Ground State Geometries Research Articles

A DFT study of a set of natural dyes for organic electronics.

We systematically investigate, at density functional theory level, the electronic properties of a set of ten carotenoid molecules with different conjugation length. Ground state geometries were fully optimized using both B3LYP and its long-range corrected version, i.e., the CAM-B3LYP functional. The time-dependent DFT approach (TD-DFT) was also performed for the calculation of the excited states of the optimized geometries and the results were compared to the experimental ones, when available. Our findings indicate a dependence of the transition vertical energies, oscillator strengths, and transition dipole moments on the extension of conjugation, as expected. We also investigate the impact of the intra-molecular vibrations on the absorption spectrum by means of the Franck-Condon (FC) and nuclear ensemble (NE) approach to spectra simulation. Our simulations suggest that the Franck-Condon approximation may not be suitable to appropriately characterize the vibronic progression of these molecules, whereas the NE approach provides a contribution that vary from negligible to meaningful depending on which molecule and energy region is under analysis.

Density functional theory study on the dihydrogen bond cooperativity in the growth behavior of dimethyl sulfoxide clusters

We have carried out a density functional theory study on the structures of DMSO clusters and analysed the structure and their stability using molecular electrostatic potential and quantum theory of atoms-in-molecules (QTAIM). The ground state geometry of the DMSO clusters, prefer to exist in ouroboros shape. Pair wise interaction energy calculation show the interaction between methyl groups of adjacent DMSO molecules and destabilization is created by the methyl groups which are away from each other. Molecular electrostatic potential analysis shows the existence of σ-hole on the odd numbered clusters, which helps in their highly directional growth. QTAIM analysis show the existence of two intermolecular hydrogen bonds, of type SO⋯HC hydrogen bonds and methyl CH⋯HC dihydrogen bonds. The computed ρ and Laplacian values were all positive for the intermolecular bonds, supporting the existence of noncovalent interactions. The computed ellipticity for the dihydrogen bonds have values>2, which confirms the delocalization of electron, are mainly due to the hydrogen-hydrogen interactions of methyl groups. A plot of total hydrogen bonding energy vs the observed total local electron density shows linearity with correlation coefficient of near unity, which indicates the cooperative effects of intermolecular dihydrogen H·H bonds.

Derivatives of 1-benzyl-4-(4-triphenylvinylphenyl) pyridinium bromide: Synthesis, characterization, mechanofluorochromism/aggregation-induced emission (AIE) character and theoretical simulations

4-(4-triphenylvinyl phenyl) pyridine (TPEPy) was used, along with the benzile bromide derivatives, to prepare 1-benzyl-4-(4-triphenylvinyl phenyl) pyridinium bromide (1) and its derivatives by replacing the benzyl bromide with 4-cyanobenzyl bromide for 2, 4-nitrobenzyl bromide for 3 and 4-trifluoromethyl benzyl bromide for 4, respectively. The maxima of the photoluminescent (PL) spectra of the freshly prepared powder samples of 1 ~ 4 are in the range of 510nm ~ 530nm with the absolute luminescence quantum yields (ALQY) of 88.10% for 1, 4.69% for 2, 1.70% for 3 and 36.30% for 4, respectively, which would redshift to the range of 554nm ~ 571nm with ALQYs of 54.70% for 1, 41.00% for 2, 14.70% for 3 and 43.40% for 4, respectively, after they are ground. At the same time, 1 ~ 4 have no obvious PL bands in dichlormethane solution (10-5mol/L) until ≥ 80% n-hexane was added. Finally, the ground-state geometries and the UV-Vis absorption spectra of 1 ~ 4 were simulated at B3LYP/6-31G(d,p) level to theoretically explain their photophysical behaviors.

Hyperfine structure of alkali-metal diatomic molecules

We present calculations of the hyperfine coupling constants for all the heteronuclear alkali-metal diatomic molecules at the equilibrium geometry of the electronic ground state. These constants are important in developing methods to control ultracold polar molecules. The results are based on electronic structure calculations using density functional theory, and are in good agreement with experiment for the limited set of molecules for which experiments are so far available.

