Low Ionization Potential Research Articles

Quantum-chemical study of lutetium and ytterbium bis- and tetrakis(phthalocyaninates)

DFT calculations with B3LYP and PBE0 functionals have been carried out to determine the structural parameters, vibrational frequencies, and quadrupole moments of double-decker heavy lanthanide phthalocyaninates Pc2Lu, (Pc2Lu)+, (Pc2Lu)–, Pc2Yb, (Pc2Yb)+, and (Pc2Yb)–. Free valence of the Pc moiety [0.5 in Pc2Lu and Pc2Yb; 1.0 in (Pc2Lu)+ and (Pc2Yb)+] is delocalized in small fractions over the carbon atoms. The Pc2Lu и Pc2Yb molecules have a high electron affinity (3.2 eV) and a low ionization potential (6.1–6.3 eV). Calculations predict formation of quadruple-decker supercomplex Yb(Pc2Lu)2 from two Pc2Lu molecules and an Yb atom via an exothermic process. The equilibrium structure of the molecules and ions can be characterized by D4d point symmetry group.

Atmospheric‐pressure nonthermal plasma synthesis of ammonia over ruthenium catalysts

Atmospheric‐pressure nonthermal plasma was used to synthesize ammonia from nitrogen and hydrogen over ruthenium catalysts. Formation of NH3 in a N2‐H2 mixture altered the plasma characteristics due to the low ionization potential of NH3 (10.15 eV). The optimum gas ratio was found at N2:H2 = 4:1 by volume (i.e., N2‐rich conditions). When plasma was operated at a temperature below 250 °C, the NH3 concentration increased linearly with increasing specific input energy (SIE). For the Ru(2)‐Mg(5)/γ‐Al2O3 catalyst at 250 °C, pulse energization was four times more efficient than the AC energization case. The presence of RuO2 was found to be beneficial for the NH3 synthesis via plasma‐catalysis. The addition of a small amount of O2 was found to be effective for the in situ regeneration of the deactivated catalyst. The effect of metal promoters was in the order of Mg > K > Cs > no promoter.

3,7-Diaryl substituted 10-butylphenoxazines as new hole transporting materials for organic light emitting devices

Phenyl, naphthyl or vinylphenyl substituted 10-butylphenoxazines were synthesized by a multi-step synthetic rout. The materials were examined by various techniques including thermogravimetry, differential scanning calorimetry, electron photoemission spectroscopy and time of flight method. The materials were found to show adequate thermal stability having initial thermal degradation temperatures in the range of 280–310 °C. Glass transition temperatures of the low-molar-mass materials were in the rage of 31–65 °C. The electron photoemission spectra of thin layers of the derivatives showed low ionization potentials of 5.1–5.15 eV. Hole drift mobilities in thin layers of some derivatives exceeded 2 × 10−4 cm2V−1s−1 at an electric field of 4 × 105 Vcm−1s at room temperature. These materials have been tested as hole transporting layers in electroluminescent bilayer OLEDs with Alq3 as the emitter. The device with hole transporting layer comprised of 10-butyl-3,7-di(1-naphthyl)phenoxazine exhibited the best overall performance with very low turn-on voltage of 3.6 V, a maximum luminance efficiency of 2 cd/A and maximum brightness of about 7420 cd/m2.

Novel fluorene/indole-based hole transport materials with high thermal stability for efficient OLEDs

A series of novel hole transport materials based on fluorene and indole were designed, synthesized and well characterized. The carbazole and triphenylamine groups, which have excellent charge carrier mobility and low ionization potential, were introduced by coupling reactions. Ultraviolet–visible (UV–vis) spectral, photoluminescence (PL) spectral, cyclic voltammetry (CV), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements were performed to investigate the photophysical properties, thermal properties and electrochemical properties of these materials. The results implied that all these materials have excellent thermal stabilities with the 5% weight loss at 409–456 °C. The OLED devices based on the as-prepared materials were fabricated to investigate their hole transport ability. It turns out that device based on compound c exhibited the best performance with a maximum current efficiency of 3.74 cd/A and turn-on voltage at 4.0 V. The device performances indicated that the as-prepared materials can serve as highly efficient hole transport materials in OLED devices.

