High HOMO-LUMO Gap Research Articles

Structure, electronic and optical properties of chalcopyrite-type semiconducting materials XGaY2 (X = Cu, Ag, Au; Y = S, Se, Te) for solar cell applications: A DFT study

Due to a large scale demand of optoelectronics and photovoltaics devices, the study of chalcopyrite-type semiconducting materials has emerged as one of the significant domains for research. In this report, structure and physico-chemical properties of XGaY2 (X = Cu, Ag, Au; Y= S, Se, Te) are examined in terms of Density Functional Theory technique. The energy differences between the Highest Occupied Molecular orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) of these chalcopyrite-type materials range from 2.363 eV to 3.134 eV. The compound AuGaS2 with the maximum energy gap is observed as the most stable system. Chalcopyrite materials with low HOMO-LUMO gap have the highest refractive indices and dielectric constants. Similarly, materials having high HOMO-LUMO gap display a high optical electronegativity, vibrational frequency, infrared and Raman spectra. It is observed that HOMO-LUMO gap, optical electronegativity, vibrational frequency, infrared and Raman spectra gradually decrease from sulphur to selenium to tellurium.

Novel Fe2+ responsive nanofibrous membrane for corrosion detection and adsorption

Quick detection of iron corrosion and scrap metal adsorption, two major threats to human lives and social prosperity, have aroused rising research attention. In this study, an in-situ Fe 2+ indication and adsorption nanofibrous membrane were prepared taking advantage of electrospun technology. Thanks to the synergistic effect of physical and chemical adsorption, a high Fe 2+ adsorption capacity of 218.11 mg/g was achieved, which was verified by scanning electron microscope and simulation results. A distinct color change from white to red, with a board detection range from 1 to 1000 ppm, could be detected within 10 s. Relatively high HOMO-LUMO gap and partially ligand-centered charge transfer (LC), led to the color change of Phen-Fe 2+ fibrous membrane. The binding energy between Fe 2+ and phenanthroline is strong, making it reliable to iron corrosion detection and adsorption in a real-life situation. • PSA-Phen nanofibers were quickly responsive to Fe 2+ . • The Fe 2+ adsorption capacity in water can reach up to 218.11 mg/g. • The already adsorbed paper could be recycled by in-situ oxidation reaction.

Site specific interactions of amino acids with (ZnO)12 cluster: Density functional approach

The Stability and electronic properties of bio-hybrid molecules are investigated in the framework of the first-principles density functional theory. The site-specific interactions between (ZnO)12 nano-cluster and arginine/aspartic acid are investigated. There are partially ionic and covalent bonds between the interacting atoms, higher binding energy 8.86 eV is observed at –COOH site of arginine, and 7.60 eV at –CN site of aspartic acid during the interaction with a nano-cluster. Higher HOMO-LUMO gap 4.3 eV is found in arginine, and smaller 2.6 eV in a cluster, it becomes zero with –COOH site of arginine, and 0.8 eV at –CN site of aspartic acid during the formation of bio-hybrids, i.e. highly stable amino acids arg/asp-nano-cluster (ZnO)12 bio-hybrids are formed with small forbidden energy-gap. This study will support in the formation of drugs which will improve the response in wound healing, immune functioning in burn injuries, and in the treatment of bone dysfunction. Highlights The binding energy is higher in a bio-hybrid at –COOH site of Arg, and –CN site of Asp. HOMO-LUMO gap is higher in a pristine Arg (4.3 eV), smaller in a cluster (2.6 eV), zero gap in a bio-hybrid with –COOH site of Arg, smaller 0.8 eV at –CN site of Asp. Higher binding energy is found with the small forbidden energy-gap of bio-hybrid molecules. This study will support in the formation of drugs which will improve the response in wound healing, immune functioning in burn injuries, and in the treatment of bone dysfunction. Communicated by Ramaswamy H. Sarma

Computational prediction of small molecules with predicted binding to FGFR3 and testing biological effects in bone cells