A theoretical study on the geometry and spectroscopic properties of ground-state and local minima isomers of (CuS)n=2-6 clusters

Spectroscopic properties of gas-phase copper sulfide clusters (CuS)n (n = 2–6) are calculated using Density Functional Theory (DFT) and time-dependent (TD) DFT approaches. The energy landscape of the potential energy surface is explored through a basin-hopping DFT methodology. Ground-state and low-lying isomer structures are obtained. The global search was performed at the B3PW91/SDD level of theory. Normal modes are calculated to validate the existence of optimal cluster structures. Energetic properties are obtained for the ground-state and isomer clusters and their relative energies are evaluated for probing isomerization. This is a few tenths of an eV, except for (CuS)2 cluster, which presents energy differences of ∼1 eV. Notable differences in the infrared spectra exist between the ground-state and first isomer structures, even for the (CuS)5 cluster, which has in both configurations a core copper pyramid. TDDFT provides the simulated absorption spectrum, presenting a theoretical description of optical absorption bands in terms of electronic excitations in the UV and visible regions. Results exhibit a significant dependence of the calculated UV/vis spectra on clusters size and shape regarding the ground state structures. Optical absorption is strong in the UV region, and weak or forbidden in the visible region of the spectrum.

Structural and electronic study of iron-based dye sensitizers for solar cells using DFT/TDDFT.

Ruthenium-based molecules have proven their efficiency as photosensitizers in dye-sensitized solar cells. However, due to the high cost and scarcity of this noble metal, in this work we investigated the effects of replacing the ruthenium in photosensitizers with iron because it is less expensive and more abundant. DFT and TD-DFT methods were used to explore the resulting systems. The B3LYP functional was employed to compute the ground-state geometries and the frontier molecular orbitals for four complexes of general formula M(Rbpy)2S2N2C2 (M=Ru or Fe; R=COOH or COOEt). We also used TD-M06 to investigate the electronic properties and to simulate the absorption spectra of these Ru-based and Fe-based complexes. Finally, CPCM was applied to explore the effect of DMF solvent. The HOMOs of these Ru-based and Fe-based molecules were found to have metal d orbital and π(S2C2N2) orbital character, while their LUMOs had π*(R-bpy) orbital character. In addition, values of the light-harvesting efficiency (LHE), open circuit voltage (V oc), and driving force (∆G inject) were calculated for the Ru-based and Fe-based molecules. According to our results, the maximum absorbance, the LHE, V oc, and ∆G inject values for complexes 2 and 4 (Fe-based dyes) are very close to those of complexes 1 and 3 (Ru-based dyes). Thus, our studies indicate that the Ru in photosensitizers can be replaced with the much less expensive metal Fe, as the resulting Fe-based dyes appear to be promising candidates for use in solar cells.

Identifying the Ground State Geometry of a MoN2 Sheet through a Global Structure Search and Its Tunable p-Electron Half-Metallicity

MoN2 and MoS2 sheets are representatives of two-dimensional transition metal dinitrides and dichalcogenides, respectively. Their similarity in atomic ratios misled people to make an incorrect assumption in previous studies that the former adopts the geometry of the latter. However, compared with S, N is smaller and has fewer valence electrons, and N is more effective in mediating magnetic couplings; therefore, a different geometry and different properties can be expected for the MoN2 sheet. Here using a global structure search, for the first time we have identified the ground state geometry of this sheet named Tetra-MoN2 that is much more stable than the H phase proposed previously. Different from the metallic nature of H-MoN2, Tetra-MoN2 is a semiconductor having an indirect band gap of 1.41 eV with a flexible strain tunability. In particular, Tetra-MoN2 can exhibit rich half-metallic behaviors mediated by the polarized p electron of N and induced by low-concentration hole doping and small strains that are readily achievable experimentally.