Tuning the physical properties of organic sensitizers by replacing triphenylamine with new donors for dye sensitized solar cells - a theoretical approach

New donor molecules with low ionization potential have been theoretically designed by replacing the benzene moieties in triphenylamine (TPA) with thiophene as well as furan. The designed new donors also exhibited planar structure, making an angle of 120° around the nitrogen atom that results in resonance effects through π-bonds of aryl rings. New sensitizers have been theoretically studied using DFT and TD-DFT by adopting these designed donors. UV–Vis absorption spectra, light harvesting ability (LHE) and electron injection ability (ΔGinject) of the designed sensitizers have been calculated by taking L0 as reference. Orbital overlapping between donor and acceptor facilitates intra-molecular charge transfer, thereby increasing the interfacial electron injection from the sensitizer to the semiconductor nanoparticles. Our theoretical results demonstrate that sensitizers DTPA-AA and DFPA-AA have broader absorption and lower ΔGinject respectively compare to L0, this opens a new way for designing sensitizers for dye sensitized solar cells (DSSCs). All the dyes designed were found to be good light harvesters.

Assemblage of Superalkali Complexes with Ever Low-Ionization Potentials.

A simple recipe is proposed for the obtention of new molecules with even lower vertical ionization potential (VIP): to decorate an atom of an electronegative element with superalkali species in number that exceeds its formal valence by one. For instance, density functional theory calculations show that by using the superalkali Li3O cluster (VIP = 3.83 eV) as building blocks decorating the O atom one obtains VIP = 3.33 eV for the Li9O4 cluster, which is lower than the calculated VIP for Cs (3.89 eV) and Li (5.39 eV). This feature is systematic, as confirmed by calculated results on Li-F and Li-S clusters as well. The calculated binding energy per atom of the large-sized species exceeds by far that of LiF (134.7 kcal/mol).

Detailed surface study of adsorbed nickel on Al12N12 nano-cage

The geometries and electronic structures of Ni-adsorbed Al12N12 (AlN) nano-cage are studied by density functional theory. A number of different structures varying in the position and orientation of nickel on the surface of the nano-cage are studied. Binding energies, band structures, total density of states, natural bond orbital charges, and electron density differences of Ni-adsorbed Al12N12 nano-cage were calculated, and analyzed in comparison with pure AlN nano-cage. The adsorption energies are in the range of (−110)–(−113) kcalmol−1 for three adsorption sites (P1–P3), and about −86kcalmol−1 for P4. High binding energies for these geometries suggest strong chemisorption of nickel on AlN nano-cage. Moreover, dissociation of AlN bond is observed concurrent with the formation of NiAl and NiN bonds when the Ni atom is adsorbed on the nano-cage. Results from the calculations also reveal that there is significant charge transfer from the nano-cage to the metal atom which changes the location of HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) resulting in reductions in the Egap (EHOMO-ELUMO). The HOMO-LUMO gap for P4 geometry is 1.79eV which is much lower than the band gap for pure AlN nano-cage (3.93eV). The band gap for P1, P2 and P3 geometries is 2.90, 2.79 and 3.18eV, respectively. The decrease in band gap is attributed to the push of outer d electrons of the transition metals to become more diffuse like. The HOMOs in all geometries have densities on Ni atom whereas the densities in LUMO are distributed on the entire skeleton. The results revealed that Ni adsorption provides N-type conduction which makes it an ideal adsorbent for practical applications in magnetism, catalysis and other areas. Reactivity descriptors indicate an increase in electrophilic character of Ni-adsorbed nano-cages compared to pure AlN nano-cage. The electron affinity and softness are highest for P4 geometry whereas the lowest ionization potential and hardness are calculated for P4.