Activating anabolic receptor-mediated signaling is essential for stimulating new bone formation and for promoting bone healing in humans. Fibroblast growth factor receptor (FGFR) 3 is reported to be an important positive regulator of osteogenesis. Presently, recombinant proteins are used to stimulate FGFR3 function but have limitations for therapy due to expense and stability. Therefore, there is a need for identification of novel small molecules binding to FGFR3 that promote biological function. In silico molecular docking and high-throughput virtual screening on zinc database identified seven compounds predicted to bind to an active site within the βCʹ-βE loop, specific to FGFR3. All seven compounds fall within an acceptable range of ADME/T properties. Four compounds showed a 30–65% oral absorption rate. Density functional theory analysis revealed a high HOMO-LUMO gap, reflecting high molecular stability for compounds 14977614 and 13509082. Five compounds exhibited mutagenicity, while the other three compounds presented irritability. Computational mutagenesis predicted that mutating G322 affected compound binding to FGFR3. Molecular dynamics simulation revealed compound 14977614 is stable in binding to FGFR3. Furthermore, compound 14977614, with an oral absorption rate of 60% and high molecular stability, produced significant increases in both proliferation and differentiation of bone marrow stromal cells in vitro. Anti-FGFR3 treatment completely blocked the stimulatory effect of 14977614 on BMSC proliferation. Ex vivo treatment of mouse calvaria in organ culture for seven days with 14977614 increased mineralization and expression levels of bone formation markers. In conclusion, computational analyses identified seven compounds that bind to the FGFR3, and in vitro studies showed that compound 14977614 exerts significant biological effects on osteogenic cells.

Fighting cancer with translation inhibitors: a quantum mechanics view on the complex between the antitumor marine alkaloid agelastatin A and the yeast 80S ribosome

The alkaloid agelastatin A (AGA) has raised great interest for its potent antitumor activity and intriguing molecular structure. This led to multifarious total syntheses and the antitumor activity was related to eukaryotic translation inhibition, unraveling the structure of the complex with the 80S yeast ribosome at atomic level. What remained unanswered is the relative weight of the various interactions, a hierarchy of great interest in planning improved antitumor agents in the AGA family. This has been investigated here along QM-MM in explicit water. What emerged was a high and constant HOMO-LUMO gap, speaking for a robust AGA-ribosome complex also in solution, within which AGA’s relaxed twisting ability showed up markedly. It became also clear that AGA’s ring A, despite its formal representation, has no pyrrole properties. Br-π and π-π stacking interactions and H-bonds with surrounding nucleotides, as from X-ray diffraction, are fully supported by MEP maps. But the main finding was that MD-driven dissection of the various contributions revealed a dominance of the entropically favored chelate H-bonding between AGA’s central amide system and U2869. In contrast, the X-ray diffraction assignment of C5-OH H-bonding to U2873 is not supported. Along similar lines it was found that interactions of the ribosome with the structural analog CEAA, where chlorine and ethyl replace AGA’s bromine and methyl, differ markedly, except as to the chelate bonding with U2869, which persists as a character of the class. This should be useful in the invention of improved translation inhibitors in the agelastatin class.

Structures and properties of [Ag(Ag2S)n]+ clusters with n = 1–9: a density functional theory study

Silver sulfide clusters with size less than 2 nm are of much interest in photoelectric devices, such as photoconductive devices, infrared detectors and superconductors. The electronic structures of [Ag(Ag2S)n]+ (n = 1–9) clusters are investigated using the combined method of genetic algorithm (GA) and density functional theory (DFT). Results reveal that S atoms prefer to be at the tip of the structure, and Ag atoms tend to form S-Ag-S unit between two S atoms. With the increase of cluster size, the open structure evolves into closed centre-hollow structure. According to the stability analysis, [Ag(Ag2S)6]+ is a magic number cluster due to its high HOMO-LUMO gap, big average energy and high second-order energy difference. Ag-S bonds, S-Ag-S and triangular Ag3S3 units play key roles in stabilizing [Ag(Ag2S)n]+ clusters. According to the electron affinity energy analysis, the clusters are easier to get electrons when n = 1, 3, 5 and 9. Based on the charge analysis of the studied clusters, the charges on Ag and S atoms are positive and negative, respectively, which indicates that the charge transfer from Ag to S occurs in cluster. Infrared and Raman spectra are dependent on the symmetries of the clusters. The molecular orbitals of [Ag(Ag2S)6]+ and [Ag(Ag2S)8]+ present superatomic properties. We hope that the clusters studied here could provide valuable data for future experimental and theoretical study of cationic silver sulfide clusters.

