HOMO-LUMO Gap Research Articles

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).

Hydrogen storage on MgO supported TiMgn (n = 2–6) clusters: A first principle investigation

The current study explores the potential of MgO-supported finite-sized TiMgn (n = 2–6) nanoclusters as hydrogen storage materials, employing density functional theory with a spin-polarized generalized gradient approximation (GGA). These systems' structural stability and electronic characteristics reveal that supported clusters offer superior hydrogen storage capabilities compared to their unassisted counterparts. Various parameters, including cluster-adsorption energy (Eads), hydrogen-adsorption energy in supported clusters (Eads-H), HOMO-LUMO gap, vertical ionization potential (VIP), vertical electron affinity (VEA), chemical potential (μ), and chemical hardness (ɳ) are computed. Substrate support notably enhances the thermodynamic stability and chemical reactivity of the TiMg5 cluster when contrasted with the bare TiMg5 cluster. Furthermore, a remarkable increase in the gravimetric hydrogen storage density, from 1.63 wt% for bare Mg5 clusters to 3.45 wt% for bare TiMg5 clusters, reaching 5.62 wt% in the supported TiMg5 cluster system is observed. These findings indicate the substrate-supported TiMg5 cluster as a promising candidate for hydrogen storage applications.

Enhancing visible light photocatalytic activity of holmium doped g-C3N4 and DFT theoretical insights.

In the search of novel photocatalysts to increase the effect of visible light in photocatalysis, g-C3N4 (CN) has become a shining star. Rare earth metals have been used as dopant material to reinforce the photocatalytic activity of CN due to their unique electron configuration recently. In this present study, the pure and different amounts of Ho-doped g-C3N4 (HoCN) photocatalysts were successfully synthesized using urea as a precursor by the one-pot method. Morphological, structural, optical, and vibrational properties of the synthesized photocatalysts were characterized by SEM, EDX, XRD, TGA, XPS, FTIR, PL, TRPL, Raman, DRS, and BET analyses. In addition, theoretical calculations using density functional theory (DFT) were meticulously carried out to delve the changes in the structural and electronic structure of CN with holmium doping. According to calculations, the chemical potential, electrophilicity, and chemical softness are higher for HoCN, while HOMO-LUMO gap, dipole moment, and the chemical hardness are lower for the pure one. Thus, holmium doping becomes desirable with low chemical hardness which indicates more effectivity and smaller HOMO-LUMO gap designate high chemical reactivity. To determine the photocatalytic efficiency of the pure and doped CN photocatalysts, the degradation of methylene blue (MB) was monitored under visible light. The results indicate that holmium doping has improved the photocatalytic activities of CN samples. Most strikingly, this improvement is noticeable for the 0.2mmol doped CN sample that showed two times better photocatalytic activity than the pure one.

Accurate and efficient prediction of optical gaps in silicon and germanium nanoparticles using a high-local-exchange density functional

We investigated the HOMO-LUMO gaps and the optical gaps of Si and Ge nanoparticles (NPs) with various terminations and sizes using different functionals (HLE16, B3LYP, HSE-HJS) and basis sets (CRENBL, def2-SVP, def2-TZVP). The high-local-exchange functional HLE16, without Hartree–Fock exchange, effectively reproduces optical gaps using HOMO−LUMO gaps, offering a cost-effective alternative to hybrid functionals and TDDFT in nanoscale systems. Size (quantum confinement effects) and termination ligands (surface effects) significantly impact energy gaps: nonpolar CH3 had minimal effects, while polar ligands reduced gaps notably. Finally, ECP basis sets like CRENBL are better suited for NP electronic structures than all-electron basis sets.

Ring and Linear Structures of CdTe Clusters

We report the results of an ab initio study of the linear and ring structures of cadmium telluride clusters [CdTe]n (CdnTen) n ≤ 10 within the generalized gradient approximation (GGA) and Purdue–Burke–Ernzerhof (PBE) parameterization with Hubbard corrections (GGA+U). We optimized the linear and ring isomers for each size to obtain the lowest-energy structures and to understand their growth behavior. The cases of n < 8 for ring-type structures and n = 6 and 9 for linear-type structures were found to be the most favorable. All observed clusters with a linear structure were found to have a small highest-occupied–lowest-unoccupied molecular orbital (HOMO–LUMO) gap. The CdTe clusters with ring structure showed larger values of the HOMO–LUMO gaps than the band gap value for the bulk crystal. Structural and electronic properties like bond length, the HOMO–LUMO gap, binding energy, and electronegativity were analyzed.

