Adiabatic Ionization Potentials Research Articles

One-electron oxidation of ds(5'-GGG-3') and ds(5'-G(8OG)G-3') and the nature of hole distribution: a density functional theory (DFT) study.

Of particular interest in radiation-induced charge transfer processes in DNA is the extent of hole localization immediately after ionization and subsequent relaxation. To address this, we considered double stranded oligomers containing guanine (G) and 8-oxoguanine (8OG), i.e., ds(5'-GGG-3') and ds(5'-G8OGG-3') in B-DNA conformation. Using DFT, we calculated a variety of properties, viz., vertical and adiabatic ionization potentials, spin density distributions in oxidized stacks, solvent and solute reorganization energies and one-electron oxidation potential (E0) in the aqueous phase. Calculations for the vertical state of the -GGG- cation radical showed that the spin was found mainly (67%) on the middle G. However, upon relaxation to the adiabatic -GGG- cation radical, the spin localized (96%) on the 5'-G, as observed in experiments. Hole localizations on the middle G and 3'-G were higher in energy by 0.5 kcal mol-1 and 0.4 kcal mol-1, respectively, than that of 5'-G. In the -G8OGG- cation radical, the spin localized only on the 8OG in both vertical and adiabatic states. The calculated vertical ionization potentials of -GGG- and -G8OGG- stacks were found to be lower than that of the vertical ionization potential of a single G in DNA. The calculated E0 values of -GGG- and -G8OGG- stacks are 1.15 and 0.90 V, respectively, which owing to stacking effects are substantially lower than the corresponding experimental E0 values of their monomers (1.49 and 1.18 V, respectively). SOMO to HOMO level switching is observed in these oxidized stacks. Consequently, our calculations predict that local double oxidations in DNA will form triplet diradical states, which are especially significant for high LET radiations.

A stable, highly oxidizing radical cation

Changes in adiabatic ionization potential and half wave oxidation potential withorthoandparasubstitution on anN-alkylated phenothiazine.

Tuning of optoelectronic and charge transport properties of D–π–A diketopyrrolopyrrole-triphenylamine derivatives for organic solar cells application

A series of D–π–A diketopyrrolopyrrole-triphenylamine-based molecules have been designed for organic solar cells (OSCs) applications. Their optical, electronic, and charge transport properties have been systematically investigated by applying density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. It turned out that the vertical electronic transitions are characterized as intramolecular charge transfer. The calculated results show that the energetic driving force (ΔEL-L), adiabatic ionization potential (IPa), adiabatic electron affinity (EAa), and absorption spectrum can be tuned effectively by the introduction of different conjugate π-bridges. The designed molecules can serve as donor materials with smaller band gaps and intense absorption spectra, which is favourable for improving the efficiency of OSCs. Our results suggest that the designed molecules can provide match well with the typical fullerene acceptors PC61BM, bisPC61BM, and PC71BM. In addition, the designed molecules can be used as promising both eletron and/or hole transport materials. Furthermore, the different conjugate π-bridges do not significantly affect the stability of these molecules.

In silico design of hydrazone antioxidants and analysis of their free radical-scavenging mechanism by thermodynamic studies

BackgroundAntioxidants are very crucial in maintaining the normal function of body cells, as they scavenge excess free radical in the body. A set of hydrazone antioxidants was designed by in silico screening. The density functional theory (DFT) method was employed to explore the reaction energetics of their free radical-scavenging mechanism. With the aid of the developed quantitative structure-activity relationship (QSAR) model for hydrazone antioxidants, the structure and antioxidant activity of these compounds were predicted. Three potential reaction mechanisms were investigated, namely, hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET). Bond dissociation enthalpy (BDE), adiabatic ionization potential (AIP), proton dissociation enthalpy (PDE), proton affinity (PA), electron transfer enthalpy (ETE) and Gibbs free energy that characterize the various steps in these mechanisms were calculated in the gas phase.ResultsA total of 25 hydrazone antioxidants were designed, in which the molecule MHD 017 gave the best antioxidant activity. Among the tested molecules, MHD 017 at the 10-OH site gave the best results for the various thermodynamic parameters calculated. The reaction Gibbs free energy results also indicate that this is the most favoured site for free radical scavenge.ConclusionThe obtained results show that HAT and SPLET mechanisms are the thermodynamically plausible reaction pathways of free radical scavenge by hydrazone antioxidants. The reactivity of these compounds towards the hydroperoxyl radical (HOO·) was greater than that towards the methyl peroxyl radical (CH3OO·) based on the exergonicity of the calculated reaction Gibbs free energy.Graphical abstract

Structures and Energetics of Neutral and Cationic Pyrene Clusters.