Density functional theoretical studies on electronic structural, optical and oxidation properties of thioxylated peptides

Thioxylated peptide bond in simple dipeptides and tripeptides is found to amend the structural, optical and redox properties of the same relying on the position of substitution (N- and C-terminals). The electronic structural investigations show that the geometrical parameters are found to be highly influenced by the thioxo substitution at N-terminus. However, the absorbance properties are influenced by thioxo substitution at C-terminal, where blue shifts in π–π* transitions are observed compared to unsubstituted one. Similarly, the cationization reveals that the substitution at C-terminal promotes the conformational shift. Further, the computational studies clearly indicate that the N-terminal substitution effects the ground state geometry, while substitution at other position influences the excited and redox properties. The observed conformation switches in C-terminal conformers have been proposed as a candidate for redox switch, where the states (neutral and cation) were probed using computed vibrational data and chemical shift values.

Electron affinity of modified benzene

AbstractThe electron affinities of organic molecules obeying Hückel's rule of aromaticity are vanishingly small, if not negative. For example, benzene, a classic example of an aromatic molecule, has an electron affinity of −1.15 eV. Using density functional theory, we have systematically calculated the electron affinities and vertical detachment energies of C6H6 by substituting H with halogen (F) and superhalogen (BO2) moieties, as well as replacing one of the C atoms with B. The ground state geometries were obtained by examining about 330 isomers. The electron affinities are found to steadily increase with these substitutions/replacements, even surpassing that of Cl, the element with the highest electron affinity in the periodic table, in the case of C5BH(BO2)5. In some special cases such as C6H5(BO2) the electron affinity and vertical detachment energy differ by as much as 5 eV, indicating substantial changes in the geometry as the electron is removed from the anion. We hope that the ability to change the negative electron affinity of C6H6 to large positive values by substituting H and/or replacing C atom will motivate experimental studies.

Antimicrobial activities, DNA interactions, spectroscopic (FT-IR and UV-Vis) characterizations, and DFT calculations for pyridine-2-carboxylic acid and its derivates

In this paper, pyridine- 2- carboxylic acid, also known as picolinic acid (pic), and its two derivate, 4- methoxy-pyridine- 2- carboxylic acid (4-Mpic) and 4- chloro-pyridine- 2- carboxylic acid (4-Clpic) have been characterized by FT-IR and UV-Vis spectroscopy techniques as well as DFT calculations. B3LYP level of Density Functional Theory (DFT) method was used to obtain ground state geometries, vibration wavenumbers, first order hyperpolarizabilities and molecular electrostatic potential (MEP) surfaces for pic, 4Clpic and 4Mpic. The electronic absorption wavelengths and HOMO-LUMO energies were investigated by time dependent B3LYP (TD-B3LYP) level with the conductor-like polarizable continuum model (CPCM). The effects of Cl atom and OCH3 group on HOMO-LUMO energy gaps and first order hyperpolarizability parameters of pic, 4Clpic and 4Mpic molecules were examined. All molecules were screened for their antibacterial activities against Gram-positive and Gram-negative bacteria and for their antifungal activities against yeast strains by using minimal inhibitory concentration method (MIC). All compounds (pic, 4Mpic and 4Clpic) have been found to be very active against to the Gram (+) and Gram (−) bacteria. The DNA interactions of pic, 4Clpic and 4Mpic were analyzed by molecular docking simulations, and the interaction of the 4Mpic molecule with DNA is found to be higher than 4Clpic and pic.

Synthesis, characterization and spectroscopic studies of binuclear lanthanide complexes containing the anti-inflammatory drug Ibuprofen and CH3-disubstituted bipyridine ligands: Influence of methyl group position in the photoluminescence

The synthesis, solid state characterization, theoretical and experimental photoluminescence studies of two new important classes of binuclear lanthanide complexes: [Ln2(Ibf)6(4,4'-dmbpy)2] Eu = 1, Gd = 2 and Tb = 3) and [Ln2(Ibf)6(5,5'-dmbpy)2] Eu = 4, Gd = 5 and Tb = 6) (where: Ibf = non – steroidal anti – inflammatory drug (NSAID) Ibuprofen, 4,4'-dmbpy and 5,5'-dmbpy are 4,4'-dimethyl-2,2'-bipyridine and 5,5'-dimethyl-2,2'-bipyridine, respectively) are reported in this work. The analytical and spectroscopic data suggest the formation of binuclear compounds. The RM1 model was used to obtain the molecular structures of the EuIII complexes and its optimized ground state geometries were used to calculated all details involved in the energy transfer process and compared with experimental data, being in an optimal agreement. The lowest ligand triplet state (T1) in these systems were obtained through of the time – resolved phosphorescence spectra, proving that the intramolecular energy transfer is responsible by high photoluminescence in these compounds. Still, the values of energy of the centroid of the 5D0 → 7F0 transition for the EuIII complexes, indicate an increase in the covalence degree for the Eu – L bonds, which is due to inductive effect (+I) of the –CH3 groups in the ancillary ligands, when compared with those [Eu2(Ibf)6(bpy)2] recently published. The high values of quantum efficiency and solubility in common organic solvents can opens the possibility to test this binuclear compounds in the field of efficient luminescent devices and biomarkers.