Chemical reactivity theory (CRT) study of small drug-like biologically active molecules

New biochemical screening and design based technology are used to identify the small molecules in targeting RNA. These approaches has develop potential drug like small molecule for RNA-targeted therapeutics. Chemical Reactivity Theory (CRT) is used to study these drug-like, biologically active small molecules that target RNA. Twenty two small molecules based on structure (1–6), information (7–9), fragment (10–19), small molecular microarrays (20), and use of phenotypic assays (21–22) are selected for the studies of several DFT-based global reactivity and local reactivity descriptors to provide complete explanation for the reactivity of these complexes by chemical reactivity method. Higher HOMO-LUMO gap indicated the structural stability for the studied complexes. The complexes reflect greater thermodynamic stability. Further the results predicted that high aromaticity and hardness are measures of high stability and low reactivity for the studied complexes. It was observed that a good, more reactive, nucleophile can be described by a lower value of μ, ω while a good electrophile can be described by a high value of μ, ω. TDDFT results predicted that few complexes can be used as fluorescent biomarkers as their emission wavelength lies in the visible region. Communicated by Ramaswamy H. Sarma

Systematic study on the structures and properties of (Ag2S)n (n = 1-8) clusters.

Silver sulfide is a famous semiconductor, which can be used in many areas. Understanding the size evolution of silver sulfide clusters is useful in controlling their size to improve their properties in applications. The structures of (Ag2S)n (n = 1-8) clusters are explored using a combined method of genetic algorithm (GA) and density functional theory (DFT). The TPSSh/def2-tzvp(Ag)/6-311G(d)(S) method has been used to optimize the structures. The re-optimized structures and refined energies are computed at PBE0/Lanl2tz(Ag)/6-311G(d,p)(S) level according to the benchmark calculations. The global minimum (GM) structures, HOMO and LUMO frontier orbitals, density of states, ionization potentials, electron affinity energies, noncovalent interactions, and natural populations of the clusters have been studied. The clusters evolve from open to cage structures when n varies from 1 to 8. A triangular Ag3S3 unit is found to be an important building block, which can construct the global minimum structures of (Ag2S)n (n = 3-8) clusters. When n > 6, quadrangular Ag4S4 rings present in (Ag2S)n clusters. (Ag2S)6 and (Ag2S)8 clusters are in hollow conformation, and both of which have special stability because of their high HOMO-LUMO gaps, high ionization potentials, and Ag⋯Ag attractive interactions in them. Graphical abstract.

Synthesis and reactivity/stability study of double-functionalizable strained trans-cyclooctenes for tetrazine bioorthogonal reactions

Abstract The unique ability of the bioorthogonal pairs to withstand and unaffect biological processes while maintaining high selectivity towards each other sparked the interest in better probing and controlling biological functions. In early years, trans-cyclooctene (TCO)/tetrazine ligation readily standed out by encompassing most of the bioorthogonal criteria such as its excellent biocompatibility, selectivity and efficiency, and as a result of high HOMO-LUMO gap. Modifications on the TCO scaffold such as cyclopropanation render bicyclononene-based TCOs with high enhancement of its reactivity, whereas other modifications focused on improving the solubility, stability, or enabling the scaffold to act as click-to-release drug delivery system. The implementation of facile methods to enhance its versatility is essential for potentiating drug-delivery strategies and expanding the dynamic range of bioorthogonal on/off control. Considering the remarkable properties of bicyclononene-based TCOs we envisioned that the incorporation of an additional vector for functionalization at the cyclopropane moiety could allow access to more complex and double-functionalized TCO probes. Herein we report the synthesis and study of a double-functionalizable strained trans-cyclooctenes for tetrazine bioorthogonal reactions.

