electrons transition between the HOMO and LUMO. This phenomenon can be attributed to the affinity towards hydrogen in the hydrocarbon chains in crude oil.

Revisiting Artifacts of Kohn-Sham Density Functionals for Biosimulation.

We revisit the problem of unphysical charge density delocalization/fractionalization induced by the self-interaction error of common approximate Kohn-Sham (KS) density functional theory functionals on simulation of small to medium-sized proteins in a vacuum. Aside from producing unphysical electron densities and total energies, the vanishing of the HOMO-LUMO gap associated with the unphysical charge delocalization leads to an unphysical low-energy spectrum and catastrophic failure of most popular solvers for the KS self-consistent field (SCF) problem. We apply a robust quasi-Newton SCF solver [ Phys. Chem. Chem. Phys. 2024, 26, 6557] to obtain solutions for some of these difficult cases. The anatomy of the charge delocalization is revealed by the natural deformation orbitals obtained from the density matrix difference between the Hartree-Fock and KS solutions; the charge delocalization not only can occur between charged fragments (such as in zwitterionic polypeptides) but also involves neutral fragments. The vanishing-gap phenomenon and troublesome SCF convergence are both attributed to the unphysical KS Fock operator eigenspectra of molecular fragments (e.g., amino acids or their side chains). Analysis of amino acid pairs suggests that the unphysical charge delocalization can be partially ameliorated by the use of some range-separated hybrid functionals but not by semilocal or standard hybrid functionals. Last, we demonstrate that solutions without the unphysical charge delocalization can be located even for semilocal KS functionals highly prone to such defects, but such solutions have non-Aufbau character and are unstable with respect to mixing of the non-overlapping "frontier" orbitals. Caution should be exercised when unexpectedly small (or vanishing) HOMO-LUMO gaps and atypical SCF convergence patterns (e.g., oscillatory) are observed in KS DFT simulations in any context (bio or otherwise).

Ring Structures of Metal Atom Doped C9, C11, and C13 Clusters from Ab Initio Calculations-The Finding of a Gd@C13 Magnetic Superatom Ring.

Pure C9 clusters have a linear chain structure. However, here, we report using ab initio calculations the transformation of a chain into a cyclic ring structure with the capping of Ca, Sr, and Ba atoms. Further calculations on neutral and charged clusters doped with Sc, Y, and La atoms show stabilization of a cation C9 isoelectronic cyclic ring capped with the metal (M) atom, but anion clusters doped with these trivalent atoms form a C10 like MC9 ring, which deforms to a necklace structure. Both the ring structures correspond to electronic shell closing with 20 delocalized valence electrons in a disk jellium model and have a large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. Calculations of IR and Raman spectra show no imaginary frequency, suggesting that the structures are stable. Addition of two C atoms to the ring structure of LaC9 leads to a capped ring structure of the cation LaC11 and an open ring structure of the LaC11 anion. Further addition of two C atoms leads to a La@C13 cation as well as Ca@C13 and Sr@C13 neutral wheel-shaped rings with endohedral doping of the M atom. These novel ring structures have a large HOMO-LUMO gap of more than 4 eV and are magic with electronic shell closing corresponding to 28 delocalized valence electrons in a disk jellium model. There is π aromaticity in this ring satisfying 4n+2 (n = 3) Hückel's rule with 14 valence electrons. Interestingly, when the dopant is a Gd atom, there is a formation of a magnetic superatom ring Gd@C13 + with 7 μB magnetic moments due to seven 4f up-spin states of Gd being fully occupied. Bonding in these novel ring structures is discussed.

Non-covalent interactions-advanced selective trapping of flexible nitrilotriacetamide towards radioactive pertechnetate

Pertechnetate is one of the most prevalent forms of radioactive 99Tc element. Most of traditional extractants have failed in its extraction and separation due to the almost no complexing nature. Recent studies have found that nitrilotriacetamide (NTAamide) derivatives worked well in selectively extracting TcO4−. Herein, the involved extraction process has been visualized by molecular dynamics (MD) simulations, and the mechanism comprehensively examined by further combining density functional theory (DFT) calculations. Study has been extended to other anions MO4− (M = Mn, Re and Pm) of the same group. The competing extraction of TcO4− against SO42−, H2PO4− and F− co-existed in spent nuclear fuels was also delineated. Thermally and structurally stable ternary [HNTAamide+·MO4−·H2O] was recognized for the extracted complex, which well reproduced TcO4−/ReO4− ones from X-ray crystal diffraction and other experimental characterizations. The extraction to MO4− (M = Mn, Tc and Re) is thermodynamically favored, but it is not to PmO4−. Similar overall structures and close interfacial interactions were attained in extracting TcO4− and ReO4−, but the former had more negative reaction energy and narrower HOMO-LUMO gap. This validates the widely-used simulation handling, where ReO4− is used to replace radioactive, toxic and scarce TcO4−. Non-covalent interactions, including hydrogen bonds and weak van der Waals interaction, have been revealed, enabling selective and effective extraction of TcO4− by NTAamide.