Cyclopropenimine as pincer ligand and strong electron donor in proton sponges

The basicity of cyclopropenimines (CPIs) and cyclopropenimino‐based proton sponges is investigated by means of density functional theory (DFT) calculations and for the first time directly compared with the basicity of phosphazenes. It is found that CPIs are more basic than the corresponding phosphazenes in the gas phase. Proton sponges based on CPI as pincer ligands also possess higher or at least the same gas‐phase proton affinity as proton sponges based on phosphazenes. However, in comparison with phosphazenes, CPI‐based pincer ligands possess greater conformational flexibility, which enables almost complete avoidance of nitrogen lone pairs. This leads to the substantially smaller destabilization of neutral base in CPI proton sponges. Utilizing homodesmotic reactions, we have shown that significant contribution to the proton affinity of CPI proton sponges is an electron‐donating effect of the second CPI substituent, whereas only a smaller portion of the stabilization energy should be attributed to intramolecular hydrogen bond. Further, it was shown that tetrasubstituted CPI naphthalenes possess very low ionization potential, which qualifies them as very strong electron donors. Finally, utilizing cyclopropenimino substituents, it was found that theoretical gas basicity limit of 370 kcal mol−1 recently calculated by Leito and coworkers could be extended beyond 370 kcal mol−1 in a case of cyclopropenimino phosphorus carbenes and cylopropenimino phosphorus ylides. Copyright © 2016 John Wiley & Sons, Ltd.

Band Alignments, Valence Bands, and Core Levels in the Tin Sulfides SnS, SnS2, and Sn2S3: Experiment and Theory

Tin sulfide solar cells show relatively poor efficiencies despite attractive photovoltaic properties, and there is difficulty in identifying separate phases, which are also known to form during Cu2ZnSnS4 depositions. We present X-ray photoemission spectroscopy (XPS) and inverse photoemission spectroscopy measurements of single crystal SnS, SnS2, and Sn2S3, with electronic-structure calculations from density functional theory (DFT). Differences in the XPS spectra of the three phases, including a large 0.9 eV shift between the 3d5/2 peak for SnS and SnS2, make this technique useful when identifying phase-pure or mixed-phase systems. Comparison of the valence band spectra from XPS and DFT reveals extra states at the top of the valence bands of SnS and Sn2S3, arising from the hybridization of lone pair electrons in Sn(II), which are not present for Sn(IV), as found in SnS2. This results in relatively low ionization potentials for SnS (4.71 eV) and Sn2S3 (4.66 eV), giving a more comprehensive explanation as to...

Electrochemical Characterization of Synthetic Hybrid DNA Molecular Wires

As a viable solution to long-term stability problems associate with DNA molecular wires along with the additional benefits of tuning their conductivity, hybrid DNA molecular wires made of natural base-pairs and synthetic base-pairs, which have lower ionization potentials and a more π orbital overlapping, offer an attractive option. A strong synthetic nucleotide candidate is tricyclic cytosine analogue (such as (8-MeO)tC), which we show has (i) a lower ionization potential (~ 0.65V) compared to natural nucleotides, G (1.29V), C (1.6V), A (1.42V), T (1.7V) and (ii) more π-orbital stacking due to its tricyclic structure. Moreover, to illuminate the importance of the π orbital stack to the conductivity of DNA molecular wires, in this paper, we compared the conductivity of wild-type (WT) DNA and DNA sequences containing mismatched base-pairs that perturb the π orbital stack. Lower conductivity was obtained when modifying the surface of the gold electrodes with both WT and mismatched DNA. Further, chips functionalized with DNA sequences with mismatched base-pairs were observed to have lower conductivity than those functionalized with WT DNA sequences.

Influence of laser on the droplet behavior in short-circuiting, globular, and spray modes of hybrid fiber laser-MIG welding

The effects of laser on the droplet behavior in short-circuiting, globular, and spray modes of hybrid fiber laser-MIG welding were studied. Transfer sequence of a droplet, welding current wave and morphology of plasma in the three modes of arc welding and hybrid welding were comparatively investigated. Compared with arc welding, the transfer frequency and landing location of droplet in the three modes of hybrid welding changed. In short-circuiting and globular modes, the droplet transfer was promoted by the laser, while the droplet transfer was hindered by the laser in spray mode. The magnitudes and directions of electromagnetic force and plasma drag force acting on the droplet were the keys to affect the droplet behavior. The magnitudes and directions of electromagnetic force and plasma drag force were converted due to the variation of the current distribution into the droplet, which were caused by the laser induced plasma with low ionization potential.

