Highest Occupied Molecular Orbital-lowest Unoccupied Molecular Orbital Research Articles

Ab-initio and DFT methodologies for computing hyperpolarizabilities and susceptibilities of highly conjugated organic compounds for nonlinear optical applications

In this talk, after a short introduction on the methodologies used for computing dipole polarizability (α), second and third-order hyperpolarizability and susceptibility; the results of theoretical studies performed on density functional theory (DFT) and ab-initio quantum mechanical calculations of nonlinear optical (NLO) properties for a few selected organic compounds and polymers will be explained. The electric dipole moments (μ) and dispersion-free first hyperpolarizabilities (β) for a family of azo-azulenes and a styrylquinolinium dye have been determined by DFT at B3LYP level. To reveal the frequency-dependent NLO behavior, the dynamic α, second hyperpolarizabilities (γ), second (χ(2)) and third-order (χ(3)) susceptibilites have been evaluated using time-dependent HartreeFock (TDHF) procedure. To provide an insight into the third-order NLO phenomena of a series of pyrrolo-tetrathiafulvalene-based molecules and pushpull azobenzene polymers, two-photon absorption (TPA) characterizations have been also investigated by means of TDHF. All computed results of the examined compounds are compared with their previous experimental findings and the measured data for similar structures in the literature. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by configuration interaction (CI) method. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO–LUMO band gaps have been revealed by DFT at B3LYP level for azo-azulenes, styrylquinolinium dye, push–pull azobenzene polymers and by parametrization method 6 (PM6) for pyrrolo-tetrathiafulvalene-based molecules.

Metal-Organic Frameworks as Promising Photosensitizers for Photoelectrochemical Water Splitting.

Ti-based metal-organic frameworks (MOFs) are demonstrated as promising photosensitizers for photoelectrochemical (PEC) water splitting. Photocurrents of TiO2 nano wire photoelectrodes can be improved under visible light through sensitization with aminated Ti-based MOFs. As a host, other sensitizers or catalysts such as Au nanoparticles can be incorporated into the MOF layer thus further improving the PEC water splitting efficiency.

Ab initio investigation of 2,2′‐bis(4‐trifluoromethylphenyl)‐5,5′‐bithiazole for the design of efficient organic field‐effect transistors

The initial molecular structure of 2,2′‐bis(4‐trifluoromethylphenyl)‐ 5,5′‐bithiazole has been optimized in the ground state using density functional theory (DFT). The distribution patterns of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have also been evaluated. To shed light on the charge transfer properties, we have calculated the reorganization energy of electron λe, the reorganization energy of hole λh, adiabatic electron affinity (EAa), vertical electron affinity (EAv), adiabatic ionization potential (IPa), and vertical ionization potential (IPv) using DFT. Based on the evaluation of hole reorganization energy, λh, and electron reorganization energy, λe, it has been predicted that 2,2′‐bis(4‐trifluoromethylphenyl)‐5,5′‐bithiazole would be a better electron transport material. Finally, the effect of electric field on the HOMO, LUMO, and HOMO–LUMO gap were observed to check its suitability for the use as a conducting channel in organic field‐effect transistors. © 2015 Wiley Periodicals, Inc.

Interconversion between Superatomic 6-Electron and 8-Electron Configurations of M@Au₂₄(SR)₁₈ Clusters (M = Pd, Pt).

The exceptional stability of thiolate-protected Au25 clusters, [Au25(SR)18](-), arises from the closure of superatomic electron shells, leading to a noble-gas-like 8-electron configuration (1S(2)1P(6)). Here we present that replacing the core Au atom with Pd or Pt results in stable [MAu24(SR)18](0) clusters (M = Pd, Pt) having a superatomic 6-electron configuration (1S(2)1P(4)). Voltammetric studies of [PdAu24(SR)18](0) and [PtAu24(SR)18](0) reveal that the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of these clusters are 0.32 and 0.29 eV, respectively, indicating their electronic structures are drastically altered upon doping of the foreign metal. Density functional investigations confirm that the HOMO-LUMO gaps of these clusters are indeed smaller, respectively 0.33 and 0.32 eV, than that of [Au25(SR)18](-) (1.35 eV). Analysis of the optimized geometries for the 6-electron [MAu24(SR)18](0) clusters shows that the MAu12 core is slightly flattened to yield an oblate ellipsoid. The drastically decreased HOMO-LUMO gaps observed are therefore the result of Jahn-Teller-like distortion of the 6-electron [MAu24(SR)18](0) clusters, accompanying splitting of the 1P orbitals. These clusters become 8-electron [MAu24(SR)18](2-) clusters upon electronic charging, demonstrating reversible interconversion between the 6-electron and 8-electron configurations of MAu24(SR)18.

