Comparative study on electronic structures and optical properties of indoline and triphenylamine dye sensitizers for solar cells

The computations of the geometries, electronic structures, dipole moments and polarizabilities for indoline and triphenylamine (TPA) based dye sensitizers, including D102, D131, D149, D205, TPAR1, TPAR2, TPAR4, and TPAR5, were performed using density functional theory, and the electronic absorption properties were investigated via time-dependent density functional theory with polarizable continuum model for solvent effects. The population analysis indicates that the donating electron capability of TPA is better than that of indoline group. The reduction driving forces for the oxidized D131 and TPAR1 are slightly larger than that of other dyes because of their lower highest occupied molecular orbital level. The absorption properties and molecular orbital analysis suggest that the TPA and 4-(2,2diphenylethenyl)phenyl substituent indoline groups are effective chromophores in intramolecular charge transfer (IMCT), and they play an important role in sensitization of dye-sensitized solar cells (DSCs). The better performance of D205 in DSCs results from more IMCT excited states with larger oscillator strength and higher light harvesting efficiency. While for TPA dyes, the longer conjugate bridges generate the larger oscillator strength and light harvesting efficiency, and the TPAR1 and TPAR4 have larger free energy change for electron injection and dye regeneration.     

Molecular Design of Interfacial Modifiers for Polymer‐Inorganic Hybrid Solar Cells

The heterojunction of poly(3‐hexylthiophene) (P3HT) and TiO₂ in hybrid solar cells is systematically engineered with four cyanoacrylic acid‐containing conjugated molecules with various lowest unoccupied molecular orbital (LUMO) levels, WL‐1 to WL‐4, which are prepared by the formylation of thiophene derivatives in a Vilsmeier–Haack reaction, followed by treatment with cyanoacetic acid. The optical characteristics, redox properties, and intrinsic dipole moments of these interfacial modifiers (IMs) are examined using UV‐vis spectrophotometry, cyclic voltammetry, and density functional theory calculations. Using cyanoacrylic acid as a terminal anchoring group in IMs increases the electron affinity in regions close to the titania surface and forms a molecular dipole that is orientated away from the TiO₂ surface, enabling both open‐circuit voltage (V_OC) and short‐circuit current density to be increased simultaneously. Photovoltaic measurements demonstrate that V_OC increases with the dipole moment of IMs along the molecular backbone. Moreover, the external quantum efficiency (EQE) spectra display a bimodal distribution, revealing that both IMs and P3HT contribute to the photocurrent. The EQE at 570 nm is identified as characteristic of P3HT. More importantly, the LUMO of the IMs decisively determines the dissociation efficiency of P3HT excitons. The device based on P3HT/WL‐4/TiO₂ exhibits the highest power conversion efficiency of 2.87%.     

Quantitative structure activity relationships of some pyridine derivatives as corrosion inhibitors of steel in acidic medium

Quantum chemical calculations using the density functional theory (B3LYP/6-31G* DFT) and semi-empirical AM1 methods were performed on ten pyridine derivatives used as corrosion inhibitors for mild steel in acidic medium to determine the relationship between molecular structure and their inhibition efficiencies. Quantum chemical parameters such as total negative charge (TNC) on the molecule, energy of highest occupied molecular orbital (E _HOMO), energy of lowest unoccupied molecular orbital (E _LUMO) and dipole moment (μ) as well as linear solvation energy terms, molecular volume (Vi) and dipolar-polarization (π*) were correlated to corrosion inhibition efficiency of ten pyridine derivatives. A possible correlation between corrosion inhibition efficiencies and structural properties was searched to reduce the number of compounds to be selected for testing from a library of compounds. It was found that theoretical data support the experimental results. The results were used to predict the corrosion inhibition of 24 related pyridine derivatives.     

