Frontier Molecular Orbital Energy Gap Research Articles

Theoretical Study on Energetic Derivatives Based on 3,7‐Bis(Alkenyl)‐2,4,6,8‐Tetraazabicyclo[3.3.0]Octane

AbstractDensity functional theory at B3LYP/6‐311G (d,p) level was employed to investigate the physicochemical properties of the 3,7‐bis(alkenyl)‐2,4,6,8‐tetraazabicyclo[3.3.0]octane based energetic materials. Their frontier molecular orbital energy gaps, heats of formation, detonation properties and thermal stabilities were calculated. The results show that the frontier molecular orbital energy gaps were from 3.56 eV (A2) to 5.43 eV (C3); the heats of formation were from −154.8 (A5) to 3007.2 kJ mol−1 (C2); the detonation velocities were from 5.22 (A1) to 8.90 km s−1 (A5) while the detonation pressures were from 10.8 (A1) to 36.4 GPa (A5). In view of the bond dissociation energies, the data were found to be from 8.9 (A4) to 321.8 kJ mol−1 (A1). Take both of detonation properties and bond dissociation energies into consideration, compounds A5 and C5 were finally selected as candidates for high energy density materials since they have excellent detonation properties and acceptable thermal stabilities.

Synthesis, crystal structure, Hirshfeld surface analysis and HOMO–LUMO energy levels of (E)-N′-(naphthalen-1-ylmethylene)-4-nitrobenzohydrazide

Abstract The title Schiff base compound (E)-N′-(naphthalen-1-ylmethylene)-4-nitrobenzohydrazide crystal was grown by a slow evaporation method. The title compound was characterized by single crystal X-ray diffraction, Hirshfeld surface analysis, and Frontier molecular orbital analysis. The crystal belongs to the monoclinic system with P21/c space group. The crystal structure is stabilized by C H⋯O hydrogen bonding interaction and π π stacking interaction. The intermolecular interactions of the crystal structure were analyzed using Hirshfeld surface and fingerprint analysis. The frontier molecular orbital energy gap discloses charge transfer interaction involving donor and acceptor groups.

Crystal growth, Hirshfeld surface analysis, DFT study and third order NLO studies of thiourea 4 dimethyl aminobenzaldehyde

In this work we investigate the crystal growth and the characterization of Thiourea 4 dimethyl aminobenzaldehyde (TDA) crystal. The Molecular geometry shows good agreement with Experimental and Theoretical (HF and DFT) bond lengths and bond angles. From X-ray diffraction studies it shows that the structure belongs to monoclinic structure and experimental, refinement data also discussed. Hirshfeld surface analysis used to clarify the intermolecular interactions in a visual manner. Vibrational assignments of TDA crystal is discussed by FT-IR and FT-Raman spectroscopic studies. The assignments are compared with Density Functional Theory calculation and it shows good agreement with experimental data. The Frontier molecular orbital energy gap is found by TD-DFT method with HOMO-LUMO calculation. The Third order NLO studies for TDA organic crystal is done by Z-scan technique and Optical parameters like Non linear and Linear refractive index are calculated.

Deciphering the Ethylene Carbonate-Propylene Carbonate Mystery in Li-Ion Batteries.