A Triply Linked Copper(III) Dicarbacorrole Dimer.

A triply linked dicarbacorrole dimer (7) was synthesized from a new meso-meso singly linked dicarbacorrole dimer precursor (6) via an oxidative fusion reaction by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in the presence of trifluoromethanesulfonic acid (TfOH). Single crystal X-ray structure of 7 adopts a flat conformation with a length as ca. 15.946 Å and a width as 6.903 Å, which can be regarded as a short carbaporphyrinoid tape. Two coordinated Cu ions keeps the +3 oxidation state in 7, as confirmed by NMR spectroscopy, single crystal X-ray diffraction and X-ray photoelectron spectroscopy (XPS). This is in sharp contrast to the Osuka's triply linked tetrapyrrolic corrole dimers, where the inner 3NH form is not stable and thus can only act as a divalent ligand. Due to the non-aromatic nature of dicarbacorrole macrocycle, the largely decreased HOMO-LUMO gap and red-shifted absorption of 7 are best ascribed to the strong electronic interaction between two dipyrromethene-type chromophores. To our knowledge, this is the first fully fused carbaporphyrinoid dimer with β-β, meso-meso, β-β triply linkages prepared to date.

Overcrowded 14,14'-Bidibenzo[a,j]anthracenes: Challenges in Syntheses and Atypical Property of Lacking Symmetry-Breaking Charge Transfer (SBCT).

14,14'-Bidibenzo[a,j]anthracenes (BDBAs) were prepared by iridium-catalyzed annulation of 5,5'-biterphenylene with alkynes. The molecular geometries of overcrowded BDBAs were verified by X-ray crystallography. The two dibenzo[a,j]anthryl moieties are connected through the sterically hindered 14 positions, resulting in highly distorted molecular halves. The conformation with a small twist angle between two molecular halves can minimize steric conflicts between the substituents at 1 and 13 positions and the carbon atoms of the central axis, as well as steric clashes between those substituents. One such example is octafluoro-substituted BDBA, where the interplanar angle between two anthryl moieties is approximately 31° (currently the lowest reported value, cf. 81° in 9,9'-bianthracene). The intramolecular interactions and electronic couplings between two molecular halves resulted in upfield 1H NMR signals, redshifted absorption and emission bands, and a reduced HOMO-LUMO gap. Photodynamic investigations on BDBAs indicated that the formation of the conventional symmetry-breaking charge transfer (SBCT) state was suspended by restricted rocking around the central C-C bond. Such a mechanism associated with this highly constrained conformation was examined for the first time.

Nonlinear optical properties of KnCl (n = 2–7) superalkali clusters

The lowest energy structures along with the low lying isomer, stabilities, electronic properties, optical properties and nonlinear optical responses of KnCl (n = 2–7) clusters were studied within the density functional theory. The second order energy difference, dissociation energy and GH-L (HOMO–LUMO gap) point out that KnCl (n = 3, 5, 7) clusters are more stable. The calculated adiabatic ionization energies (AIE) for the KnCl (n = 2–6) clusters are in agreement with the measured ionization energies. The optical properties, namely optical electronegativity and refractive index, depends on the GH-L energy values. The K atom capped planar rhombus geometry of the K4Cl causes the noticeable vibrational frequency shift compared to the rest of IR spectra of the clusters. The first static hyperpolarizability (β o) values are in the range of 2.33 × 103 –2.87 × 104 au and the second static hyperpolarizability varies between 5.74 × 106 au and 38.9 × 106 au for the cluster. The nonlinear optical response is due to the superalkali nature of KnCl (n = 2–7) clusters. From computed β vec values, the hyperpolarizability has projection on the dipole moment vector for the superalkalis except the K2Cl and K5Cl. The absorption spectra point out that KnCl (n = 6–7) clusters can be suitable as a NLO material since they have transparency in the deep UV region (λ< 300 nm).