The low energy structures of neutral and cationic pyrene clusters containing up to seven molecules are searched through a global exploration scheme combining parallel tempering Monte Carlo algorithm and local quenches. The potential energies are computed at the density functional based tight binding level for neutrals and configuration interaction density functional based tight binding for cations in order to treat properly the charge resonance. New simplified versions of these schemes are also presented and used during the global exploration. Neutral clusters are shown to be made of compact assemblies of sub-blocs containing up to three units whereas cations present a charged dimer or trimer core surrounded by neutral units. The structural features of the clusters are analyzed and correlated for the cation with the charge distribution. The stability of clusters is also discussed in terms of cohesive and evaporation energies. Adiabatic and vertical ionization potentials are also discussed.

Kinetics and Mechanism of the Antioxidant Activities of C. olitorius and V. amygdalina by Spectrophotometric and DFT Methods.

The kinetics and mechanism of the antioxidant activities of the methanolic extract of the leaves of two vegetables [Corchorus olitorius (C. olitorius) and Vernonia amygdalina (V. amygdalina)] have been studied using experimental and theoretical approaches. The kinetics (second order and pseudo-first order) of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities of the leaf extracts at varying times (30–90 min) were determined using the UV–visible spectrophotometry method at λmax = 517 nm, whereas the mechanism was studied by density functional theory at two levels of functionals (B3LYP and LC-ωPBE) using bond dissociation enthalpy and adiabatic ionization potential values. Molecular properties such as the highest occupied molecular orbital, lowest unoccupied molecular orbital, electronegativity (χ), electrophilicity (ω), hardness (η), and softness (S) of the predominant phenolic antioxidants were also compared. The second-order kinetics is favored by both plants rather than pseudo-first order; however, V. amygdalina with a second-order rate constant k2 of 0.0152 (mM)−1 min–1 is faster in scavenging DPPH radicals than C. olitorius with a k2 value of 0.0093 (mM)−1min–1. Chlorogenic acid and luteolin-7-O-β-glucuronide, which are the most abundant phenolic acid antioxidant in C. olitorius and V. amygdalina, both preferably scavenge the DPPH radical via a hydrogen atom transfer mechanism. This is evident from their lower bond dissociation enthalpy values than the adiabatic ionization potential values. Successful molecular docking of these phenolic compounds indicates that both compounds form favorable interactions with the therapeutic target, xanthine oxidase.

Exploring the opto-electronic and charge transfer nature of F-BODIPY derivatives at molecular level: A theoretical perspective

The goal of current work is to investigate the effect of ethyl group on the electronic, photo-physical and charge transport properties of F-BODIPY, which has been explored at the molecular level after substituting ethyl group at two position of F-BODIPY molecule. In current study; optical, electronic and charge transfer properties for F-BODIPY derivatives (Comp_1, Comp_2 and Comp_3) have been theoretically investigated. All the molecules have been optimized at the ground (S0) and first excited (S1) states using density functional theory (DFT) and time dependent DFT (TD- DFT) with the hybrid functional/basis set (B3LYP /6-31G**), respectively. Effect of ethyl groups at two different positions on the electronic, optical and charge transport properties of 5,5-difluoro-1,37,9-tetramethyloctahydro-1H,5H-514-dipyrrolo[1,2-c:2′,1′-f] [1–3] diazaborinine (Comp_1) as parent molecule has been studied at molecular level. The introduction of ethyl at two positions in Comp_1 led to a red shifted absorption spectra in comparison with parent molecule in the violet region. Various properties of interest such as highest occupied molecular orbitals (HOMO), lowest unoccupied molecular orbitals (LUMO), vertical electron affinity (EAv), adiabatic electron affinity (EAa), vertical ionization potential (IPv), adiabatic ionization potential (IPa), electron reorganization energies (λe) and hole reorganization energies (λh) were explored. Additionally, global reactivity descriptors e.g. electronic chemical potential (μ), electronegativity (χ), Electrophilicity (ω), hardness (η), softness (S) and electrophilicity index (ωi) have been calculated theoretically.