Antioxidant properties of Aloe vera components: a DFT theoretical evaluation

Prediction of the antioxidant activity of three Aloe vera components (aloesone, aloe-emodin, and isoeleutheol) was performed based on density functional theory calculations using the B3LYP hybrid functional and the 6–311++ G** basis set. Calculation of highest occupied molecular orbital (HOMO), lowest occupied molecular orbital (LUMO), and E_gap revealed that aloe-emodin has the lowest E_gap value, indicating good antioxidant activity. Also in terms of electron affinity, softness, electrophilicity, and chemical potential, aloe-emodin is a potent structure with potential high radical scavenging activity. Calculation of the ionisation potential revealed that isoeleutherol likely also possesses a high degree of antiradical scavenging. To study the conjugating system of the radicals, density plots of HOMO, natural bond orbital analyses, and spin density plots were used. According to calculations, the isoeleutherol radical is more delocalised and the most stable radical. Calculated proton affinity values revealed that the most probable antioxidant mechanism is sequential proton loss-electron transfer. Our results were compared with available experimental data. Published experimental data were found to correlate well with our theoretical predictions. These results support the usefulness of theoretical calculations not only for identifying potentially useful structures of studied compounds but also for predicting their relative activity.     

Ultrafast Charge Generation Pathways in Photovoltaic Blends Based on Novel Star‐Shaped Conjugated Molecules

The quest for new materials is one of the main factors propelling recent advances in organic photovoltaics. Star‐shaped small molecules (SSMs) have been proven promising candidates as perspective donor material due to the increase in numbers of excitation pathways caused by the degeneracy of the lowest unoccupied molecular orbital (LUMO) level. In order to unravel the pathways of the initial photon‐to‐charge conversion, the photovoltaic blends based on three different SSMs with a generic structure of N(phenylene‐nthiophene‐dicyanovinyl‐alkyl)₃ (n = 1–3), and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) acceptor are investigated by ultrafast photoinduced absorption spectroscopy assisted by density functional theory calculations. It is shown that both electron transfer from SSMs to PC₇₁BM and hole transfer from PC₇₁BM to SSMs are equally significant for generation of long‐lived charges. In contrast, intramolecular (intra‐SSM) charge separation results in geminate recombination and therefore constitutes a loss channel. Overall, up to 60% of long‐lived separated charges are generated at the optimal PC₇₁BM concentrations. The obtained results suggest that further improvement of the SSM‐based solar cells is feasible via optimization of blend morphology and by suppressing the intra‐SSM recombination channel.     

A novel dihydrocoumarin under experimental and theoretical characterization

Coumarins are natural and synthetic active ingredients widely applied in diverse types of medicinal treatments, such as cancer, inflammation, infection, and enzyme inhibition (monoamine oxidase B). Dihydrocoumarin compounds are of great interest in organic chemistry due to their structural versatilities and, as part of our investigations concerning the structural characterization of small molecules, this work focuses on crystal structure and spectroscopic characterization of the synthesized and crystallized compound 4-(4-methoxyphenyl)-3,4-dihydro-chromen-2-one (C₁₆H₁₄O₃). Additionally, a theoretical calculation was performed using density functional theory to analyze the sites where nucleophilic or electrophilic attack took place and to examine the molecular electrostatic potential surface. Throughout all of these calculations, both density functional theory and Car–Parrinello molecular dynamics were performed by fully optimized geometry. The spectroscopic analysis indicated the presence of aromatic carbons and hydrogen atoms, and also the carbonyl and methoxy groups that were confirmed by the crystallographic structure. The C₁₆H₁₄O₃ compound has a non-classical intermolecular interaction of type C–H???O that drives the molecular arrangement and the crystal packing. Moreover, the main absorbent groups were characterized throughout calculated harmonic vibrational frequencies. Also, natural bond orbital analysis successfully locates the molecular orbital with π-bonding symmetry and the molecular orbital with π* antibonding symmetry. Finally, the gap between highest occupied and lowest unoccupied molecular orbitals implies in a high kinetic stability and low chemical reactivity of title molecule.     