Superalkalis as a source of diffuse excess electrons in newly designed inorganic electrides with remarkable nonlinear response and deep ultraviolet transparency: A DFT study

Recently, significant progress is observed in the design and synthesis of nonlinear optical materials due to their optoelectronic and biomedical applications. In this report, a series of inorganic electrides (Li2F@Al12P12, Li3O@Al12P12 and Li4N@Al12P12) are designed by doping of Al12P12 nanocluster with superalkalis (Li2F, Li3O and Li4N) and studied through density functional theory (DFT) for their geometrical, electronic and nonlinear optical properties. Computational results indicated that these superalkalis doped complexes possess high stability and low HOMO-LUMO gaps. Interaction energies reveal that adsorption of Li4N on Altop site of Al12P12 results in highly stable structure (isomer J), where superalkali is strongly chemisorbed on the nanocage (Eint. = −105.13 kcal mol−1). Moreover, the lowest HOMO-LUMO gap is also observed for J isomer of Li4N@Al12P12 (0.44 eV), compared to 0.94 eV for alkali metal doped Al12P12 nanocage and 3.36 eV for pure nanocage. Doping of superalkali on aluminum phosphide nanocage can bring considerable increase in first hyperpolarizabilities (βo) response of the nanocage along with deep ultraviolet transparency. The first hyperpolarizability (βo) for isomer J of Li4N@Al12P12 is 6.25 × 104 au. This study may provide an effective strategy to design high performance NLO materials from stable inorganic electrides.

Impact of silicon dopant on the absorption and Raman spectroscopy of metal clusters with seven atoms

ABSTRACTThe structural, optical, and magnetic properties of silicon-doped copper, silver, and gold clusters with D5h symmetry and seven atoms have been investigated using density functional theory calculations. The global optimized structures of silicon-doped metal clusters are predicted to have a higher HOMO–LUMO gap and higher binding energy than nondoped metal clusters, and nondoped metal clusters have a higher magnetic moment than silicon-doped metal clusters. The silicon doping in metal clusters changes absorption strength and range of absorption wavelength. The silicon dopant also provides a significant impact on the absorption and Raman spectroscopy of nondoped metal clusters. The Raman activities of silicon-doped and nondoped metal clusters are helpful in determining the size and structure of the experimental clusters.

1,1-Difluoronaphthalen-2(1H)-ones as building blocks for fluorinated tetraphenes

1,1-Difluoronaphthalen-2(1H)-ones were used as building blocks for synthesis of functionalized fluorinated tetraphenones via Diels-Alder reaction. Two effective methods of tetraphenone reductive aromatization were proposed. Fully aromatic stable fluorinated tetraphene derivative with high solubility and HOMO-LUMO gap of 3.08 eV was obtained.

Control of Rectification in Molecular Junctions: Contact Effects and Molecular Signature.

Thin layers of oligomers with thickness between 7 and 9 nm were deposited on flat gold electrode surfaces by electrochemical reduction of diazonium reagents, then a Ti(2 nm)/Au top contact was applied to complete a solid-state molecular junction. The molecular layers investigated included donor molecules with relatively high energy HOMO, molecules with high HOMO-LUMO gaps and acceptor molecules with low energy LUMO and terminal alkyl chain. Using an oligo(bisthienylbenzene) based layer, a molecule whose HOMO energy level in a vacuum is close to the Fermi level of the gold bottom electrode, the devices exhibit robust and highly reproducible rectification ratios above 1000 at low voltage (2.7 V). Higher current is observed when the bottom gold electrode is biased positively. When the molecular layer is based on a molecule with a high HOMO-LUMO gap, i.e., tetrafluorobenzene, no rectification is observed, while the direction of rectification is reversed if the molecular layer consists of naphtalene diimides having low LUMO energy level. Rectification persisted at low temperature (7 K), and was activationless between 7 and 100 K. The results show that rectification is induced by the asymmetric contact but is also directly affected by orbital energies of the molecular layer. A "molecular signature" on transport through layers with thicknesses above those used when direct tunneling dominates is thus clearly observed, and the rectification mechanism is discussed in terms of Fermi level pinning and electronic coupling between molecules and contacts.