Theoretical Studies on Novel Gridspiroarenes: Structures, Noncovalent Interactions and Reorganization Energies

Summary of main observation and conclusionOrganic semiconductor materials with low reorganization energy have various applications such as in organic light‐emitting diodes (OLEDs), organic field‐effect transistor (OFETs) and organic solar cells (OSCs). In this work, we have designed a new class of gridspiroarenes (GS‐SFX and GS‐SITF) with #‐shaped structures, which have novel crisscross geometrical structures compared to widely used spirocyclic arenes—SFX and SITF. The structure electronic properties, adiabatic ionization potentials (IPa), adiabatic electron affinities (EAa) and reorganization energies (λ) of GS‐SFX and GS‐SITF have been calculated using density functional theory (DFT) method. The calculated HOMO and LUMO spatial distributions suggest that GS‐SFX and GS‐SITF have better transport properties. The noncovalent interaction analysis shows the weak intramolecular interactions between their arms. The results indicate that the reorganization energies of GS‐SFX and GS‐SITF are significantly reduced compared to the dimer structures—DSFX and DSITF. Furthermore, the GS‐SITF1 which is one of the isomers of GS‐SITF exhibits the lowest values for λ(h) (0.067 eV) and λ(e) (0.153 eV). Therefore, we believe the predicted structure, electronic property, and reorganization energy are good indicator for transport materials. This work has systematically studied the effect of gridization, which provides insights to design organic semiconductor materials with excellent charge transport properties.

Record Low Ionization Potentials of Alkali Metal Complexes with Crown Ethers and Cryptands.

Electronic properties of series of alkali metals complexes with crown ethers and cryptands were studied via DFT hybrid functionals. For [M([2.2.2]crypt)] (M=Li, Na, K) extremely low (1.70-1.52 eV) adiabatic ionization potentials were found. Such low values of ionization energies are significantly lower than those of alkali metal atoms. Thus, the investigated complexes can be defined as superalkalis. As a result, our investigation opens up new directions in the designing of chemical species with record low ionization potentials and extends the explanation of the ability of the cryptates and alkali crown ether complexes to stabilize multiple charged Zintl ions.

Vibronic structure of the cyanobutadiyne cation. I. VUV photoionization study of HC5N.

We report the vacuum-ultraviolet threshold-photoelectron spectrum of HC5N recorded over a wide spectral range, from 84 000 to 120 000 cm-1, with a 120 cm-1 spectral resolution, better than what was achieved in previous photoelectron studies, and with mass selectivity. The adiabatic ionization potential of cyanobutadiyne is measured at 85 366 (±40) cm-1. Assignment of the vibrational bands of the four lowest electronic states X+2Π, A+2Π, B+2Σ+, and C+2Π are performed, supported by high level ab initio calculations which are fully detailed in Paper II [B. Gans et al., J. Chem. Phys. 150, 244303 (2019)] and by Franck-Condon simulations. Only vibrational stretching modes are observed in the threshold-photoelectron spectra. The ground state of HC5N+ exhibits a vibrational progression in the ν2 stretching mode involving mainly the elongation of the C≡C triple bonds, whereas the A+ and C+ excited electronic states show a progression in the stretching mode mainly associated with the elongation of the C≡N bond, i.e., ν4 and ν3, respectively. The B+ state appears almost as a vibrationless structure in close vicinity to the A+ state.