Theoretical study on the structure, spectroscopic, and current–voltage behavior of 11-Cis and Trans retinal isomers in rhodopsin

In this study, the electronic transport properties of 11-Cis and Trans retinal, components of rhodopsin, were investigated as optical molecular switches using the nonequilibrium Green’s function (NEGF) formalism combined with first-principles density functional theory (DFT). These isomers, which can be reversibly converted into each other, were examined in detail. The structural and spectroscopic properties, including infrared (IR), Raman, nuclear magnetic resonance (NMR), and ultraviolet (UV) spectra, were analyzed using the hybrid B3LYP/6–311 + + G** level of theory. Complete vibrational assignments were performed for both forms utilizing the scaled quantum mechanical force field (SQMFF) methodology. To evaluate the conductivity of these molecules, we utilized current–voltage (I-V) characteristics, transmission spectra, molecular projected self-consistent Hamiltonian (MPSH), HOMO–LUMO gap, and second-order interaction energies (E2). The trendline extrapolation of the current–voltage plots confirmed our findings. We investigated the effect of different electrodes (Ag, Au, Pt) and various connection sites (hollow, top, bridge) on conductivity. The Ag electrode with the hollow site exhibited the highest efficiency. Our results indicate that the Cis form has higher conductivity than the Trans form.

Electronic Structure of Metallophlorins: Lessons from Iridium and Gold Phlorin Derivatives.

Phlorins have long remained underexplored relative to their fully conjugated counterparts, such as porphyrins, hydroporphyrins, and corroles. Herein, we have attempted to bridge that knowledge gap with a scalar-relativistic density functional theory (DFT) study of unsubstituted iridium and gold phlorin derivatives and a multitechnique experimental study of iridium-bispyridine and gold complexes of 5,5-dimethyl-10,15,20-tris(pentafluorophenyl)phlorin. Theory and experiments concur that the phlorin derivatives exhibit substantially smaller HOMO-LUMO gaps, as reflected in a variety of observable properties. Thus, the experimentally studied Ir and Au complexes absorb strongly in the near-infrared (NIR), with absorption maxima at 806 and 770 nm, respectively. The two complexes are also weakly phosphorescent with emission maxima at 950 and 967 nm, respectively. They were also found to photosensitize singlet oxygen formation, with quantum yields of 40 and 28%, respectively. The near-infrared (NIR) absorption and emission are consonants with smaller electrochemical HOMO-LUMO gaps of ∼1.6 V, compared to values of ∼2.1 V, for electronically innocent porphyrins and corroles. Interestingly, both the first oxidation and reduction potentials of the Ir complex are some 600 mV shifted to more negative potentials relative to those of the Au complex, indicating an exceptionally electron-rich macrocycle in the case of the Ir complex.

'Passivated Precursor' Approach to All-Alkynyl-Protected Gold Nanoclusters and Total Structure Determination of Au130.

A 'passivated precursor' approach is developed for the efficient synthesis and isolation of all-alkynyl-protected gold nanoclusters. Direct reduction of dpa-passivated precursor Au-dpa (Hdpa = 2,2'-dipyridylamine) in one-pot under ambient conditions gives a series of clusters including Au22(C≡CR)18 (R = -C6H4-2-F), Au36(C≡CR)24, Au44(C≡CR)28, Au130(C≡CR)50, and Au144(C≡CR)60. These clusters can be well separated via column chromatography. The overall isolation yield of this series of clusters is 40% (based on gold), which is much improved in comparison with previous approaches. It is notable that the molecular structure of the giant cluster Au130(C≡CR)50 is revealed, which presents important information for understanding the structure of the mysterious Au130 nanoclusters. Theoretical calculations indicated Au130(C≡CR)50 has a smaller HOMO-LUMO gap than Au130(S-C6H4-4-CH3)50. This facile and reliable synthetic approach will greatly accelerate further studies on all-alkynyl-protected gold nanoclusters.