Synthesis, Structural Characterization and Biological Evaluation of Rhenium(I) Tricarbonyl Complexes with β‐Carboline Ligands.

AbstractTwo β‐carboline rhenium(I) complexes, fac‐[Re(CO)3(dppz)(nHo)]O3SCF3 and fac‐[Re(CO)3(nHo)2Cl] where dppz=dipyrido[3, 2‐a:2′,3′‐c] phenazine and nHo=9H‐pyrido[3, 4‐b]indole (norharmane), have been synthesized. These complexes were fully characterized by structural X‐ray diffraction, 1H and 13C NMR, UV‐vis absorption and FT‐IR spectroscopy and mass spectrometry. Ground state geometry optimization was carried out in vacuo with the PBE0 hybrid functional using the LanL2DZ basis set. The characterization was complemented with TD‐DFT calculations using several hybrid functionals. Cellular uptake and cytotoxic effect of both complexes against human lung carcinoma (A549) cells were evaluated. For comparative purpose, two related fac‐[Re(CO)3(L)(nHo)]+ complexes (L=bpy and phen) were included in the biological studies. The anti‐proliferative effect of the compounds was rationalized in terms of the different extension of the ligands π‐system.

Tuning of optoelectronic and charge transport properties in star shaped anthracenothiophene-pyrimidine derivatives as multifunctional materials

With the aim to tune the optoelectronic, charge transport and nonlinear optical properties, four novel star shaped compounds were designed from the initial structure 4,6-di(anthracenothiophen-2-yl)pyrimidine (DATP). The (2,5-di-(thiophen-2-yl)-4,6-di-(anthracenothiophen-2-yl)pyrimidine) (1), (2,5-di(benzo-thiophen-2-yl)-4,6-di-(anthracenothiophen-2-yl)pyrimidine) (2), 2,5-di(naphthothiophen-2-yl)-4,6-di-(anthracene-thiophen-2-yl)-pyrimidine (3), and 2,4,5,6-tetrakis(anthracene-thiophen-2-yl)pyrimidine (4) were deliberated by substituting the thiophene, benzothiophene, naphthothiophene and anthracenothiophene moieties at positions 2 and 5 of the pyrimidine unit in DATP, respectively. The ground and excited state geometries were optimized by adopting the density functional theory (DFT) and time-dependent DFT at B3LYP/6-31G** and TD-B3LYP/6-31G** level of theories, respectively. We shed light on the energies of the frontier molecular orbitals (FMOs), energy gaps (Egaps), absorption, fluorescence, total/partial density of states (T/PDOS), molecular electrostatic potentials (MEP) and non-linear optical (NLO) properties. The comprehensible intra-molecular charge transport has been noticed from side wings to the electron-deficient central core at both the ground and excited states. The increment in the wings length increases the electron affinity, reduces the ionization potential and lowered the hole reorganization energy. The higher electron affinity and smaller hole reorganization energy values revealed that newly designed materials might be thermodynamically more stable with enhanced intrinsic hole mobility.

Proton Induced Modulation of ICT and PET Processes in an Imidazo-phenanthroline Based BODIPY Fluorophores.