Density Functional Theory Calculations of Geometrical and Electronic Properties of Neutral and Charged Silicon Oxide Clusters

We investigate neutral and charged silicon oxide clusters (Si nO n, n = 1–7) using density functional theory (DFT) calculations. For searching a local minimum structure of neutral, cationic, and anionic silicon oxide clusters, ab initio Monte Carlo (MC) simulations are used. Local minimum structures founded from simulations are again calculated using DFT calculations to find a global minimum structure. Relative energies based on total energy differences between the most stable structure and the possible isomers obtained from the calculation are reported. For studying structural properties of silicon oxide clusters, the PBE functional is used with DGDZVP and CEP‐121G* basis sets. These basis sets are compared with each other and with the DGDZVP and 6–311 + G* basis sets, which are also compared with each other in terms of their electronic properties. Thus, the PBE/DGDZVP model is the best choice for large silicon oxide clusters calculations. Examinations are performed on the SiO distances, Si‐O‐Si average bond angles, atomization energies per atom, second difference in energies, HOMO–LUMO gaps, adiabatic ionization potentials, and adiabatic electron affinities. All calculations use Gaussian09 program.

Optoelectronic properties of benzotrithiophene isomers: A density functional theory study

Benzotrithiophene (BTT) isomers were investigated using density functional theory (DFT) and time‐dependent DFT (TD‐DFT) with the aim to explore their structures, linear optical properties, vertical and adiabatic ionization potentials (IPv and IPa), electron affinities (EAv and EAa), and reorganization energies (λ). The computed bond lengths and bond angles at the B3LYP/6–311+G (d, p) level of theory are in good agreement with experimental crystal structures of the known BTTs. These molecules are planar with zero dihedral angle, making them an ideal backbone for high charge mobility. The UV–visible spectra of BTT isomers are in the range 280–360 nm. All BTT isomers have low hole/electron reorganization energies, which is the main characteristic of good hole/electron transporting materials, and these isomers in turn have potential applications in the field of organic materials.

Radical Scavenging Activity of Natural-Based Cassaine Diterpenoid Amides and Amines.

The radical scavenging capacities of four new cassaine diterpenoid amides including 3β-hydroxydinorerythrosuamide (1), 3β-acetoxydinorerythrosuamide (2), 3β-tigloyloxydinorerythrosuamide (3), and 6α-hydroxydinorcassamide (4) present in leaf extract and four new cassaine diterpenoid amines namely erythroformine A (5), erythroformine B (6), 6α-hydroxy-nor-cassamine (7), and nor-erythrosuamine (8) recently identified in the extract of the bark of Erythrophleum fordii were elucidated using density functional theory (DFT) method. Different thermochemical properties characterizing antioxidant potential including bond dissociation enthalpy (BDE), proton affinity (PA), and adiabatic ionization potential (IP) were calculated at the B3LYP/6-311G(d,p) level of theory. Scavenging reaction mechanisms of cassaine diterpenes toward HOO• radical including formal hydrogen transfer (FHT; either hydrogen atom transfer (HAT) or proton coupled electron transfer (PCET)), radical adduct formation (RAF), single electron transfer (SET), and proton transfer (PT) were studied in the gas phase, water, and benzene. The potential energy profiles and kinetic calculations for the FHT and RAF reactions were calculated at 298.15 K. The results showed that all the studied compounds present strong antioxidant activity via HAT mechanism with BDEs varying from 69.4 to 77.9 kcal/mol. While solvents have only a slight effect on HAT and RAF mechanisms, SET and PT reactions are likely to occur in polar media. Among the studied compounds, 3 is the most reactive one both for HAT (H-abstraction at C7, Δ H -11.3 kcal/mol) and for RAF (radical addition at C13 = C15 bond, Δ H -5.2 kcal/mol) reactions. The rate constants of these reactions are also comparable with several referenced antioxidants such as Trolox and ascorbic acid.

New types of organic semiconductors based on diketopyrrolopyrroles and 2,1,3-benzochalcogenadiazoles: a computational study.