Molecular dynamics and quantum chemical studies of solvent effects on cyclo glycylglycine and glycylalanine dipeptides

Hydrogen bond (H-bond) interactions between the two cyclo dipeptides, cyclo(glycyl-glycine) (CGG) and cyclo(glycyl-alanine) (CGA), and water have been studied using molecular dynamics (MD) and quantum chemical methods. The MD studies have been carried out on CGG and CGA in water using fixed charge force field (AMBER ff03) for over 10 ns with a MD time step of 2 fs. The results of this study show that the solvation pattern influences the conformations of the cyclo dipeptides. Following molecular simulations, post Hartree–Fock and density functional theory methods have been used to explore the molecular properties of the cyclo dipeptides in gaseous and aqueous phase environments. The self-consistent reaction field theory has been used to optimise the cyclopeptides in diethyl ether (? = 4.3) and water (? = 78.5), and the solvent effects have been analysed. A cluster of eight water molecules leads to the formation of first solvation shell of CGG and CGA and the strong H-bonding mainly contributes to the interaction energies. The H-bond interactions have been analysed by the calculation of electron density ρ(r) and its Laplacian ▽²ρ(r) at bond critical points using atoms in molecules theory. The natural bond orbital analysis was carried out to reveal the nature of H-bond interactions. In the solvated complexes, the keto carbons registered the maximum NMR chemical shifts.     

Computational study of the NO,SO<Subscript>2</Subscript>, and NH<Subscript>3</Subscript> adsorptions on fragments of 3N-graphene and Al/3N graphene

The adsorption properties of common gas molecules (NO, NH₃, and SO₂) on the surface of 3N-graphene and Al/3N graphene fragments are investigated using density functional theory. The adsorption energies have been calculated for the most stable configurations of the molecules on the surface of 3N-graphene and Al/3N graphene fragments. The adsorption energies of Al/3N graphene-gas systems are ?220.5 kJ mol^?1 for Al/3NG-NO, ?111.9 kJ mol^?1 for Al/3NG-NH₃, and ?347.7 kJ mol^?1 for Al/3NG-SO₂, respectively. Compared with the 3N-graphene fragment, the Al/3N graphene fragment has significant adsorption energy. Furthermore, the molecular orbital, density of states, and electron densities distribution were used to explore the interaction between these molecules and the surface. We found that orbital hybridization exists between these molecules and the Al/3N graphene surface, which indicates that doping Al significantly increases the interaction between the gas molecules and Al/3N graphene. In addition, compared with Li, Al can more powerfully enhance adsorption of the 3N-graphene fragment. The results indicate that Al/3N graphene can be viewed as a new nanomaterial adsorbent for NO, NH₃, and SO₂.     

桉树与红锥混交对土壤养分及林下植物功能群的影响

桉树人工林对生态环境的影响一直是全球性争议的热点问题,桉树与珍贵乡土树种混交的生态环境效应备受关注。为探究桉树混交营林措施对林地土壤养分及林下植物功能群的影响,该研究以桉树纯林(PE)、桉树×红锥混交林(MEC)和红锥纯林(PCH)为对象,开展了林下植物群落及环境因子的调查测定。研究结果显示：不同林分的土壤理化性质具有显著差异,混交林的土壤pH、有效氮(AN)和有效磷(AP)含量显著高于纯林;而土壤含水量(SMC)、有机碳(SOC)、总氮(TN)含量及C∶N和C∶P在混交林中没有显著优势,并呈现PEMEC>PCH的趋势。混交林显著增加林下木本植物功能群(WFG)的物种丰富度,而PCH显著增加蕨类植物功能群(FeFG)的物种丰富度。混交林的WFG和禾草植物功能群(GFG)的重要值均显著高于红锥纯林,而红锥纯林FeFG的重要值显著高于混交林。主坐标分析结果表明,MEC与PE的林下植物功能群组成差异不显著,但与PCH的差异显著;冗余分析结果揭示了AN和AP是WFG占优势的主要影响因子,SMC、TN...     