Geometries and Electronic Properties of Transition Metal Hafnium-Doped Boron Clusters: A Computational Investigation

The geometries, stabilities, electronic properties, and bonding properties of the Hf-doped boron clusters at the size of n = 5–11 have been investigated systematically by using density functional theory. Emphasis is placed on studies that focus on the growth-pattern behaviors, dipole moments, fragmentation energies, aromatic properties, charge-transfer characteristics, and highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps. The optimized geometries show that the aromatic Hf-encapsulated negative Bn structures emerges as n = 10. The calculated fragmentation energies manifest that the magic numbers of stabilities are HfBn (n = 6, 9, and 11) and the HfB11 is the most stable isomer of all different sized clusters. Natural population analysis shows that the charges transfer from Hf atom to boron framework. It should be pointed out that the remarkable charge-transfer features of HfBn clusters are obviously different from those of transitional metal (TM = W and Mo) doped Bn clusters. In addition, the calculated HOMO-LUMO gaps indicate that the HfBn (n = 5, 9, and 11) clusters have dramatically enhanced stabilities; meanwhile, the cage-like HfB11 cluster is revealed and has the largest chemical hardness.

Molecules relevant for organic photovoltaics: a range-separated density functional study

Accurate determination of both fundamental and optical gap is necessary for designing molecules relevant for organic photovoltaics. Here, we study how range-separated density functionals reproduce frontier orbital energies, HOMO (highest occupied molecular orbital)–LUMO (lowest unoccupied molecular orbital) gaps, and optical gaps for molecules relevant for organic photovoltaics. In this study, we consider 12 different range-separated density functional for computing HOMO energy, HOMO–LUMO gap, and optical gap which are compared with available experimental and reported GW values. We found that the reproduction of desired photovoltaic properties primarily depend on range separation parameter. Moreover, the tested functionals are comparable with OT-BNL functional.

Density functional theory (DFT) investigations on doped fullerene with heteroatom substitution

Structures and stabilities of dodecahedral fullerene C19X (X=Ni, Ti) and C20 have been investigated by quantum chemical calculations based on density functional theory. The geometrical structures, relative stabilities, dielectric constant of the doped cages were studied systematically and compared with those of the fullerene C20 cage. A series of dodecahedral functionalized derivatives have been studied at the B3LYP/6-31G level of density functional theory (DFT). The relative and formation energies of compounds, Mulliken charges, occupancy, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), the HOMO–LUMO band gap and chemical potential (μ) were calculated. The doping effect is discussed in terms of the change in the CC bond length and total dipole moment. The obtained result indicates that the CC bond length increases as a result of doping. The NBO analysis showed that there is a hyper conjugative interaction between the hetero atoms such as titanium and nickel lone-pair electron of doped fullerene with bonding and antibonding (σ∗) orbital of carbon atom of fullerene. The stability of the molecule, arising from charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The nucleus – independent that more negative NICS values in doped fullerene than those of C20. The condensed Fukui Function and the newly introduced the atomic descriptors S (fk) to determine the local reactive sites of the molecular systems during electrophilic, nucleophilic and radical attacks have been calculated for the fullerene C20 compound.

Electro-optical and charge injection investigations of the donor-π-acceptor triphenylamine, oligocene–thiophene–pyrimidine and cyanoacetic acid based multifunctional dyes

The corner stone of present study is to tune the electro-optical and charge transport properties of donor-bridge-acceptor (D-π-A) triphenylamine (TPA) derivatives. In the present investigation, an electron deficient moiety (pyrimidine), electron-rich moiety (thiophene) and oligocene (benzene, naphthalene, anthracene, tetracene and pentacene) have been incorporated as π-spacer between the donor TPA unit and cyanoacetic acid acceptor and anchoring group. The elongation of bridge usually affects the energy levels, i.e., higher the highest occupied molecular orbital (HOMO) while lower the lowest unoccupied molecular orbital (LUMO) thus reduces the HOMO–LUMO energy gap. The lowered LUMO energy levels of cyano-{2-[6-(4-diphenylamino-phenyl)-pyrimidin-4-yl]-tetraceno[2,3-b]thiophen-8-yl}-acetic acid (TPA-PTT4) and cyano-{2-[6-(4-diphenylamino-phenyl)-pyrimidin-4-yl]-pentaceno[2,3-b]thiophen-9-yl}-acetic acid (TPA-PPT5) dyes revealed that electron injected from dye to semiconductor surface might be auxiliary stable resulting in impediment of quenching. The broken co-planarity between the π-spacer conceiving LUMO and the TPA moiety would help to impede the recombination process. Moreover, it is expected that TPA derivatives with the tetracenothiophene and pentacenothiophene moieties as π-bridge would show better photovoltaic performance due to lowered LUMO energy level, higher electronic coupling constant, light harvesting efficiency and electron injection values.