As one of the landmark technologies, Li-ion batteries (LIBs) have reshaped our life in the 21stcentury, but molecular-level understanding about the mechanism underneath this young chemistry is still insufficient. Despite their deceptively simple appearances with just three active components (cathode and anode separated by electrolyte), the actual processes in LIBs involve complexities at all length-scales, from Li+ migration within electrode lattices or across crystalline boundaries and interfaces to the Li+ accommodation and dislocation at potentials far away from the thermodynamic equilibria of electrolytes. Among all, the interphases situated between electrodes and electrolytes remain the most elusive component in LIBs. Interphases form because no electrolyte component (salt anion, solvent molecules) could remain thermodynamically stable at the extreme potentials where electrodes in modern LIBs operate, and their chemical ingredients come from the sacrificial decompositions of electrolyte components. The presence of an interphase on electrodes ensures reversibility of Li+ intercalation chemistry in anode and cathode at extreme potentials and defines the cycle life, power and energy densities, and even safety of the eventual LIBs device. Despite such importance and numerous investigations dedicated in the past two decades, we still cannot explain why, nor predict whether, certain electrolyte solvents can form a protective interphase to support the reversible Li+ intercalation chemistries while others destroy the electrode structure. The most representative example is the long-standing "EC-PC Disparity" and the two interphasial extremities induced therefrom: differing by only one methyl substituent, ethylene carbonate (EC) forms almost ideal interphases on the graphitic anode, thus becoming the indispensable solvent in all LIBs manufactured today, while propylene carbonate (PC) does not form any protective interphase, leading to catastrophic exfoliation of the graphitic structure. With one after another hypotheses proposed but none satisfactorily rationalizing this disparity on the molecular level, this mystery has been puzzling the battery and electrochemistry community for decades. In this Account, we attempted to decipher this mystery by reviewing the key factors that govern the interaction between the graphitic structure and the solvated Li+ right before interphase formation. Combining DFT calculation and experiments, we identified the partial desolvation of the solvated Li+ at graphite edge sites as a critical step, in which the competitive solvation of Li+ by anion and solvent molecules dictates whether an electrolyte is destined to form a protective interphase. Applying this model to the knowledge of relative Li+ solvation energy and frontier molecular orbital energy gap, it becomes theoretically possible now to predict whether a new solvent or anion would form a complex with Li+ leading to desirable interphases. Such molecular-level understanding of interphasial processes provides guiding principles to the effort of tailor-designing new electrolyte systems for more aggressive battery chemistries beyond Li-ion.

Synthesis, Characterization and DFT Studies of Two Zinc(II) Complexes Based on 2-Isopropylimidazole

Two novel coordination compounds, [Zn(L)2(OOCH)2] (1) and [Zn(L)3(OCHO)](OCHO)]·H2O (2) (where L = 2-isopropylimidazole, C6H10N2) have been prepared by reaction of 2-isopropylimidazole with zinc(II) formate at room temperature using toluene as solvent. These compounds were characterized by elemental and thermal analyses, IR, 1HNMR and 13CNMR spectroscopies, single crystal X-ray diffraction and DFT studies. The Zn centers in 1 and 2 adopt pseudo-tetrahedral coordination geometries. Compound 1 crystallizes in the monoclinic system P2/c space group whereas compound 2 crystallizes in the P-1 space group of the triclinic crystal system. Several types of hydrogen intra-/intermolecular interactions are observed in these materials and extend into a two-dimensional leaf like network in 1 and a two-dimensional lattice of rectilinear pillars in 2. Compounds 1 and 2 were also optimized and their frontier molecular orbitals, global reactivity descriptors, molecular electrostatic potential, natural bond orbitals were investigated using density functional theory (DFT). In fact the induced structural differences from complex 1 to complex 2 led to the reduction of the frontier molecular orbital energy gap by 1.338 eV and a decrease of the chemical hardness by 0.669 eV.

Design of acceptors with high mobility via substitutions on dimeric perylene diimide for organic solar cells: A theoretical study

Abstract The aim of this work is to provide an in-depth study of the optical, electronic, and charge transfer properties for substituent effects on the dimeric perylene diimide (PPDI). The ground state geometry and relevant electronic properties of investigated molecules for photovoltaic applications were evaluated by the CAM-B3LYP/6–31G (d,p) method. The absorption spectra simulated at the TD-B3LYP/6–31 + G (d,p) level. The results reveal that different positions and amount of substituents significantly affect on the distributions of frontier molecular orbitals for PPDI. The different positions of the same substituent group affect the frontier molecular orbital energy and energy gap of PPDI slightly. The different positions and amount of substituents affect the absorption spectra of PPDI slightly. The calculated reorganization energies of electrons and holes for PPDI and its derivatives implied that their charge transfer rates are higher than that of the typical electron and hole transport materials, respectively. Moreover, we have also predicted the mobility of designed molecules with better performances.