Electronic structure and conformational properties of <Emphasis Type="Italic">1H</Emphasis>-indole-3-acetic acid

The conformational space of 1H-Indole-3-Acetic Acid (IAA) was scanned using molecular dynamics at semiempirical level, and complemented with functional density calculations at B3LYP/6-31G** level, 14 conformers of lowest energy were obtained. Electronic distributions were analyzed at a higher calculation level, thus improving the basis set (B3LYP/6-311++G**). A topological study based on Bader’s theory (AIM: atoms in molecules) and natural bond orbital (NBO) framework performed with the aim to analyze the stability and reactivity of the conformers allowed the understanding of electronic aspects relevant in the study of the antioxidant properties of IAA. Intramolecular hydrogen bonds were found and were characterized as blue-shifting hydrogen bonding interactions. Furthermore, molecular electrostatic potential maps (MEPs) were obtained and analyzed in the light of AIM and NBO results, thus showing subtle but essential features related not only to reactivity but also with intramolecular weak interactions, charge delocalization and structure stabilization.     

Relating Frontier Orbital Energies from Voltammetry and Photoelectron Spectroscopy to the Open‐Circuit Voltage of Organic Solar Cells

For 19 diketopyrrolopyrrole polymers, the highest occupied molecular orbital (HOMO) energies are determined from i) the oxidation potential with square‐wave voltammetry (SWV), ii) the ionization potential using ultraviolet photoelectron spectroscopy (UPS), and iii) density functional theory (DFT) calculations. The SWV HOMO energies show an excellent linear correlation with the open‐circuit voltage (V_oc) of optimized solar cells in which the polymers form blends with a fullerene acceptor ([6,6]‐phenyl‐C₆₁‐butyl acid methyl ester or [6,6]‐phenyl‐C₇₁‐butyl acid methyl ester). Remarkably, the slope of the best linear fit is 0.75 ± 0.04, i.e., significantly less than unity. A weaker correlation with V_oc is found for the HOMO energies obtained from UPS and DFT. Within the experimental error, the SWV and UPS data are correlated with a slope close to unity. The results show that electrochemically determined oxidation potentials provide an excellent method for predicting the V_oc of bulk heterojunction solar cells, with absolute deviations less than 0.1 V.     

The stability of the pheromones of xylophagous insects to environmental factors: An evaluation by quantum chemical analysis

The ground and excited states of the pheromone molecules produced by xylophagous insects (the bark beetle Ips typographus L., the black fir sawyer beetle Monochamus urussovi Fisch., and the black pine sawyer M. galloprovincialis Oliv.) were modeled using a quantum chemical method utilizing DFT (density functional theory) with the B3LYP functional. The absorption wavelengths (energies) and dipole moments were calculated; the transitions of electrons from occupied to empty molecular orbitals were considered. The computed data were used to assess the stability of pheromone molecules exposed to environmental factors, such as solar radiation and humidity.     

Electronic structure and band gap engineering of ZnO-based semiconductor alloy films

We have conducted first-principles total-energy density functional calculations to study the atomic structures, band structures and electronic structures of Zn_1 ? xM_xO (M = Be, Mg, Cd, Ag, Cu) semiconductor alloys. The Heyd–Scuseria–Ernzerhof hybrid functional has been performed to yield lattice constants and band gaps of Zn_1 ? xM_xO semiconductor in much better agreement with experimental data than with the standard local exchange correlation functional. We found that the strong coupling between O 2p and Cu 3d or Ag 4d bands plays a key role in narrowing of band gaps and leading to the half-metallic behaviour interpreted with the unique spatial distribution pattern between the highest occupied molecular orbital and the lowest unoccupied molecular orbital.     