Electronic transport properties of tetracene molecular junctions formed with different metallic electrodes

Density functional theory in combination with non-equilibrium Green’s function is employed to study the electron transport properties of tetracene-based molecular junctions formed with silver, gold, copper and platinum electrodes. The physical origin of the IV curves is discussed by analyzing their density of states, molecular projected self-consistent Hamiltonian, transmission spectra, conductance trends and HOMO-LUMO gap at different operating voltages. The results indicate that till a low bias voltage of 1.4 V, the tetracene molecule shows metallic behavior with silver and copper electrodes while semi-metallic and non-metallic nature with gold and platinum electrodes respectively is observed. The zero bias conductance is found to be greatest for Ag followed by Cu and Au with the least in Pt. Furthermore, it is worth mentioning that negative differential resistance feature is observed in molecular junctions with all the electrodes except Pt, with the highest peak-to-valley current ratio of 1.283 found in Ag-Tetracene-Ag molecular junction.

Fullertubes: A 30-Year Story of Prediction, Experimental Validation, and Applications for a Long-Missing Family of Soluble Carbon Molecules.

ConspectusDuring the last 30 years, theoretical scientists imagined segmental families of monolayer carbon tubules with fullerene-based end-caps. These fullertube molecules would possess structural features of both fullerenes (hemispherical end-caps) and tubular belts of single-walled carbon nanotubes (SWCNTs). Yet, their experimental verification remained elusive for decades. It was not until 2020-2023 that segmental families of fullertubes were finally confirmed in the lab. The shocking irony is that these fullertubes were unwittingly coproduced alongside fullerenes (e.g., C60, C70, C84) in both flame and electric arc soot since the 1990s. Yet, nobody knew these "hidden" families of fullertubes were experimentally present in their extracted soot due to their low abundance and the absence of isolation methodology.This eruption of fullertube discoveries in 2020-2023 was brought to fruition by structural data, both DFT and experimental. This "Treasure Trove" of new molecules during this four-year window occurred with only microgram quantities. Typically, milligram levels of purified samples are required for X-ray crystallography and 13C NMR structural analysis. The breakthrough for experimentally verifying the missing fullertubes was an aminopropanol reagent to selectively react with and remove spheroidal carbon (e.g., C60, C70, C84) as hydrophilic derivatives. In contrast, there was suppressed reaction with fullertubes, which remained in organic solvent. It is well established that high symmetry (3-, 5-, and 6-fold) hemispheres for C60-Ih and other fullerenes and metallofullerenes are prerequisite end-caps for fullertubes. For the case of [5,5] C130 fullertubes, this requirement results in only eight 3-, 5-, and 6-fold symmetry structural isomers possible from a total of 39,393 possible isolated pentagon rule (IPR) isomers. From this C130 list of 8 candidate isolated pentagon rule (IPR) high symmetry isomers, surprisingly only one structure matched the DFT polarizability versus chromatographic retention parameter (a new gold standard for isomer identification). The simultaneous emergence of DFT computations of other properties (e.g., total energy, HOMO-LUMO gap, UV-vis) for large carbon molecules provided support for structural determination. Experimental approaches (e.g., mass spectrometry, UV-vis, XPS, Raman, and STEM) provided additional layers of structural elucidation at the microgram level. For the first time, we developed a chemical isolation protocol that would allow the preparation and isolation of soluble pristine fullertubes in the range of C90-C200. To date, applications of SWCNTs for use in nanoscale computer applications requires purities greater than 99.999%. Although this stringent mandate has not yet been demonstrated using SWCNT samples, this high level of purity appears achievable for metallic [5,5] D5d-C120 and semiconductor [10,0] D5h-C120 [10,766] fullertubes. Moreover, commercial production of pristine fullertubes should easily be feasible by the flame method due to its continuous operation and inexpensive feedstock. For application development, theoretical and electrochemical experimental data show that fullertubes exhibit high catalytic activity in oxygen reduction reactions. In the medical sector, pristine fullertube dispersions exhibit antimicrobial effects on Mycobacterium smegmatis and M. abscessus.