Electrochemical Characterization of Synthetic Hybrid DNA Molecular Wires

Over the past several years, considerable amount of research have been conducted on DNA conductivity studies and charge transfer mechanisms for potential applications in micro and nano-scale electronic devices. In general, there is a consensus that DNA molecule behaves as a one-dimensional aromatic crystal with π-electron conductivity. Along these lines, our recent work has shown that DNA molecular wire’s electrical properties are strongly influenced by the ionization potential and percentage content of its base-pairs that form these π-orbital stacking. Our previous work has also shown the effect of external effects such as humidity, electrical fields, and UV illumination on the long-term stability of DNA molecular wires. In general, with time, there is measurable significant decrease in the conductivity in DNA wires exposed to ambient conditions. Such external effects could also result in the physical change of DNA molecular wires that in turn compromise their suitability as nanoelectronic component. As a viable solution to long-term stability problems with DNA molecular wires and also tuning their conductivity, we are currently working on synthesizing hybrid DNA molecular wires made of natural base-pairs and synthetic base-pairs with lower ionization potentials and more π-orbital overlapping. One strong candidate is tricyclic cytosine analogue (such as (8-MeO) tC0), a synthetic unnatural base, which possesses (i) a lower ionization potential (~ 0.65 V) compared to natural bases, G (1.29 V), C (1.6 V), A (1.42 V), T (1.7 V) and (ii) more π-orbital stacking than the natural bases due to its tricyclic structure. This unnatural base can be a good choice as it minimally perturbs the structure of B-form DNA. Subsequently, we investigate the charge transfer mechanism of short hybrid doubled stranded DNA (16 bp) consisting of both natural and unnatural bases and compared it to the natural DNA strand of the same length. The whole hybrid DNA sequence is NH2-5’-AtC0TACAGTCATCGCtC0tC0-3’ where some bases were substitute with tricyclic cytosine analogues (tC0). Two methods are used to study the charge transport through hybrid DNA wires. One is based on the charge transport between donor and acceptor (oxidant and hole trap). The oxidant (donor) is the metallointercalator which has positive charge with either Ru or Rh complex. This intercalator does not perturb the structure of the DNA π stacking as it binds covalently with DNA. The hole trap is two (8-MeO) tC0 molecules in a row, as it can potentially have the lowest ionization potential in the DNA sequence. The donor is then photo-excited and the fluorescence of the donor quenched through the DNA strand during charge transfer to the acceptor. The Ru or Rh complex are positioned at the 5’ of the DNA sequence, apart from the hole trap. A DNA 5 ‘terminus has to be terminated with amine group in order to interact with carboxyl group of Ru or Rh complex through EDC-NHS reaction. The other method is based on electrochemical detection. The sequence to be used is the same as the first method, however, it is terminated with the thiol group SH-5’-AtC0TACAGTCATCGCtC0tC0-3’ in order to be attached easily to gold electrodes. The radox active material (Methylen Blue) acts as an intercalator and its electrocatalytic signal is measured while the electrons pass through the DNA strands attached to the surface. The DNA strands are in the Ferrocyanide solution [Fe(CN)6]-3 which can be reduced by the reduction of methyl blue. The chronocoulometry techniques is then used to measure the electron transport in DNA strand. Between the two methods, we demonstrate that synthetic molecular wires consisting of both natural and strategically placed synthetic bases with lower ionization potential and π stacking will offer a stable and electrically tunable molecular wire.