Side‐Chain Engineering for Enhancing the Properties of Small Molecule Solar Cells: A Trade‐off Beyond Efficiency

Three small molecules with different substituents on bithienyl‐benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) units, BDTT‐TR (meta‐alkyl side chain), BDTT‐O‐TR (meta‐alkoxy), and BDTT‐S‐TR (meta‐alkylthio), are designed and synthesized for systematically elucidating their structure–property relationship in solution‐processed bulk heterojunction organic solar cells. Although all three molecules show similar molecular structures, thermal properties and optical band gaps, the introduction of meta‐alkylthio‐BDTT as the central unit in the molecular backbone substantially results in a higher absorption coefficient, slightly lower highest occupied molecular orbital level and significantly more efficient and balanced charge transport property. The bridging atom in the meta‐position to the side chain is found to impact the microstructure formation which is a subtle but decisive way: carrier recombination is suppressed due to a more balanced carrier mobility and BDTT based devices with the meta‐alkylthio side chain (BDTT‐S‐TR) show a higher power conversion efficiency (PCE of 9.20%) as compared to the meta‐alkoxy (PCE of 7.44% for BDTT‐TR) and meta‐alkyl spacer (PCE of 6.50% for BDTT‐O‐TR). Density functional density calculations suggest only small variations in the torsion angle of the side chains, but the nature of the side chain linkage is further found to impact the thermal as well as the photostability of corresponding devices. The aim is to provide comprehensive insight into fine‐tuning the structure–property interrelationship of the BDTT material class as a function of side chain engineering.     

Experimental and theoretical investigations of spectroscopic properties of azobenzene derivatives in solution

The UV-Vis spectra of series of polymethylmethacrylate (PMMA) copolymers with attached trans-azobenzene derivatives were measured in 1,1,2-trichloroethane. In order to gain some insight into the recorded spectra, the quantum chemical calculations were performed for the substituted azobenzenes using both configuration interaction with single excitations method (CIS) as well as density functional theory (DFT) with B3LYP and PBE0 functionals. The calculations were performed in solvent. In particular, we found that the PBE0 excitation energies are in very good agreement with the experimental data. Figure The plots of orbital contour surfaces for molecule II. The molecular orbitals were calculated at the PBE0/6-311++G(d,p) level of theory. The upper plot presents contour surface of HOMO and the lower presents contour surface of LUMO. Shown are the contour surfaces of orbital amplitude 0.04 (red) and -0.04 (blue)     

Comparative theoretical study of the structures and stabilities of four typical gadolinium carboxylates in different scintillator solvents

The structural properties and stabilities of four typical gadolinium carboxylates (Gd-CBX) in toluene, linear alkyl benzene (LAB), and phenyl xylyl ethane (PXE) solvents were theoretically studied using density functional theory (DFT/B3LYP with the basis sets 6-311G(d) and MWB54) and the polarizable continuum model (PCM). The average Gd–ligand interaction energies (E _int, corrected for dispersion) and the values of the energy gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital (\( \varDelta \) _HL) for the gadolinium complexes were calculated to compare the relative stabilities of the four Gd-CBX molecules in the three liquid scintillator solvents. According to the calculations, the values of E _int and \( \varDelta \) _HL for Gd-CBX in LAB are larger than the corresponding values in PXE and toluene. Gd-CBX may therefore be more compatible with LAB than with PXE and toluene. It was also found that, in the three scintillator solvents, the stabilities of the four Gd-CBX molecules increase in the order Gd-2EHA?<?Gd-2MVA?<?Gd-pivalate?<?Gd-TMHA.     

Conformational and electronic (AIM/NBO) study of unsubstituted A-type dimeric proanthocyanidin

The conformational space of the unsubstituted A-type dimeric proanthocyanidin was scanned using molecular dynamics at a semiempirical level, and complemented with functional density calculations. The lowest energy conformers were obtained. Electronic distributions were analysed at a higher calculation level, thus improving the basis set. A topological study based on Bader’s theory (AIM: atoms in molecules) and natural bond orbital (NBO) framework was performed. Furthermore, molecular electrostatic potential maps (MEPs) were obtained and analysed. NMR chemical shifts were calculated at ab initio level and further compared with previous experimental values; coupling constants were also calculated. The stereochemistry of the molecule is thoroughly discussed, revealing the key role that hyperconjugative interactions play in defining experimental trends. These results show the versatility of geminal spin–spin coupling ²J(C-1′,O) as a probe for stereochemical studies of proanthocyanidins.     