Synthesis, crystal structure, Hirshfeld surface analysis and frontier molecular orbital analysis of 2-((2-hydroxynaphthalen-1-yl)methylene)hydrazinecarbothioamide

Abstract The title compound 2-((2-hydroxynaphthalen-1-yl)methylene)hydrazine-carbothioamide was grown by slow evaporation method. The compound was characterized by single crystal X-ray diffraction, Hirshfeld surface analysis and frontier molecular orbital analysis. The crystal belongs to monoclinic system with P21/c space group. The crystal structure is stabilized by N−H···S, N−H···N, and O−H···N hydrogen bonding interactions. The intermolecular interactions of the crystal structure were analyzed using Hirshfeld surface and fingerprint analysis. The frontier molecular orbital energy gap discloses charge transfer interaction involving donor and acceptor groups.

Synthesis, optical, experimental and theoretical investigation of third order nonlinear optical properties of 8-hydroxyquinolinium 2-carboxy-6-nitrophthalate monohydrate single crystal

Single crystals of 8-hydroxyquinolinium 2-carboxy-6-nitrophthalate monohydrate (8HQNP) were obtained from slow evaporation solution growth method using methanol-water (1:1) as a solvent. Powder X-ray diffraction was utilized to compute the unit cell parameters and dislocation density of 8HQNP crystal. The crystalline perfection of the as-grown crystal was investigated by high-resolution X-ray diffraction at room temperature. The molecular structure was analyzed by identifying the functional groups from FT-IR and FT-Raman spectra. The cut-off wavelength and the corresponding optical band gap obtained from an optical spectrum were 376 nm and 3.29 eV respectively. The dispersion nature of refractive index was investigated by the single-oscillator Wemple and Di-Domenico model. Red emission was observed in the photoluminescence spectrum when excited with 376 nm. The low birefringence and high laser damage threshold (8.538 GW/cm2) values dictate the suitability of the crystal for optical devices. Z-scan studies revealed the third order nonlinear absorption coefficient (β) and refractive index (n2) of the 8HQNP crystal. The theoretical value of third order nonlinear susceptibility obtained from density function theory is good accordance with the experimental value. The frontier molecular orbital energy gap decreases with increasing external electric field in different directions which attributed to the enhancement of the second hyperpolarizability. The grown title crystal is thermally stable up to 102 °C which was identified using thermal analysis. Mechanical strength of 8HQNP was estimated by using Vicker's microhardness studies.

Theoretical study on the spectroscopic and third-order nonlinear optical properties of two-dimensional charge-transfer pyrazine derivatives

ABSTRACTIn this paper, density functional theory method was employed to study the electronic absorption spectrum and electronic static second hyperpolarisability of X-shaped pyrazine derivatives with two-dimensional charge-transfer structures. Computational results show that the push–pull electron abilities of the substituent groups and the length of the conjugated chains affect the electronic spectrum and static second hyperpolarisability of the pyrazine derivatives. As the push–pull electron abilities of the substituent groups or the length of the conjugated chains increases, the frontier molecular orbital energy gap decreases, resulting in increased second hyperpolarisability and redshift of the electronic absorption bands. The electronic absorption spectra of the pyrazine derivatives maintain good transparency in the blue light band. The electronic static second hyperpolarisability exhibits a linear relationship to the frontier molecular orbital energy gap. Particularly, increasing/decreasing the push–pull electron abilities of the substituent groups considerably affect the static second hyperpolarisability in long conjugated systems, which is important to the modulation of molecular organic nonlinear optical (NLO) properties. The studied pyrazine derivatives show large third-order NLO response and good transparency in the blue light band and are thus promising candidates as NLO materials for photonics applications.

STRUCTURAL, ELECTRONIC AND VIBRATIONAL STUDY OF 4, 6-DICHLORO-5-METHYLPYRIMIDINE: A DFT APPROACH

Molecular structure, molecular electrostatic potential (MEP) and theoretical vibrational spectra of 4, 6-dichloro-5-methylpyrimidine (DMP) molecule have been presented in this paper. The vibrational spectra were calculated for monomer, dimer and unit cell DMP molecule using density function theory (DFT) and ab initio Hartree-Fock (HF) (for monomer) method employing 6-311++G (d, p) basis set using Gaussian 09 program. The frequencies obtained by DFT have smaller values than obtained from HF due to the inclusion of electron correlation in the previous one. Electronic absorption calculations are performed both in the gas and solvent phase using TD-DFT (including IEF-PCM model) to understand the stability, charge transfer and frontier molecular orbital energy gap. Large value of energy gap leads to the stability of molecule. Overlapping between calculated and the experimental structure show that the optimized geometry reproduced exactly similar structure as by the experiment.Journal of Institute of Science and TechnologyVolume 22, Issue 1, July 2017, Page: 51-60

Size-, electric-field-, and frequency-dependent third-order nonlinear optical properties of hydrogenated silicon nanoclusters.