A comprehensive computational study is performed on model compounds based on 2,1,3-benzochalcogenadiazoles and diketopyrrolopyrroles of A-π-A'-π-A architecture (A and A' represent 2,1,3-benzochalcogenadiazoles and diketopyrrolopyrroles, respectively, and π is the bridging unit between them including thiophene, furan, and selenophene) for their utility as organic semiconductors. The compounds were found to possess planar geometry, which is a desired property for organic semiconductors. The electronic properties, including adiabatic and vertical electron affinity (EA), adiabatic and vertical ionization potential (IP), reorganization energy (λ), hole injection barrier and electron injection barrier, transfer integral, and charge mobility, were calculated. The electron affinity is higher in the case of thiophene/selenophene as the linker for a given terminal benzochalcogenadiazole than the corresponding compounds with furan as a linker, while the ionization potential is lowest for compounds having selenophene as the linker with a given terminal benzochalcogenadiazole moiety than the compounds having furan or thiophene as a linker. The hole injection barrier in these compounds is lower than the electron injection barrier, which facilitates the hole injection from the metal electrode, while hole reorganization energy is found to be larger than the electron reorganization energy. The compounds possess hole mobilities in the range of 2.50-4.91cm2/Vs and electron mobilities in a similar range of 4.58-9.68cm2/Vs. This study reveals that compounds based on a combination of diketopyrrolopyrrole and 2,1,3-benzochalcogenadiazole units would exhibit hole transporting properties and act as potential ambipolar materials.

Structures and binding energies for complexations of different spin states of Ni+ and Ni2+ to aromatic molecules

Density functional theory calculations, using the B3LYP parameterisation, were performed to determine structures, vibrational frequencies, and binding energies for complexation of Ni+ and Ni2+ cations with benzene and naphthalene molecules and clusters. The calculations employed the Stuttgart basis set with ECP pseudo potentials for the Ni cations and basis sets of at least triple ζ plus polarisation, and diffuse quality for C and H. The effect of electron correlation on non-bonded interactions was accounted for by the Grimme GD3 dispersion correction. Counterpoise computations were made for BSSE. Comparison between experiment and theory provide fascinating new insight into the bonding for these prototypical organometallic (OM) complexes. These structures have a sandwich topology, indicating major structural reorganisations occuring when benzene or naphthalene interact with Ni cations. Adiabatic electron affinities and ionisation potentials agree well with experiment when available. Binding energies were also determined, providing insight into the stability of the complexes. The results presented here provide important information for future studies to address additional investigations of both problems of the electronic structure properties of these complexes, as well as the role of the polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium (ISM) and soot formation in combustion. The Ni+/Ni2+ + aromatic organometallic bonding is of the same order of stability as an aromatic C–H bond. Such bonding modifies the IR spectrum of the complexed aromatic molecules by enhancing the 3.3 μm feature and decreasing the C–H bands in the 11–12 μm range (γ C–H). Organometallic complexation reactions may contribute significantly to metal depletion in the ISM.

Unveiling the electronic structures and ligation effect of the superatom-polymeric zirconium oxide clusters: a computational study.

Discovering the non-noble ZrO cluster as an analog of the noble metal catalyst Pd is of significance toward designing functional materials with fine-tuned properties using the superatom concept. The effect of gradually assembling the ZrO superatomic unit on the electronic structures and chemical bonding of larger ZrO-polymeric clusters, however, is unclear. Herein, by using density functional theory (DFT) calculations, the lowest-energy structures and low-lying isomers of the (ZrO)n-/0 (n = 2-5) clusters were optimized, in which every O atom in these clusters tends to connect its adjacent two Zr atoms forming metal oxygen bridge bonds. Insights into the electronic characteristics of these clusters were obtained by analyzing their molecular orbitals (MOs) and density of states (DOS). More importantly, our studies on the CO (electron acceptor) and PH3 (electron donor) ligated Zr3O3 clusters unveil that the ligation process can substantially alter the electronic properties of the clusters by tuning the HOMO and LUMO states, which may have potential applications in photovoltaics. Strikingly, the successive attachment of PH3 on Zr3O3 dramatically lowers the adiabatic ionization potential (AIP) of the ligated clusters, resulting in the formation of stable superalkali clusters with large HOMO-LUMO gaps. Furthermore, the potential of constructing the superalkali Zr3O3(PH3)5 based 1-D cluster assembled material was also examined.