Silyliumylidene Ion Stabilized by Two σ-Donating Ni(0)- and Pd(0)-Fragments.

A silyliumylidene ion 2 stabilized by two σ-donating Ni(0)- and Pd(0)-fragments was successfully synthesized. Due to the σ-donation of M→Si interactions, 2 presents a pyramidalized cationic silicon center with a localized lone pair. The additional coordination of basic Pd(0) fragment to the mono-Ni(0)-stabilized silyliumylidene 1 results in a higher HOMO level and an unchanged HOMO-LUMO gap and thus, 2 remains highly reactive. Interestingly, the coordination mode at the Si center is closely related to the nature of M-ligands. Indeed, the donor/donor-stabilized silyliumylidene ion 2 has been transformed into a donor/acceptor-stabilized ion 13, featuring a trigonal planar Si center with a vacant orbital, just via a ligand exchange reaction from PCy3/NHC toward PMe3.

Examination of structural and spectrophotometric optical characteristics of nano-like flower quinolinyl carbonyl pyrazole-1-carbodithioate films: a new trend for optoelectronic applications

The current investigation entailed the synthesis of benzyl 5-amino-4-[(1-ethyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-3-yl)carbonyl]-1H-pyrazole-1-carbodithioate (referred as BAEHQP, compound 2) from 6-ethyl-4,5-dioxo-5,6-dihydro-4H-pyrano[3,2-c]quinoline-3-carbonitrile (compound 1), followed by its characterization in nanocrystalline thin films produced through thermal evaporation in a high vacuum. Computational and experimental methodologies were employed for this purpose. Density functional theory (DFT) calculations using the B3LYP/6-311++G(d,p) basis set were utilized to predict the HOMO-LUMO gap and evaluate the global reactivity descriptors, elucidating the chemical hardness, kinetic stability, and electron-donating capabilities. X-ray diffraction (XRD) analysis verified the presence of a polycrystalline structure in the BAEHQP powder and indicated an amorphous nature in the thin film. Utilizing the Williamson-Hall formula, the mean crystallite size and microstrain were determined to be 63.36 nm and 0.00667, respectively. Scanning electron microscopy corroborated the nanoflower-like structure, and particle size analysis was conducted to determine the size distribution. The optical properties, encompassing both linear and nonlinear aspects, of BAEHQP thin film were investigated using spectrophotometric methods, delineating band transitions and identifying a fundamental direct energy gap of 2.2 eV. The distinct attributes of thin-film absorption and dispersion were outlined, and the unanticipated findings hold potential implications for advancing the industrialization of photodiode device manufacturing.

Theoretical design of alkaline earthides M+(36 adz) Be− (M+ = V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) with excellent nonlinear optical response and ultraviolet transparency

A novel series of alkaline earthides containing eight complexes based upon 36adz complexant are designed by placing carefully transition metals (V–Zn) on inner side and alkaline earth metal outer side of the complexant i.e., M+(36adz) Be− (M+ = V, Cr, Mn, Fe, Co, Ni, Cu and Zn). All the designed compounds are electronically and thermodynamically stable as evaluated by their interaction energy and vertical ionization potential respectively. Moreover, the true nature of alkaline earthides is verified through NBOs and FMO study, showing negative charge and excess electrons on alkaline earth metal respectively. Furthermore, true alkaline earthides characteristics are evaluated graphically by spectra of partial density state (PDOS). The energy gap (HOMO -LUMO gap) is very small (ranging 2.95 eV–1.89 eV), when it is compared with pure cage 36adz HOMO-LUMO gap i.e., 8.50 eV. All the complexes show a very small value of transition energy ranging from 1.68eV to 0.89eV. Also, these possess higher hyper polarizability values up to 2.8 x 105au (for Co+(36adz) Be−). Furthermore, an increase in hyper polarizability was observed by applying external electric field on complexes. The remarkable increase of 100fold in hyper polarizability of Zn+(36adz) Be− complex is determined after application of external electric field i.e., from 1.7 x 104 au to 1.7 x 106 au when complex is subjected to external electric field of 0.001 au strength. So, when external electric field is applied on complexes it enhances the charge transfer, polarizability and hyper polarizability of complexes and proves to be effective for designing of true alkaline earthides with remarkable NLO response.