BODIPY fluorophores linked with an imidazo-phenanthroline donor at α and β positions have been synthesized. Intriguing intramolecular charge transfer phenomenon is observed in both the dyes which has been extensively investigated using UV-vis absorption, steady-state and time-resolved fluorescence measurements. H-bonding and intrinsic polarity of the solvents has modulated the absorption and emission bands of these fluorophores strongly causing significant increase in the Stokes shifts. In spite of having difference only in terms of the position of donor subunit, the photophysics of these dyes are not only significantly different from each other, but contradictory too. Interestingly, acidochromic studies revealed the shuttling mechanism between ICT and PET processes for BDP 2. Quantum chemical calculations have been employed further to support experimental findings. DFT and TD-DFT method of analysis have been used to optimize ground and excited state geometries of the synthesized dyes.

A combined experimental and computational investigation of solvatochromism of nonpolar laser dyes: Evaluation of ground and singlet excited-state dipole moments

In the present work, the solvatochromism of two large nonpolar laser dyes Exalite 384 (E384) and Exalite 416 (E416) has been studied both experimentally and computationally. The steady state absorption and fluorescence spectra have been measured in a series of polar protic, polar aprotic and non-polar/weakly polar solvents to investigate their solvatochromism and determine dipole moments. Various solvent correlation techniques, like Lippert–Mataga, Bilot–Kawski, Kawski–Chamma–Viallet, Bakhshiev and Reichardt methods were used to evaluate the singlet excited and ground state dipole moments. Kamlet–Taft and Catalan solvent parameters were used by means of multiple linear regression (MLR) method to analyze specific and non-specific solute-solvent interactions. Computational studies were carried out to optimize ground and excited state geometries using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, in vacuum. This study also extends to evaluate the electronic transition energies from ground to first electronic excited state of solvated laser dyes employing semiempirical wave function model. In particular, the semiempirical method ZINDO has been combined with integral equation formalism of polarizable continuum model (IEF-PCM) to calculate solute-solvent interaction potential which is comparatively studied with ET(30) polarity scale along with experimental. The intramolecular charge transfer and hybridization is demonstrated by natural bond orbital analysis (NBO). The ground (μg) and excited state dipole moments (μe) of these dyes computed and those determined experimentally are compared and the results are discussed.

Theoretical S1 ← S0 Absorption Energies of the Anionic Forms of Oxyluciferin by Variational Monte Carlo and Many-Body Green's Function Theory.

The structures of three negatively charged forms (anionic keto-1 and enol-1 and dianionic enol-2) of oxyluciferin (OxyLuc), which are the most probable emitters responsible for the firefly bioluminescence, have been fully relaxed at the variational Monte Carlo (VMC) level. Absorption energies of the S1 ← S0 vertical transition have been computed using different levels of theory, such as TDDFT, CC2, and many-body Green's function theory (MBGFT). The use of MBGFT, by means of the Bethe-Salpeter (BS) formalism, on VMC structures provides results in excellent agreement with the value (2.26(8) eV) obtained by action spectroscopy experiments for the keto-1 form (2.32 eV). To unravel the role of the quality of the optimized ground-state geometry, BS excitation energies have also been computed on CASSCF geometries, inducing a non-negligible blue shift (0.08 and 0.07 eV for keto-1 and enol-1 forms, respectively) with respect to the VMC ones. Structural effects have been analyzed in terms of over- or undercorrelation along the conjugated bonds of OxyLuc by using different methods for the ground-state optimization. The relative stability of the S1 state for the keto-1 and enol-1 forms depends on the method chosen for the excited-state calculation, thus representing a fundamental caveat for any theoretical study on these systems. Finally, Kohn-Sham HOMO and LUMO orbitals of enol-2 are (nearly) bound only when the dianion is embedded into a solvent (water and toluene in the present work); excited-state calculations are therefore meaningful only in the presence of a dielectric medium which localizes the electronic density. The combination of VMC for the ground-state geometry and BS formalism for the absorption spectra clearly outperforms standard TDDFT and quantum chemistry approaches.