Characterization and Density Functional Theory Optimization of a Simultaneous Binder (FSG-XO) of Two Different Species Exploiting HOMO–LUMO Levels: Photoelectronic and Analytical Applications

A cost-time effective mesoporous ion-exchange material (FSG-XO) has been synthesized by immobilizing xylenol orange on functionalized silica gel. Its spatially separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have been used for the simultaneous sorption of two different metal centers at their respective high and low oxidation states. The characterization of its corresponding nanomaterial, {Si[OSi]p=2–4[OH]m=2–0 xH2O}n[−Si(CH3)2–NH–C6H4–N═N–XO]4 has been assessed by a set of sophisticated analysis. FSG-XO possesses high SABET (346.22 m2/g), PV (0.431549 cm3/g), uniform pore size (width, 47.1; and diameter, 50.3 nm), high chemical (4 M HNO3) and thermal stability (140 °C), high level of reusability (<1000 cycles), high BTC (240 μM g–1) and high PF (111). The spatially well separated (931.6 pm) HOMO (−6.1631 eV)–LUMO (4.2795 eV) with a band gap of 10.44 eV denies any sort of charge recombination and proves its utility as a light emitting diode source and it shows its applicability as good donor–acceptor organic electronic device. The extractor exhibits its outstanding performance in binding molecular I2 at its LUMO and enhances its breakthrough capacity by the same amount as obtained after the full saturation of HOMO by an electrophile (Zn(II)).

Computational Study on Ammonia Adsorption on the X 12 Y 12 Nano-Clusters (x = B, Al and Y = N, P)

The adsorption of ammonia (NH 3 ) on four X 12 Y 12 (X = B, Al and Y = N, P) nano-cages was investigated using density functional theory calculations. Changes in Gibbs free energy, adsorption energy, frequency modes, natural bond orbitals, molecular electrostatic potential surfaces and density of states were explored. It was found that the relative order of the acidity for the surfaces is: Al 12 N 12 > Al 12 P 12 > B 12 N 12 > B 12 P 12 . In the case of Al 12 N1 2 , hybridization and lower electron density of the adsorbing atom overcome the disadvantage of high HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) energy gap (E g ); therefore, this cage becomes the most favourable for the adsorption of NH 3 . We found that changes in the electronic properties of the clusters are negligible after the adsorption process. Also, the value of E g increases with the increase in the Hartree-Fock exchange per cent of the density functional.

AIM and NBO analyses on the interaction between SWCNT and cyclophosphamide as an anticancer drug: A density functional theory study

In this work, the molecular structures of single-walled carbon nanotube (SWCNT), cyclophosphamide and cyclophosphamide–SWCNT complex were optimized B3LYP/6–31G* level of theory. The nanotube used in this study was a (5,5) SWCNT including 150 C atoms. The NBO analysis showed that the transfer electron can be occurred from the lone pair of oxygen (donor atom) in the cyclophosphamide to the σ* or π* orbitals of the carbon atoms (acceptor atoms) in the SWCNT. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and energy gap (HOMO–LUMO) were calculated for the studied structures and the results indicated the stability of the complex. In addition, the calculated chemical shift isotropy (σ) and the chemical shift anisotropy (Δσ) confirmed the interaction between cyclophosphamide and SWCNT. Also, the results of the atoms in molecule (AIM) theory indicated that the H 145– O 164 bond is a partial covalent bond.

Density functional theory study on silver clusters using dimers, trimers, and tetramers as building units

We systematically investigate growth patterns of small silver clusters, Agn (n ≤ 10), using density functional theory (DFT) and time-dependent density functional theory (TDDFT), considering Ag2, Ag3, and Ag4 as basic building units. Nearest-neighbor distances increase gradually with increasing n. Compared with an earlier study, where the clusters were developed by adding one atom at a time, the clusters derived in this investigation had considerably higher computed binding energies, confirming increased stability and suggesting possible growth patterns using these basic units. We used TDDFT methods to simulate the ultraviolet–visible spectra of the silver clusters, which are in good agreement with the reported experimental absorption spectrum of Ag nanoparticles. Our study indicates that the clusters formed with units of Ag3 tend to form more reactive clusters, particularly if an odd number of atoms is involved. Further, the higher level of computations employed gives better insight into the process of particle growth. The disproportionation energies of clusters built using this scheme are compared with those built one atom at a time. Mulliken population analysis of the distributions indicates the presence of polarities among the atoms in some of the cluster isomers, suggesting sites of increased activity. In addition, patterns established for the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and HOMO–LUMO energy gaps may be used to model stable clusters with modified optoelectrical properties.