Identification of anti-filarial leads against aspartate semialdehyde dehydrogenase of Wolbachia endosymbiont of Brugia malayi: combined molecular docking and molecular dynamics approaches

Lymphatic filariasis is a debilitating vector borne parasitic disease that infects human lymphatic system by nematode Brugia malayi. Currently available anti-filarial drugs are effective only on the larval stages of parasite. So far, no effective drugs are available for humans to treat filarial infections. In this regard, aspartate semialdehyde dehydrogenase (ASDase) in lysine biosynthetic pathway from Wolbachia endosymbiont Brugia malayi represents an attractive therapeutic target for the development of novel anti-filarial agents. In this present study, molecular modeling combined with molecular dynamics simulations and structure-based virtual screening were performed to identify potent lead molecules against ASDase. Based on Glide score, toxicity profile, binding affinity and mode of interactions with the ASDase, five potent lead molecules were selected. The molecular docking and dynamics results revealed that the amino acid residues Arg103, Asn133, Cys134, Gln161, Ser164, Lys218, Arg239, His246, and Asn321 plays a crucial role in effective binding of Top leads into the active site of ASDase. The stability of the ASDase-lead complexes was confirmed by running the 30 ns molecular dynamics simulations. The pharmacokinetic properties of the identified lead molecules are in the acceptable range. Furthermore, density functional theory and binding free energy calculations were performed to rank the lead molecules. Thus, the identified lead molecules can be used for the development of anti-filarial agents to combat the pathogenecity of Brugia malayi.     

Achieving Both Enhanced Voltage and Current through Fine‐Tuning Molecular Backbone and Morphology Control in Organic Solar Cells

It is a great challenge to simultaneously improve the two tangled parameters, open circuit voltage (V_oc) and short circuit current density (J_sc) for organic solar cells (OSCs). Herein, such a challenge is addressed by a synergistic approach using fine‐tuning molecular backbone and morphology control simultaneously by a simple yet effective side chain modulation on the backbone of an acceptor–donor–acceptor (A–D–A)‐type acceptor. With this, two terthieno[3,2‐b]thiophene (3TT) based A–D–A‐type acceptors, 3TT‐OCIC with backbone modulation and 3TT‐CIC without such modification, are designed and synthesized. Compared with the controlled molecule 3TT‐CIC, 3TT‐OCIC shows power conversion efficiency (PCE) of 13.13% with improved V_oc of 0.69 V and J_sc of 27.58 mA cm^?2, corresponding to PCE of 12.15% with V_oc of 0.65 V and J_sc of 27.04 mA cm^?2 for 3TT‐CIC–based device. Furthermore, with effective near infrared absorption, 3TT‐OCIC is used as the rear subcell acceptor in a tandem device and gave an excellent PCE of 15.72%.     

Determination of copper binding in <Emphasis Type="Italic">Pseudomonas putida</Emphasis> CZ1 by chemical modifications and X-ray absorption spectroscopy

Previously performed studies have shown that Pseudomonas putida CZ1 biomass can bind an appreciable amount of Cu(II) and Zn(II) ions from aqueous solutions. The mechanisms of Cu- and Zn-binding by P. putida CZ1 were ascertained by chemical modifications of the biomass followed by Fourier transform infrared and X-ray absorption spectroscopic analyses of the living or nonliving cells. A dramatic decrease in Cu(II)- and Zn(II)-binding resulted after acidic methanol esterification of the nonliving cells, indicating that carboxyl functional groups play an important role in the binding of metal to the biomaterial. X-ray absorption spectroscopy was used to determine the speciation of Cu ions bound by living and nonliving cells, as well as to elucidate which functional groups were involved in binding of the Cu ions. The X-ray absorption near-edge structure spectra analysis showed that the majority of the Cu was bound in both samples as Cu(II). The fitting results of Cu K-edge extended X-ray absorption fine structure spectra showed that N/O ligands dominated in living and nonliving cells. Therefore, by combining different techniques, our results indicate that carboxyl functional groups are the major ligands responsible for the metal binding in P. putida CZ1.