A first principles study of key electronic, optical, second and third order nonlinear optical properties of 3-(4-chlorophenyl)-1-(pyridin-3-yl) prop-2-en-1-one: a novel D- $$\pi $$ π -A type chalcone derivative

In this work we assess the significant electrooptic properties of a novel chalcone derivative 3-(4-chlorophenyl)-1-(pyridin-3-yl) prop-2-en-1-one using a computational approach. The ground-state molecular geometry was optimized, and geometrical parameters and vibrational modes are established and found to be in strong correlation with experimental results. The excitation energy is observed to be 326 nm (3.8 eV), calculated at the TD/B3LYP/6-31G level (stands for time dependent/Becke’s three Lee-Yang-Parr/basis set). Additionally, a unique insight was gained on a number of properties of the molecular levels such as the HOMO-LUMO gap (i.e. $${\sim } 4\,\hbox {eV}$$ ) and electrostatic potential maps. The potential applications of the 3-(4-chlorophenyl)-1-(pyridin-3-yl)prop-2-en-1-one (CPP) molecule in nonlinear optics are confirmed by second and third harmonic generation studies at five different characteristic wavelengths. The static and dynamic polarizability are found to be many-fold higher than that of urea. The second and third harmonic generation values of the titled molecule are found to be 56 and 158 times higher than standard urea molecule, respectively, computed at same wavelength (i.e. 1064.13 nm). From these studies it is clear that the material possesses superior properties and could be applied in optoelectronic device fabrications.

Exploring the charge transfer nature and electro-optical properties of anthracene based sensitizers @TiO 2 cluster

Abstract Two new anthracene derivatives donor–π–acceptor (Compound 1) and acceptor–π–acceptor (Compound 2) have been designed with the aim to understand the effect of donor and acceptor on the electronic, optical and charge transfer properties of sensitizers and sensitizers@TiO2 cluster. The electron donating group (–OH) and acceptor (–COOH) have been substituted at periphery and the effect was studied thoroughly. The ground state geometries of both the compounds were optimized by using density functional theory (DFT) at B3LYP/6-31G**, CAM-B3LYP/6-31G** LC-BLYP/6-31G**, BHandHLYP/6-31G** and PBE1PBE/6-31G** levels of theory. Moreover, ground state geometries of sensitizers@TiO2 cluster were optimized by adopting the same methods along with LANL2DZ pseudopotential for Ti while 6-31G** basis set for all other atoms. The electro-optical properties and charge transfer nature of dye adsorbed at TiO2 cluster were also systematically investigated. The absorption spectra of anthracene derivatives before and after adsorption at TiO2 cluster were limelighted by adopting time dependent DFT.

Surface-enhanced Raman scattering of dipolar molecules by the graphene Fermi surface modulation with different dipole moments

We report the modulation of Raman scattering spectrum of chromophore/graphene hybrids by tunning the molecular polarization with different terminal groups (methyl, methoxy, nitrile, and two nitros). Based on the density functional theory, the specific dipole moment values of the chromophore molecules are calculated. An obvious surface-enhanced Raman scattering (SERS) was observed and the scattering intensity of molecule increases with enlarged dipole moment. According to the analysis of G band Raman shifts of graphene, the enhancement of the Raman signal can be attributed to strong electronic coupling between graphene and chromophore, which is closely related with the modulation of graphene Fermi surface by changing the dipole moment of the molecule. Besides, the optimization of the ground state geometry and the binding energy of the hybrids were also calculated with the Density Functional Based Tight Bonding (DFTB) method, which confirms that the enhanced Raman scattering of molecules on graphene arises from the improved energy level matching between graphene Fermi surface and molecular band, further providing a new way to design novel SERS devices.

DFT Study of Electronic and Optical Properties of Small Oligothiophenes Based on Terthiophene End-capped by Several Donor Groups

Eight small molecules based on terthiophene end-capped by several donor groups have been carried out using density functional theory (DFT) and time-dependent (TDDFT) methods in neutral and doped states. The theoretical ground-state geometry, electronic structure and optical properties of the studied molecules were obtained by the DFT and TD-DFT methods at the B3LYP level with 6-31G(d) basis set. Theoretical knowledge of the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels the gap energy (Eg) and the open-circuit voltage (Voc) of the studied compounds are calculated and discussed. The effects of the donor group substituents on the geometries and optoelectronic properties of these materials are discussed to investigate the relationship between molecular structure and optoelectronic properties. The results of this work suggest some of these materials as a good candidate for organic solar cells. DOI: http://dx.doi.org/10.17807/orbital.v9i3.995