We investigated the electronic properties and second hyperpolarizabilities of hydrogenated silicon nanoclusters (H-SiNCs) by using the density functional theory method. The effects of cluster size, external electric field and incident frequency on the second hyperpolarizability were also examined, respectively. We found that small H-SiNCs exhibit large second hyperpolarizability. With the increase of the number of silicon atoms in H-SiNCs, the frontier molecular orbital energy gap decreases, attributed to the enhancement of the second hyperpolarizability. Interestingly, we also found the electric-field-induced gigantic enhancement of the second hyperpolarizability for H-SiNCs due to the change of electron density distributions. In addition, our results demonstrate a significant dependence on the frequency of incident light.

Efficiency of fluorinated alcohol for extraction of organic acid from its dilute aqueous solution: A molecular optimization study of extractant

Abstract The quantum chemical parameters of fluorinated octanol, such as charge distribution, molecular electrostatic potential and frontier molecular orbital have been investigated through quantum chemistry calculation by DFT method using the B3LYP level with the standard 6-311++G(d,p) basis set. In first step the natural population analysis (NPA) and molecular electrostatic potential (MEP) methods were applied to determine the reactive site of fluorinated octanol. In second step comparative analysis of frontier molecular orbital energy gaps of fluorinated octanol and benzoic acid was used to investigate the effect of fluorinated substitutional degree on benzoic acid extraction behavior of fluorinated octanol. The calculated results suggested that the reactive site is localized on the oxygen atom and the electron donor strength of the oxygen atom decreases with the increase of the fluorinated substitional degree due to the electron-withdrawing of fluorous group. 1 H ,1 H ,2 H ,2 H -perfluoro-1-octanol and 5,5,6,6,7,7,8,8-nonafluoro-1-octanol were selected as the extractants to testify the proposed theory. According to the prediction, the extraction capability on benzoic acid by 1 H ,1 H ,2 H ,2 H -perfluoro-1-octanol is lower than that of 5,5,6,6,7,7,8,8-nonafluoro-1-octanol at room temperature. The experimental results are in agreement with the corresponding theoretical data.

Organic Light Emitting Properties of the Functional Pyridine-Containing Diacylhydrazones

The pyridine-containing diacylhydrazones derivatives are functional organic light emitting molecular materials. In this paper, The S0 ground states and the S1 excited states of the four pyridine-containing diacylhydrazones compounds were optimized with density functional theory (DFT) at B3LYP/3-21+G level and single-excitation configuration interaction at CIS/3-21+G method, respectively. We discussed in detail the relationships between the molecular orbital energy, absorption and emission performances and the structures of the four compounds. In addition, the analysis on frontier molecular orbital (FMO) energy gaps indicated that the stronger the conjugations are, the much more red-shift of the absorption spectrum will be. According to the calculated absorption and emission spectra data, it can be conclude that four pyridine-containing diacylhydrazones compounds are one of the alternative electron transporting and photoactive materials.

Spectroscopic Aspects, Structural Elucidation, Vibrational and Electronic Investigations of 2-Methoxy-1,3-Dioxolane: An Interpretation Based on DFT and QTAIM Approach