Extended application of Kohn-Sham first-principles molecular dynamics method with plane wave approximation at high energy—From cold materials to hot dense plasmas

An extended first-principles molecular dynamics (FPMD) method based on Kohn-Sham scheme is proposed to elevate the temperature limit of the FPMD method in the calculation of dense plasmas. The extended method treats the wave functions of high energy electrons as plane waves analytically and thus expands the application of the FPMD method to the region of hot dense plasmas without suffering from the formidable computational costs. In addition, the extended method inherits the high accuracy of the Kohn-Sham scheme and keeps the information of electronic structures. This gives an edge to the extended method in the calculation of mixtures of plasmas composed of heterogeneous ions, high-Z dense plasmas, lowering of ionization potentials, X-ray absorption/emission spectra, and opacities, which are of particular interest to astrophysics, inertial confinement fusion engineering, and laboratory astrophysics.

Diversity of monomeric dioxo chromium species in Cr/silicalite-2 catalysts: A hybrid density functional study

The present paper deals with the theoretical characterization of the dioxo Cr species exchanged into the silicalite-2 structure via hybrid density functional theory with cluster models to represent the active site. The molecular models range from a simple mono silicon atom ring to more complex Cr–siloxane rings of 7T atoms. The common B3LYP and M06 density functionals were used for the calculations. The results indicate that the chemical hardness increases from a complex ring to a simple geminate type. Overall, the QTAIM calculations point to intermediate ionic–covalent nature of the Cr–oxygen bonds. An excellent correlation is found between the positive eigenvalue of the Hessian at the bond critical point with the CrO bond distance. Whereas the enthalpy change on the exchange reaction alters from −20.3 to 56.1kcal/mol at the M06/6-311+G∗ level, the binding energy lies in a shorter range of 907.5–926.6kcal/mol. As concluded from the Gibbs free energy changes on the exchange reaction with both of the methods, only the clusters of 4T size or larger would be formed spontaneously. However, M06 predicts ∼13% stronger bindings for the Cr ion. Overall, the electronic properties depend upon both the SiOCrOSi aperture size and the local configuration of the matrix. Furthermore, a fivefold coordination of Cr is accompanied with a lower ionization potential, a longer CrO distance, and a less negative charge on the terminal O atoms.

Global model of an iodine gridded plasma thruster

Most state-of-the-art electric space propulsion systems such as gridded and Hall effect thrusters use xenon as the propellant gas. However, xenon is very rare, expensive to produce, and used in a number of competing industrial applications. Alternatives to xenon are currently being investigated, and iodine has emerged as a potential candidate. Its lower cost and larger availability, its solid state at standard temperature and pressure, its low vapour pressure and its low ionization potential make it an attractive option. In this work, we compare the performances of a gridded ion thruster operating separately with iodine and xenon, under otherwise identical conditions using a global model. The thruster discharge properties such as neutral, ion, and electron densities and electron temperature are calculated, as well as the thruster performance parameters such as thrust, specific impulse, and system efficiencies. For similar operating conditions, representative of realistic thrusters, the model predicts similar thrust levels and performances for both iodine and xenon. The thruster efficiency is however slightly higher for iodine compared with xenon, due to its lower ionization potential. This demonstrates that iodine could be a viable alternative propellant for gridded plasma thrusters.

The Ideal and Real Gas Heat Capacity of Potassium Atoms at High Temperatures

The ideal gas heat capacity, Cp, of cesium atoms is calculated to high temperatures using statistical mechanics. There are a large number of electronic states in the state sum that determines the partition function: 174 known levels for cesium atoms below the first ionization potential. Thus, at high temperatures, Cp becomes very large unless the number of contributing states is constrained. Two arguments are used to do this. First, at high temperatures, the increased size of the atoms constrains the sum (Bethe method). Second, the existence of interacting charged species at higher temperatures, which lowers the ionization potential, constrains the sum (ionization potential lowering method). If atoms constitute a real gas obeying the virial equation of state, the lowest non-ideal contribution to Cp depends on the second derivative of the second virial coefficient, B″(T), which depends on the interaction potential energy curves between two atoms. When two ground-state (2S) cesium atoms interact, they follow either of two potential energy curves. When a 2S cesium atom interacts with a cesium atom in the first electronically excited (2P) state, they follow any of eight potential energy curves. The values of B″(T) for the ten states are determined, then averaged, and used to calculate the lowest order non-ideal contribution to Cp.