Theoretical Study of the Effect of Simultaneous Doping with Silicon, on Structure and Electronic Properties of Adamantane

In this paper, structural and electronic properties of adamantane (C10H16) and its Si-doped derivatives were calculated using density functional theory. In order to find diamondoids with specific properties, one to ten carbon atoms of adamantane were substituted with silicon atoms and the changes in structural and electronic properties of adamantane after substituting were investigated. HOMO-LUMO energies of 1–10 Si-doped adamantane and their gaps were calculated and the parameters that affect on the energy gaps of Si-doped structures were introduced. Among the doped molecules, 4-Si doped adamantane with high symmetry structure shows distinct properties. Adiabatic electron affinity and ionization potentials were calculated using Gibbs free energies of cationic and anionic forms of all structures. The results show that the electron affinity of adamantane is negative and reduces to positive values by simultaneous C/Si doping in 7–10-sila-doped adamantane. These results show the vacuum level transfer from above to below the conduction band. NBO charge analyses were also applied for describing the electron affinity and Ionization potential results.

Ionization and fragmentation of uracil upon microhydration.

We study at the DFT level the ionization and the fragmentation of uracil in the presence of zero, one and two water molecules, to unravel the effect of microhydration on the reactivity of this nucleobase. We show that the microhydration lowers the adiabatic and vertical ionization potentials by 0.41 eV and 0.22 eV, respectively. Furthermore, microhydration increases the activation energies of the different dissociation channels up to 0.5 eV and restricts the formation of some fragments, in particular those corresponding to the C5-C6 fragmentation pathway. For the first time, our theoretical study shows new transition states and minima not found for the gas phase, hence indicating a change in the fragmentation mechanisms, as well as a stabilizing effect of microhydration, confirming previous experimental studies.

Experimental and theoretical threshold photoelectron spectra of methylene.

The threshold photoelectron spectrum of methylene (CH2), produced by consecutive H atom abstractions on methane, has been recorded using synchrotron radiation. The experimental spectrum spans the region of the X + 2Π u ← X 3 B 1 ionizing transition. It is modeled starting from ab initio bending potentials and using the bending approach introduced by Coudert et al. [J. Chem. Phys. 148, 054302 (2018)] accounting for the quasilinearity of CH2 and the strong Renner-Teller interaction in . This first calculation yields a theoretical threshold photoelectron spectrum which is in moderate agreement with the experimental one. A more accurate approach treating the three vibrational modes is developed for computing the threshold photoelectron spectrum of triatomic molecules. This new treatment is tested modeling the already measured threshold photoelectron spectrum of the X + 2Π u ← X 1 A 1 ionizing transition of the water molecule. The threshold photoelectron spectrum of CH2 computed with the new approach compares more favorably with the experimental spectrum and yields an adiabatic ionization potential of 10.386(6) eV.

Quantum Monte Carlo study of the electron binding energies and aromaticity of small neutral and charged boron clusters.

The valence electron binding energies and the aromaticity of neutral and charged small boron clusters with three and four atoms are investigated using a combination of the fixed-node diffusion quantum Monte Carlo (FN-DMC) method, the density functional theory, and the Hartree-Fock approximation. The obtained electron binding energies such as the adiabatic detachment energy, vertical detachment energy, adiabatic ionization potential, and the vertical ionization potential are in excellent agreement with available experimental measurements. Their decomposition into three physical components such as the electrostatic potential and exchange interaction, the relaxation energy, and the electronic correlation effects has allowed us to determine that the neutral boron clusters are stabilized by the electrostatic and exchange interactions, while the anionic ones are stabilized by the relaxation and correlation effects. The aromaticity is studied based on electronic structure principles descriptor and on the resonance energy. The FN-DMC results from the electronic structure principles of the energy, hardness, and eletrophilicity have supported the aromaticity of , , and B4 and partially supported the aromaticity of the clusters B3, , and . The obtained values for the resonance energy of the clusters , B3, , B4, , and are 55.1(7), 54.2(8), 33.9(7), 84(1), 67(1), and 58(1) kcal/mol, respectively. Therefore, the order of decreasing stability of the trimer is , while for the tetramer it is , which is in agreement with the results from the molecular orbital analysis.