Extensive vibrational spectroscopic investigations along with theoretical quantum chemical studies on 2-methoxy-1,3-dioxolane (MDOL) have been consummated. The experimentally observed spectral data (FT-IR and FT-Raman) of the title compound were compared with the spectral data obtained by DFT/B3LYP method. The 1H and 13C nuclear magnetic resonance (NMR) spectra were simulated by using the gauge independent atomic orbital (GIAO) method and the absolute chemical shifts related to TMS were compared with experimental spectra. The theoretical UV-Visible spectrum of the title compound was measured in different solvent and the electronic properties, such as excitation energies, oscillator strength and wavelengths were performed by time-dependent density functional theory (TD-DFT) approach. The kinetic stability of the molecule has been determined from the frontier molecular orbital (FMO) energy gap. Total density of state (TDOS) and partial density of state (PDOS) of the MDOL in terms of Mulliken population analysis Topological parameters at bond critical point have been analyzed in MDOL by Bader’s were calculated and analyzed. Reduced density gradient (RDG) of the MDOL was given to investigate interactions of the molecule. ‘Atoms in molecules’ (AIM) theory in detail. In addition, the temperature dependence thermodynamic properties and magnetic susceptibility of MDOL were calculated with the help of DFT/ B3LYP method using 6-311++G(d,p) basis set.

Investigations on stabilities and intermolecular interactions of different naphthalene derivatives dimers by using B3LYP and M06-2X density functional calculations

In this paper, the stabilities and hydrogen bond interactions of 4-chloro-1-naphthol, 1-hydrox-ynaphthalene and 1,4-dihydroxynaphthalene dimers have been theoretically investigated by means of study on binding energies with nonlocal hybrid three-parameter Lee-Yang-Parr, B3LYP, and M06-class functional calculations. Calculations on dimers aim to provide as a test of the efficacy of M06 calculations for intermolecular interaction calculations and more strongly bound systems. For hydroxyl- and halo-substituted derivatives of naphthalene, total electronic energies, their correction for the zero point vibrational energies with some calculated thermodynamic properties and their relative differences are together in order to discuss the rotamer structures. Static (hyper) polarizabilities and the electric dipole moments, frontier molecular orbital energy gaps and the relationships between them have been interpreted. Generally, they are seen that the calculated geometric parameters and spectral results were in a good agreement with the corresponding experimental data.

Unveiling photophysical properties of cyclometalated iridium(iii) complexes with azadipyrromethene and dipyrromethene ancillary: a theoretical perspective

A density functional theory/time-depended density functional theory was used to investigate a series of heteroleptic Ir(III) complexes (1–4) employing azadipyrromethene and closely related dipyrromethene derivatives as N^N ancillary ligands, in an effort to explore the underlying reasons of non-radiative behaviour of 1 and further adjust the photophysical properties by the modification of N^N ancillary ligands. The results reveal that the non-emissive phenomenon of 1 can be attributed to the weak 3ILCT character of the emissive excited state and large structure distortion, as well as the small Topt1–Sopt0 energy gap. Upon tailoring the N^N ancillary ligands, the geometry distortion of 2–4 becomes obviously smaller in comparison with 1, accordingly, the spectrum properties are also markedly affected. For instance, the enlargement of frontier molecular orbital energy gaps from 1 to 4 results in the blue-shift of their absorption and emission spectra, which is considered to be dominated by the ancillary ligand, while there is a little contribution from the Ir(III) center. Importantly, further analysis on the quantum yield (ΦPL) of these complexes also indicates a vital role of N^N ancillary ligands. It is intriguing to note that the designed complex 4 without pendant phenyl rings substituent in the ancillary ligand, possesses an efficient indirect spin-orbital coupling route, larger transition electric dipole moment (μS3), higher Topt1–Sopt0 energy gap and smaller S3–T1 splitting energy (ΔE(S3–T1)), which ensure its higher ΦPL compared to other complexes.

Theoretical characterization and design of highly efficient iridium (III) complexes bearing guanidinate ancillary ligand