Synthesis, crystal structure, in vitro anticholinesterase activity, molecular docking and DFT investigation of three 1,10-phenanthroline-tin(IV) complexes

This work describes the synthesis, the crystal structure and the properties of three tin complexes derivatives of 1,10-phenanthroline, namely C24H19N3SnCl2 (C1), C24H20N4SnCl2 (C2) and C27H22N4SnCl2 (C3). Their structures were elucidated by X-ray diffraction, IR and NMR (1H &13C). The in vitro anticholinesterase activity was investigated and compared to docking findings. The obtained results showed that the C2 complex presents the closest IC50 value (10.99±0.34 μM) to that of galantamine (4.14±0.07 μM) and corroborated by the docking results, where C2 and C1 showed a score of 54.08, 51.32 for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activity, respectively. The optimized structures obtained by density functional theory (DFT) gave comparable geometrical parameters around the tin(IV) cation of hexacoordination environment. The computed HOMO-LUMO gaps are large predicting stable compounds. The natural population analysis attributes negative charges of chlorine, carbon and nitrogen atoms directly bound to the tin(IV) cation. However, the natural charges of tin(IV) of +1.63 in both C1 and C2 compounds are lower than +1.74 calculated for C3, suggesting different electron transfers. The FMOs localizations and Fukui functions predict that C1 and C2 behave differently from C3 with regard to the reactivity towards protein targets, in agreement with the experimental data and the molecular docking results.

Kinetically stabilized 1,3-diarylisobenzofurans and the possibility of preparing large, persistent isoacenofurans with unusually small HOMO-LUMO gaps.

DFT calculations demonstrate that an isoacenofuran of any size possesses a smaller HOMO-LUMO gap than the corresponding acene bearing an isoelectronic π-system (i.e., the same total number of rings). Isoacenofurans show limited stability due in part to the highly reactive 1,3-carbons of the furan ring. Both 1,3-dimesitylisobenzofuran and 1,3-di(2',4',6'-triethylphenyl)isobenzofuran, each bearing sterically congesting ortho-alkyl groups on their phenyl substituents, have been synthesized and shown to adopt non-planar conformations with the ortho-alkyl groups located above and below the most reactive 1,3-carbons of the furan ring. These bulky substituents provide a strong measure of kinetic stabilization. Thus, 1,3-dimesitylisobenzofuran and 1,3-di(2',4',6'-triethylphenyl)isobenzofuran are significantly less reactive than 1,3-diphenylisobenzofuran toward the strong dienophiles DMAD and acrylonitrile. The insights gained here suggest that the synthesis of large, persistent, kinetically stabilized isoacenofurans with unusually small HOMO-LUMO gaps is achievable. As such, these molecules deserve increased attention as potential p-type organic semiconductors.

Triple crossed 3 C26 cyclic cumulene catenane

Cumulenes are valuable precursors to an entire series of more complex organic derivatives. Cyclic cumulenes present a special case, since they possess an increased potential to possess a high order of symmetry. The stability of the cumulene molecule can be brought forth through the construction of crossed clusters. In this case, molecular modeling tools were employed in order to provide insights into the construction and stability of 3 C26 triple crossed C26 cyclic cumulene cluster. The study revealed that is a very little change in the total energy per atom (or per electron) of triple crossed 3 C26 when compared with C26 (0.00002 Hartree/e, which is less than 0.01 ‰). Other important parameters, such as the HOMO-LUMO gap and the angles between the planes of the molecular rings, suggest its kinship with fullerenes and the regular tetrahedron. Furthermore, in order to proof the suitability of the approach and of its results a symmetry constrained optimization study was conducted using Z-matrix internal coordinates with Gaussian software. At DFT BLYP 6-311 G* theory level a symmetry constrained optimization of the 3 C26 cluster converged, which suggests the possibility of obtaining this cluster by synthetic means.