Reaction rate of HO2+ 5-methyl-2-furanyl methyl/2-furanyl methyl and its effect on combustion of 2, 5-dimethylfuran/2-methylfuran

A valuable alternative to traditional fuels, bio-oxygenated fuels provide benefits. Oxygenated fuels 2,5-dimethylfuran (DMF) and 2-methylfuran (2MF) perform well. This study used quantum chemical calculations and combustion simulations to evaluate the combustion characteristics of low and medium temperature combustion mechanisms. Conclusions: In the combustion reaction of DMF and 2MF, the H-abstraction reaction occurs mainly at the methyl site. The reaction between macromolecular radicals and HO2 at low and middle temperatures plays a critical role in fuel auto-ignition. Thus, R∙+HO2 ↔ ROOH→R-CHO+H2O and R∙+HO2 → vdw complex → R+3O2 were added to the mechanism. Modified mechanism improves temperature prediction accuracy. The HOMO-LUMO gap is narrowed by the methyl group, which is closely related to the reaction sites and the molecular structure. After H-abstraction, the methyl site is the most likely to react, followed by the C3 and C5 sites.

Structural evolution and electronic properties of anionic plutonium-doped oxygen clusters

Plutonium oxides are important in actinide chemistry and nuclear industry activities, and the demand and interest in enriching knowledge of plutonium chemistry is growing increasingly significant. However, unlike uranium oxide clusters, few studies related to the geometry and bonding properties of anionic plutonium oxide clusters have been reported. Here we explored the geometries, photoelectron spectra, and electronic properties of anionic plutonium oxide clusters by means of unbiased structural searches coupled with density-functional theory (DFT). The results show that the PuO6− cluster with a high D2h symmetry formed by a linear O-Pu-O plutonyl unit with two O2 units exhibits excellent stability. In addition, the HOMO–LUMO gap value of PuO6− cluster are 4.35 eV and 3.41 eV for the α- and β-orbitals, respectively, as well as the vertical detachment energy (VDE) of 4.20 eV. In the analysis of molecular orbitals and adaptive natural density partitioning in oxygen-rich systems, the σ bonds between plutonium atom and oxygen ligands, primarily from the Pu-5f and O-2p orbitals, are responsible for the goodish stability of PuO6− cluster. We hope that the current work can enrich the geometrical configuration of plutonium oxide oxygen clusters and provide reference information for the subsequent research work.

A Configurationally Stable Helical Indenofluorene.

We report the synthesis and study of the optoelectronic, magnetic, and chiroptical properties of a helically chiral diradicaloid based on dibenzoindeno[2,1-c]fluorene. The molecule shows a small HOMO-LUMO gap and a moderate singlet-triplet gap, which agrees with the results of DFT calculations. The helical structure of the compound, confirmed by X-ray diffraction, is configurationally stable, which allows the isolation of both enantiomers and the evaluation of the chiroptical properties (ECD).

Impact of the chemical insertion of the dimethylamino group on the electronic and optical properties of the 4-(methoxyphenyl acetonitrile) monomer (MPA): a DFT theoretical investigation.

Density functional theory (DFT) calculations on the ground and the first excited state are performed on the modified and unmodified 4-(methoxyphenyl acetonitrile) monomer (referred to as MPA). The modified monomer named MFA is obtained by Knoevenagel condensation of MPA with dimethylformamide dimethyl acetal (DMF-DMA). DFT computations show that the chemical grafting of the dimethylamino group onto the MPA unit induces a great change in the geometric, electronic, and optical properties. Going from MPA to MFA monomer, a great change in the frontier orbitals of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the ground and the first excited state is observed. Consequently, a reduction in the energy gap HOMO-LUMO and an enhancement in the absorption and emission properties are observed under the chemical modification. The observed modifications in the electronics and optical properties are the result of the charge transfer appearing between the cyano (C≡N) acceptor group and the dimethylamino (DMF-DMA)-grafted group donor ring. Quantum chemical calculations were performed in the ground and the first excited state using the density functional theory (DFT), and it extends the time-dependent density functional theory (TD-DFT), implemented in the Gaussian 09 software package. The ground state is obtained by optimization of the studied molecular geometries by employing the DFT/M062X/6-31G(d,p) level of theory. The first excited state is obtained by re-optimization of the ground state geometries using the TD-DFT/M062X/6-31G(d,p) level of theory. The contour plots of the frontier orbitals and the molecular electrostatic potential (MEP) maps are obtained from the ground and the first excited state, optimized geometries, and drawn using Gaussview software.