A density functional theory/time-depended density functional theory was used to investigate the synthesized guanidinate-based iridium(III) complex [(ppy)2Ir{(NiPr)2C(NPh2)}] (1) and two designed derivatives (2 and 3) to determine the influences of different cyclometalated ligands on photophysical properties. Except the conventional discussions on geometric relaxations, absorption and emission properties, many relevant parameters, including spin-orbital coupling (SOC) matrix elements, zero-field-splitting parameters, radiative rate constants (kr) and so on were quantitatively evaluated. The results reveal that the replacement of the pyridine ring in the 2-phenylpyridine ligand with different diazole rings cannot only enlarge the frontier molecular orbital energy gaps, resulting in a blue-shift of the absorption spectra for 2 and 3, but also enhance the absorption intensity of 3 in the lower-energy region. Furthermore, it is intriguing to note that the photoluminescence quantum efficiency (ΦPL) of 3 is significantly higher than that of 1. This can be explained by its large SOC value<T1|HSO|Sn>(n=3–4) and large transition electric dipole moment (μS3), which could significantly contribute to a larger kr. Besides, compared with 1, the higher emitting energy (ET1) and smaller <S0|HSO|T1>2 value for 3 may lead to a smaller non-radiative decay rate. Additionally, the detailed results also indicate that compared to 1 with pyridine ring, 3 with imidazole ring performs a better hole injection ability. Therefore, the designed complex 3 can be expected as a promising candidate for highly efficient guanidinate-based phosphorescence emitter for OLEDs applications.

Systematic Study and Imaging Application of Aggregation-Induced Emission of Ester-Isophorone Derivatives

The dicyanoisophorone derivatives show obvious AIE behaviors in our previous work. To study the bioimaging application of these chromophores with AIE/AIEE properties, the ester groups substituted for one cyan to form a new family based on isophorone (2a–2e). 2a–2d exhibit obvious AIE/AIEE phenomena, while 2e shows fluorescence quenching in the aggregate state. The morphology and size of aggregates with different water contents were investigated using SEM and DLS, indicating that a large number of smaller globular or quadrate nanoparticles with average diameters in the range 78.79–392.7 nm in mixed solutions are related to these AIE/AIEE or ACQ behaviors. We also made comparative analyses of their optical properties in different states. The crystal data of 2a–2d reveal that the multiple intra- and intermolecular interactions leads to the molecular conformation being more stable, increases the planarity of compounds, restricts the intramolecular motions, and promotes the formation of J-type aggregate, enabling chromophores 2a–2d to emit intensely in the solid state. In addition, the frontier molecular orbital energy and band gap calculated by density functional theory are quite consistent with the experimental results. Finally, these AIE/AIEE-active compounds could be used in bioimaging applications, which immensely provide a new strategy to the application of some AIE/AIEE systems.

DFT simulation, quantum chemical electronic structure, spectroscopic and structure–activity investigations of 2-benzothiazole acetonitrile

The Fourier transform infrared and FT-Raman spectra of 2-benzothiazole acetonitrile (BTAN) have been recorded in the range 4000–450 and 4000–100cm−1 respectively. The conformational analysis of the compound has been carried out to obtain the stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers derived theoretically by B3LYP gradient calculations employing the standard 6-31G**, high level 6-311++G** and cc-pVTZ basis sets. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The 1H (400MHz; CDCl3) and 13C (100MHz;CDCl3) nuclear magnetic resonance (NMR) spectra are also recorded. The electronic properties, the energies of the highest occupied and lowest unoccupied molecular orbitals are measured by DFT approach. The kinetic stability of the molecule has been determined from the frontier molecular orbital energy gap. The charges of the atoms and the structure–chemical reactivity relations of the compound are determined by its chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods. The non-linear optical properties of the compound have been discussed by measuring the polarisability and hyperpolarisability tensors.

Characterization and density functional theory study of the antioxidant activity of quercetin and its sugar-containing analogues

Inhibition of free radicals using quercetin, hyperin and rutin is examined to determine their antioxidant effects and the structure–activity relationships of flavonoids. Two species of the free radicals are used, including hydroxyl radical (·OH) and superoxide anion radical (O2 −·). Density functional theory calculations under the level of B3LYP/6-311G (d) have been utilized to explore the structure, molecular properties and antioxidant abilities of the three flavonoids. Bond dissociation enthalpy (BDE) and frontier molecular orbital energy gap are investigated. They are compared with the experiment results assayed by the spectrophotometric. All of the flavonoids show a high activity on inhibiting ·OH and O2 −· radicals. Scavenging activity determined by half maximal inhibitory concentration (IC50) values of the three flavonoids decreases in the order: quercetin > hyperin > rutin. The calculations show that quercetin owns the lowest BDE values, which agree well with the experimental results of antioxidant activity determined by IC50 values.