Toward a new paradigm for sonochemistry: Short review on nonequilibrium plasma observations by means of MBSL spectroscopy in aqueous solutions

This review summarizes recent studies of multibubble sonoluminescence (MBSL) in aqueous media in order to highlight new insights into the origin of the sonochemical activity. The observation of OH(C2Σ+–A2Σ+) emission band and a spectroscopic analysis of OH(A2Σ+–X2Πi) emission band in MBSL of water pre-equilibrated with noble gases revealed the formation of a nonequilibrium plasma inside the collapsing bubble (Te>Tv>Tr, where Te is an electron temperature, Tv is a vibrational temperature and Tr is a rotational (gas) temperature). The Te and Tv estimated using OH(A2Σ+–X2Πi) emission band increase with ultrasonic frequency. In Xe the Tv of OH(A2Σ+) state is much higher than in Ar most probably due to the lower ionization potential of Xe. The MBSL of C2∗ Swan band (d3Πg–a3Πu) measured in aqueous tert-butanol (t-BuOH) solutions correlates with the data obtained for OH(A2Σ+–X2Πi) emission band. Analysis of the gaseous products of t-BuOH sonolysis revealed a significant sonochemical activity even at high t-BuOH concentration when MBSL is totally quenched, indicating that drastic intrabubble conditions (plasma) are not necessarily accompanied by sonoluminescence. The nonequilibrium plasma model of cavitation allows to explain the reverse carbon isotope effect observed during the sonolysis of water in the presence of Ar/CO gas mixture.

Effect of the Nature of the Core on the Properties of the Star-Shaped Compounds Containing Bicarbazolyl Moieties

Three star-shaped compounds containing bicarbazolyl side arms and various core moieties are described. Bicarbazolyl moiety proves to be a stronger donor than single carbazolyl group, providing lower ionization potential and superior thermal and electrochemical stability. The influence of the central core, that is, 2,4,6-triphenyl-1,3,5-triazine, 1,3,5-triphenylbenzene, and 9-phenylcarbazole fragments, on the properties of the compounds is investigated and supported by DFT calculations. The dependence of photophysical properties on the rigidity and polarity of the media is discussed. Owing to the differences in molecular architecture, tuning of singlet and triplet energy values can be achieved. The synthesized compounds showed good hole-transporting properties with the mobility values exceeding 10–3 cm2 V–1 s–1.

Two soluble polymers with lower ionization potentials: doping and thermoelectric properties

By means of doping with LiTFSI solution in air, polymer PDTPT-C12 shows a thermoelectric power factor approaching 40 μW m−1 K−2 at 390 K.

Study of New Thiazole Based Pyridine Derivatives as Potential Corrosion Inhibitors for Mild Steel: Theoretical and Experimental Approach

Three new thiazole based pyridine derivatives 5-(4-methoxy-phenyl)-thiazole-2-carboxylic acid pyridin-2-ylmethylene-hydrazide (2-MTPH), 5-(4-methoxy-phenyl)-thiazole-2-carboxylic acid pyridin-3-ylmethylene-hydrazide (3-MTPH), and 5-(4-methoxy-phenyl)-thiazole-2-carboxylic acid pyridin-4-ylmethylene-hydrazide (4-MTPH) were synthesized and characterized. Corrosion inhibition performance of the prepared compounds on mild steel in 0.5 M HCl was studied using gravimetric, potentiodynamic polarisation, and electrochemical impedance techniques. Inhibition efficiency has direct relation with concentration and inverse relation with temperature. Thermodynamic parameters for dissolution and adsorption process were evaluated. Polarisation study reveals that compounds act as both anodic and cathodic inhibitors with emphasis on the former. Impedance study shows that decrease in charge transfer resistance is responsible for effective protection of steel surface by inhibitors. The film formed on the mild steel was investigated using FTIR, SEM, and EDX spectroscopy. Quantum chemical parameters likeEHOMO,ELUMO,ΔE, hardness, softness, and ionisation potential were calculated. Higher value ofEHOMOand lower value ofΔEindicate the better inhibition efficiency of the compounds. Lower ionisation potential of inhibitors indicates higher reactivity and lower chemical stability.