Multifunctional in vitro, in silico and DFT analyses on antimicrobial BagremycinA biosynthesized by Micromonospora chokoriensis CR3 from Hieracium canadense

Among the actinomycetes in the rare genera, Micromonospora is of great interest since it has been shown to produce novel therapeutic compounds. Particular emphasis is now on its isolation from plants since its population from soil has been extensively explored. The strain CR3 was isolated as an endophyte from the roots of Hieracium canadense, and it was identified as Micromonospora chokoriensis through 16S gene sequencing and phylogenetic analysis. The in-vitro analysis of its extract revealed it to be active against the clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Candida tropicalis (15 mm). No bioactivity was observed against Gram-negative bacteria, Escherichia coli ATCC 25922, and Klebsiella pneumoniae ATCC 706003. The Micromonospora chokoriensis CR3 extract was also analyzed through the HPLC-DAD-UV–VIS resident database, and it gave a maximum match factor of 997.334 with the specialized metabolite BagremycinA (BagA). The in-silico analysis indicated that BagA strongly interacted with the active site residues of the sterol 14-α demethylase and thymidylate kinase enzymes, with the lowest binding energies of − 9.7 and − 8.3 kcal/mol, respectively. Furthermore, the normal mode analysis indicated that the interaction between these proteins and BagA was stable. The DFT quantum chemical properties depicted BagA to be reasonably reactive with a HOMO-LUMO gap of (ΔE) of 4.390 eV. BagA also passed the drug-likeness test with a synthetic accessibility score of 2.06, whereas Protox-II classified it as a class V toxicity compound with high LD50 of 2644 mg/kg. The current study reports an endophytic actinomycete, M. chokoriensis, associated with H. canadense producing the bioactive metabolite BagA with promising antimicrobial activity, which can be further modified and developed into a safe antimicrobial drug.

Nanoscale Dodecahedral and Fullerene-Type Organoboroxine and Borazine Cages from Planar Building Units.

Boroxine- and borazine-cage analogs to C20, C60, and C70 were calculated and compared in terms of structure, strain indicators, and physical properties relevant to nanoscale applications. The results show C60 and C70 type cages are less strained than the smaller congener, primarily due to minimized bending in the B-arylene-B segments. The smallest cage calculated has a diameter of 2.4 nm, which increases up to 4.9 nm by either variation of the polyhedron (C20 < C60 < C70-type cage) or organic spacer elongation between boron centers. All calculated cages are porous (apertures ranging from 0.6 to 1.9 nm). Molecular electrostatic potential and Hirshfeld population analysis revealed both nucleophilic and electrophilic sites in the interior and exterior cage surfaces. HOMO-LUMO gaps range from 3.98 to 4.89 eV and 5.10-5.18 eV for the boroxine- and borazine-cages, respectively. Our findings provide insights into the design and properties of highly porous boroxine and borazine cages for nanoscience.

External Electric Field Control of Exciton Motion in Porphyrin-Based Metal Organic Frameworks.

Porphyrins are excellent light-harvesting complexes. Presently they are unsuitable for photovoltaic applications, as their excellent light absorbance is compensated to a large extent by their poor transport properties, where most excitons are lost by recombination. Arranging porphyrins in regular, strongly bound, lattices of surface-anchored metal-organic frameworks (PP-SURMOFs) may facilitate charge carrier dissociation, but does not significantly enhance the conductive properties. In most cases, photogenerated excitons traverse undirected, Brownian motion through a hopping process, resulting in a substantial diffusion length to reach electrodes, leading to significant exciton loss through recombination. Here, we propose to guide exciton diffusion indirectly by an external electric field. We show that electric fields, even as strong as 1 V nm-1, do not affect the HOMO-LUMO gap of the porphyrins. However, fields of 0.1 V nm-1 and even less demonstrate a notable Stark effect, with slight band gap reductions, for some PP-SURMOFs. When applied as an electric field gradient, for instance, via the substrate, it creates a unidirectional hopping pathway for the excitons. Consequently, we expect a significant reduction of exciton diffusion length leading to increased utilization of photogenerated excitons as they reach the electrodes. This strategy holds promise for integrating photoactive molecules in photovoltaic and photocatalytic applications.