Vibrational spectra (experimental and theoretical), molecular structure, natural bond orbital, HOMO–LUMO energy, Mulliken charge and thermodynamic analysis of N′-hydroxy-pyrimidine-2-carboximidamide by DFT approach

The FT-IR, FT-Raman, 1H, 13C NMR and UV–Visible spectral measurements of N′-hydroxy-pyrimidine-2-carboximidamide (HPCI) and complete analysis of the observed spectra have been proposed. DFT calculation has been performed and the structural parameters of the compound was determined from the optimized geometry with 6-311+G(d,p) basis set and giving energies, harmonic vibrational frequencies and force constants. The results of the optimized molecular structure are presented and compared with the experimental. The geometric parameters, harmonic vibrational frequencies and chemical shifts were compared with the experimental data of the molecule. The title compound, C5H6N4O, is approximately planar, with an angle of 11.04 (15)°. The crystal structure is also stabilized by intermolecular N–H⋯O, N–H⋯N, O–H⋯N, C–H⋯O hydrogen bond and offset π–π stacking interactions. The influences of hydroxy and carboximidamide groups on the skeletal modes and proton chemical shifts have been investigated. Moreover, we have not only simulated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) but also determined the transition state and band gap. The kinetic, thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intermolecular electronic interactions and their stabilization energy. The thermodynamic properties like entropies and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized structure.

Molecular Heterojunctions of Oligo(phenylene ethynylene)s with Linear to Cruciform Framework

Electrical transport properties of molecular junctions are fundamentally affected by the energy alignment between molecular frontier orbitals (highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO)) and Fermi level (or work function) of electrode metals. Dithiafulvene (DTF) is used as substituent group to the oligo(phenylene ethynylene) (OPE) molecular wires and different molecular structures based on OPE3 backbone (with linear to cruciform framework) are achieved, with viable molecular orbitals and HOMO–LUMO energy gaps. OPE3, OPE3–DTF, and OPE3–tetrathiafulvalene (TTF) can form good self‐assembled monolayers (SAMs) on Au substrates. Molecular heterojunctions based on these SAMs are investigated using conducting probe–atomic force microscopy with different tips (Ag, Au, and Pt) and Fermi levels. The calibrated conductance values follow the sequence OPE3–TTF &gt; OPE3–DTF &gt; OPE3 irrespective of the tip metal. Rectification properties (or diode behavior) are observed in case of the Ag tip for which the work function is furthest from the HOMO levels of the OPE3s. Quantum chemical calculations of the transmission qualitatively agree with the experimental data and reproduce the substituent effect of DTF. Zero‐bias conductance, and symmetric or asymmetric couplings to the electrodes are investigated. The results indicate that improved fidelity of molecular transport measurements may be achieved by systematic studies of homologues series of molecular wires applying several different metal electrodes.

A Computational Investigation on Boron Clusters with W Impurity

Geometries associated with relative stabilities and charge-transfer as well as growth patterns and energy gaps of the W-doped boron clusters have been investigated systematically by using density functional theory. The critical size of W-encapsulated Bn structures emerges as n = 9 and 10, the evaluated relative stabilities in term of the calculated fragmentation energies reveal that the WB8 has enhanced stabilities over their neighboring clusters. Furthermore, the calculated polarities of the WBn reveal that the hypercoordinated planar WB10 wheels are the weakened polar molecules, and WB9 and WB11 rings are non polar molecules. Additionally, the WB9 and WB10 clusters with smaller highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps are supposed to be stronger chemical activity, while WB11 has large HOMO-LUMO gap with stronger geometrical stabilities. Moreover, the recorded natural populations show that the charges transfer from boron framework to W atom and W stabilizes the WBn (n = 8–11). It should be pointed out that the remarkable charge-transfer features of WBn clusters are quite similar to those of transitional metal (TM) doped Sin clusters. In addition, the formation of TM@Bn depends on the TM impurity.

The fate of NHC-stabilized dicarbon.