Stabilities, electronic and magnetic properties of Cu-doped nickel clusters: a DFT investigation

ABSTRACTIn this paper, we investigate the electronic and magnetic properties of Cu-doped nickel clusters by means of density functional theory. The stabilities of these clusters have also been studied in terms of the binding energies, second-order difference of energies, fragmentation energies and HOMO–LUMO energy gaps. The obtained results reveal that the N4Cu, N5Cu and Ni7Cu clusters are found to be more stable that than all other clusters. Higher HOMO–LUMO gap was observed for Ni5Cu cluster (2.265 eV), indicating its higher chemical stability. A half-metallic behaviour has also been observed for the NinCu clusters, which suggests that these clusters can be employed as nanocatalysts for several catalytic processes, particularly for hydrogenation and dehydrogenation reactions. The magnetism calculations show that the magnetic moment is mostly located on the Ni atoms, and the contribution of the Cu atom to the total magnetic moment in the NinCu clusters is very small. Furthermore, partial density of states analysis indicates that the 3d orbitals in Ni atoms are mostly responsible for the magnetic behaviour of these clusters, and the s orbitals have a very little contribution to the total magnetic moment.

Metal Chalcogenide Clusters with Closed Electronic Shells and the Electronic Properties of Alkalis and Halogens.

Clusters with filled electronic shells and a large gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are generally energetically and chemically stable. Enabling clusters to become electron donors with low ionization energies or electron acceptors with high electron affinities usually requires changing the valence electron count. Here we demonstrate that a metal cluster may be transformed from an electron donor to an acceptor by exchanging ligands while the neutral form of the clusters has closed electronic shells. Our studies on Co6Te8(PEt3)m(CO)n (m + n = 6) clusters show that Co6Te8(PEt3)6 has a closed electronic shell and a low ionization energy of 4.74 eV, and the successive replacement of PEt3 by CO ligands ends with Co6Te8(CO)6 exhibiting halogen-like behavior. Both the low ionization energy Co6Te8(PEt3)6 and high electron affinity Co6Te8(CO)6 have closed electronic shells marked by high HOMO-LUMO gaps of 1.24 and 1.39 eV, respectively. Further, the clusters with an even number of ligands favor a symmetrical placement of ligands around the metal core.

Pu@C24: A New Example Satisfying the 32-Electron Principle

A transition in point group symmetry from C2 to D6d in the classical cage isomer of C24 cluster is observed after encapsulation of a plutonium atom within it. This encapsulation leads to highly stable Pu@C24 cluster, which is well supported by the structural, energetic, and thermodynamic aspects. This study has been carried out with first five low-lying isomers of C24 fullerene, among which one is classical fullerene consisting of only five- and six-membered rings (MR) and remaining four isomers are nonclassical fullerene consisting of five and six MR along with varying number of four MR. The structural and stability aspects are investigated extensively for the Pu@C24 cluster. For the purpose of comparison we have also considered some other lanthanides/actinides with 8 valence electrons (Cm2+, Sm, and Gd2+) and investigated the encapsulation process into different C24 isomers. It has been found that the Pu@C24 cluster is the most stable one among all the metallofullerenes considered here. For Pu@C24, it has been observed that HOMO–LUMO gap is changed from 1.83 to 3.26 eV after encapsulation of a Pu atom into the bare classical C24 cage. It is interesting to note that the bare C24 nonclassical (C2 symmetry) cluster is the most stable one; however, after encapsulation, the classical isomer becomes the most stable with significant energy differences. The detail vibrational and electronic spectral studies have also been carried out for the classical Pu@C24 metallofullerene. High HOMO–LUMO gaps and positive binding energy values for the Pu@C24 clusters and negatives values of reaction enthalpy and free energy corresponding to the encapsulation process indicate toward possible formation of Pu@C24 and subsequent experimental detection. High stability of the Pu@C24 cluster can be rationalized through the fulfilment of 32 valence electron count corresponding to the fully occupied spdf shells for the central metal atom.