Adsorption behavior of HFCO and COF2 gasses on pristine, Al-doped, and N-doped (8, 0) single-wall carbon nanotubes and pristine aluminum nitride nanotube: A first-principles study

The detection of organic pollutants in the environment is crucial due to their significant impact on human health. Formyl fluoride (HFCO) and carbonyl fluoride (COF2) are toxic gasses that contribute to stratospheric ozone depletion. To explore a potential sensor material for these compounds, the adsorption properties of HFCO and COF2 on pristine (8, 0) single-walled carbon nanotubes (SWCNTs), aluminum-doped SWCNTs (Al-SWCNTs), nitrogen-doped SWCNTs (N-SWCNTs), and aluminum nitride nanotube (AlNNTs) were investigated using density functional theory (DFT) calculations. Obtained structural and electronic results reveal no significant after HFCO and COF2 adsorption on pristine SWCNT. However, the conductivity and polarizability of Al- SWCNT increases throw HFCO and COF2 adsorption. It was shown that this adsorption strongly depends on molecular orientation toward SWCNT. Structural and electronic findings show that studied molecules undergoes a physical adsorption to N- SWCNT. However, AlNNT was also found to show significant changes in structural and electronic properties after HFCO and COF2 adsorption. This adsorption leads to a significant (nearly 45%) reduction in the HOMO-LUMO gap of AlNNTs. Therefore, it is proposed from this study that Al-SWCNTs and AlNNTs are promising candidates for HFCO and COF2 gas sensors. Moreover, AlNNTs exhibit intrinsic detection capabilities without structural manipulation via doping which makes AlNNTs particularly attractive for sensor applications. Moreover, the capability of AlNNT without manipulating makes this nanotube a good and easy made candidate for these compounds adsorption.

Zero-Bias Anti-Ohmic Behaviour in Diradicaloid Molecular Wires.

Open-shell materials bearing multiple spin centres provide a key route to efficient charge transport in single-molecule electronic devices. They have narrow energy gaps, and their molecular orbitals align closely to the Fermi level of the metallic electrodes, thus allowing efficient electronic transport and higher conductance. Maintaining and stabilising multiple open-shell states-especially in contact with metallic electrodes-is however very challenging, generally requiring a continuous chemical or electrochemical potential to avoid self-immolation of the open-shell character. To overcome this issue, we designed, synthesised, and measured the conductance of a series of bis(indeno) fused acenes, where stability is imparted by a close-shell quinoidal conformation in resonance with the diradical electronic configuration. We show here that these compounds have anti-ohmic behaviour, with conductance increasing with increasing molecular length, at an unprecedented rate and across the entire bias window ( ). Density Functional Theory (DFT) calculations support our findings, showing the rapidly narrowing HOMO-LUMO gap, unique to these diradicaloid structures, is responsible for the observed behaviour. Our results provide a framework for achieving efficient transport in neutral compounds and demonstrate the promise that diradicaloid materials have in single-molecule electronics, owing to their great stability and unique electronic structure.

Quamtum Mechanical Study on Structural and Electronic Properties of Tert-Butyl Based Bridged Dithiophene Oxide Derivatives

Computational modeling is vital to designing and creating organic semiconductors used in solar cells, organic field-effect transistors, and other areas. This work studied the structural and electronic features of a group of substituted tert-butyl bridged dithiophene oxide derivatives using Density Functional Theory (DFT) calculations. Geometry improvements were carried out using the B3LYP hybrid functional and the 6-31G(d,p) basis set in Gaussian 09. Molecular shapes, bond lengths, bond angles, and dihedral angles were studied to find out how substitution patterns change the packing and conformation of molecules. Energy levels, distribution, and makeup of frontier molecular orbitals were found. This calculation also included finding other electronic qualities, such as electronic charges, dipole moments, and polarizabilities. Findings show that tert-butyl substitution makes the molecular backbone stiffer and limits its ability to twist compared to similar molecules that have not been replaced. The chemical geometry stays mostly the same when electron-withdrawing or electron-donating substituents are added to the tert- butyl groups. Nevertheless, the strength and location of substituents have a significant impact on frontier orbital energies. The HOMO-LUMO gap grew significantly when the nitro or cyano groups firmly pulled electrons away from derivatives. For successful charge transport, electron density plots show that the HOMO and LUMO are mainly located on the thiophene and substituent moieties, respectively. Molecular dipole moments are also strongly affected by the electronic features of substituents. This research shows how to change the optoelectronic properties of tert-butyl-based dithiophene oxide derivatives and how their structure-property relationships can be improved. The results help makes new organic semiconductors that work better in various electronic and optoelectronic uses.