The attempted synthesis of NHC-stabilized dicarbon (NHC=C=C=NHC) through deprotonation of a doubly protonated precursor ([NHC-CH=CH-NHC](2+) ) is reported. Rather than deprotonation, a clean reduction to NHC=CH-CH=NHC is observed with a variety of bases. The apparent resistance towards deprotonation to the target compound led to a reinvestigation of the electronic structure of NHC→CC←NHC, which showed that the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) gap is likely too small to allow for isolation of this species. This is in contrast to the recent isolation of the cyclic alkylaminocarbene analogue (cAAC=C=C=cAAC), which has a large HOMO-LUMO gap. A detailed theoretical study illuminates the differences in electronic structures between these molecules, highlighting another case of the potential advantages of using cAAC rather than NHC as a ligand. The bonding analysis suggests that the dicarbon compounds are well represented in terms of donor-acceptor interactions L→C2 ←L (L=NHC, cAAC).

Crystal Growth, Structural Analysis, Characterization, Conformational Stability and Quantum Chemical Calculation of the Pharmaceutical Compound ? P-Arsanilic Acid

p-Arsanilic acid ,which is otherwise known as 4-amino phenyl arsonic acid, is a bioactive compound. Single crystals of p-Arsanilic acid (pAsA) are grown successfully under slow evaporation technique. The crystallinity and parameters of the grown crystal are determined with the powder x-ray diffraction result. The functional groups are characterized by FTIR and FT-RAMAN spectra. The UV spectrum reveals its application in the optoelectronic field. The molecular structure of the title compound is studied using density functional theory (DFT). The vibrational frequencies and the potential energy distribution (PED) are calculated using DFT/B3LYP 6-31+G** basis set. The stability of the molecule is determined by various conformers in the computational method. The HOMO-LUMO (Highest Occupied Molecular Orbital – Lowest Unoccupied Molecular Orbital) charge transfer and Non-Linear Optical (NLO) property determination were carried out. The electrophilic and nucleophilic attack of the molecule is studied using the MEP (Molecular Electrostatic Potential). The theoretical prediction of the thermodynamic properties helps in analysing the future application of the title compound.

Design of Methane Hydrate Inhibitor Molecule Using Density Functional Theory

A strategy for designing methane hydrate inhibitor molecule has been established depending upon geometrical parameters, interaction energy, highest occupied molecular orbital (HOMO)—lowest unoccupied molecular orbital (LUMO) structures and energies, natural bond orbital analysis, potential energy curve, Mullikan charge, IR intensity and red shift. One methane hydrate inhibitor molecule namely 2,2′-oxydipropane-1, 3-diol has been designed based on the established design strategy. Theoretical study of effectiveness of the designed inhibitor molecule has been performed for methane hydrate pentagonal dodecahedron cage (1CH4@512) using WB97XD/6-31++G(d,p). Calculated geometrical parameters, interaction energies and HOMO–LUMO study indicate that reduction of the strength of hydrogen bonded network of 1CH4@512 cage is more by designed inhibitor 2,2′-oxydipropane-1,3-diol compared to conventional thermodynamic inhibitor (methanol) and consequently 2,2′-oxydipropane-1,3-diol can be more effective methane hydrate inhibitor than methanol.

Emission spectra dependence on voltage and emissive layer layout in organic light-emitting diodes

Based on the device structure of indium tin oxide (ITO)/N,N′-diphenyl-N,N′-bis(1-naphthyl-phenyl)-1,1′-biphenyl-4,4′-diamine (NPB)/4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)/tris (8-hydroxy quinoline) aluminum (Alq3)/NPB/bathocuproine (BCP)/Al, the variation of emissive spectra with voltage and emissive unit (DCJTB/Alq3/NPB) parameters has been investigated. All electroluminescent spectra contain two components: blue emission from NPB and red emission of DCJTB. The Alq3 emission is not observed due to its relative shallow LUMO (the lowest unoccupied molecular orbital) and deep HOMO (the highest occupied molecular orbital). The emission of NPB is increased with voltages as well as the thickness of NPB and Alq3 for more holes escape from DCJTB and get in NPB to recombine with electrons.

Quantum chemistry study on nonlinear optical properties of hemicyanine dye derivatives with different electron donor groups

We have designed 9 hemicyanine dye derivatives with different electron donor groups. The geometric structures are optimized by using density functional theory approach at B3LYP/6-31G(d,p) level of theory. The static first hyperpolarizability, absorption spectra and molecular frontier orbital properties of hemicyanine dyes are studied by using second-order Møller–Plesset perturbation theory (MP2) and time-dependent density functional theory(TDDFT) methods, respectively. It is found that the first excited state transition corresponds to charge transfer from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), and is responsible for molecular second-order nonlinear optical (NLO) properties. Our results reveal that the static first hyperpolarizability of hemicyanine derivatives has a linear relationship with the HOMO–LUMO energy gap. In addition, we also find the linear effect of charge transfer magnitude Δq on the first hyperpolarizability β. Our study may be helpful to further understand the structure–property relationship of the organic NLO materials.