Syntheses, Spectroscopic and DFT Studies of Two New D‐π‐A Compounds

Two novel 1,3‐dithiole‐2‐ylidene derivatives with a push–pull structures, 3‐(4,5‐dicarbomethoxy‐1,3‐dithiol‐2‐ylidene)naphthopyranone 1 and 3‐(4,5‐dimethylthio‐1,3‐dithiol‐2‐ylidene)naphthopyranone 2, have been synthesized and characterized by 1H NMR, IR, MS. The UV–vis spectra of 1, 2 in CH2Cl2, the lowest‐energy absorption bands, are centered at 280, 316, and 430 nm for 1 and 284, 317, and 450 nm for 2, respectively, which are caused by the HOMO → LUMO single electron promotion. Furthermore, the steady‐state fluorescence originating states of 1, 2 from the excited charge‐transfer were observed. To estimate the position and energies of frontier orbitals for 1, 2, DFT calculations were performed using the Gaussian 03 program at the B3LYP/6‐31 G* level. The calculated vertical excitation energies are in good agreement with the experimental data. The high HOMO–LUMO gaps of 1 (3.08 eV) and 2 (3.00 eV) indicate high kinetic stability of the title compounds.

High Charge Delocalization and Conjugation in Oligofuran Molecular Wires

The extent of charge delocalization and of conjugation in oligofurans and oligothiophenes was studied by using mixed valence systems comprising oligofurans and oligothiophenes capped at both ends by ferrocenyl redox units. Using electrochemical, spectral, and computational tools, we find strong charge delocalization in ferrocene-capped oligofurans which was stronger than in the corresponding oligothiophene systems. Spectroscopic studies suggest that the electronic coupling integral (H(ab)) is roughly 30-50 % greater for oligofuran-bridged systems, indicating better energy matching between ferrocene units and oligofurans. The distance decay constant (damping factor), β, is similar for oligofurans (0.066 A(-1)) and oligothiophenes (0.070 A(-1)), which suggests a similar extent of delocalization in the bridge, despite the higher HOMO-LUMO gap in oligofurans. Computational studies indicate a slightly larger extent of delocalization in furan-bridged systems compared with thiophene-bridged systems, which is consistent with oligofurans being significantly more rigid and less aromatic than oligothiophenes. High charge delocalization in oligofurans, combined with the previously reported strong fluorescence, high mobility, and high rigidity of oligofuran-based materials makes them attractive candidates for organic electronic applications.

Optical and magnetic properties of Cu-doped 13-atom Ag nanoclusters

The structural, optical and magnetic properties of Ag13, Ag12Cu1 and Cu13 clusters have been investigated using density functional theory calculations. The global minimum of the Ag12Cu1 cluster is predicted to be cuboctahedral (COh) core–shell structure with Oh point group symmetry while the icosahedral (Ih) core–shell isomer has a higher HOMO–LUMO gap and higher magnetic moment. The optical absorption spectrum of the Ih Ag12Cu1 has three absorption peaks at 2.17, 2.41 and 2.65eV, compared with that the COh Ag12Cu1 has one main absorption peak at 2.51eV. The characteristics in electronic density of states (DOSs) show that Ih core–shell Ag12Cu1 has ferromagnetic properties like pure Au13, Ag13 nanoclusters. The sizable split between spin up and spin down DOS of d states in the inner Cu atom and sp states in the outer Ag atoms bring in large magnetic moment to Ih Ag12Cu1 cluster.

P-Carborane-Bridged Bipyridine Ligands for Energy Transfer between Two Iridium Centers

Two iridium(III) complexes displaying for one a high HOMO-LUMO gap and for the other a weaker gap were linked in a controlled and logical manner to closo-p-carborane spacers. The bridging ligand is composed of 5-ethynyl-2,2'-bipyridine units, and the peripherical Ir-ligands are orthometalated 2',4'-difluoro-2-phenylpyridine (dfppy) (λ(abs) at 400 nm for the "Ir(dfppy)2(bpy')") for the energy donor fragment and dibenzo[a,c]phenazine (dbpz) (λ(abs) at 525 nm for "Ir(dbpz)2(bpy')") for the energy acceptor fragment.Redox, spectroscopic, and photophysical properties for models and the donor-carborane-acceptor complex were determined. Efficient energy transfer from the "Ir(dfppy)2(bpy')" moiety to the "Ir(dbpz)2(bpy')" fragment is occurring with a rate constant of 3.3 × 10(8) s(-1) despite weak electronic coupling through the inert p-carborane spacer. From flash photolysis experiments it is shown that, by excitation of the donor, a low lying triplet state localized on the acceptor bridging ligand side is formed which decays by conversion to the (3)MLCT of the acceptor fragment which phosphoresces at 644 nm.