Estimated Electron Affinities Research Articles

Application of an A-A'-A-Containing Acceptor Polymer in Sequentially Deposited All-Polymer Solar Cells.

PNNT has been prepared as a polymeric electron acceptor for organic solar cells. The polymer has an A-A'-A acceptor motif linked alternatively with thiophene and vinyl moieties. The A'-unit is a naphthalene diimide, while the A groups are thiazoles. PNNT films were found to have an estimated electron affinity of ≈4.3 eV and an electron mobility of the order of 10-4 cm2 V-1 s-1. Its relatively low solubility in common chlorinated solvents at ambient temperature allowed the manufacture of sequentially deposited (SD) devices, which were found to have significantly higher efficiency than that of bulk heterojunction (BHJ) solar cells containing the same materials. Grazing-incidence wide-angle X-ray scattering measurements indicated that the SD films retained the ordering of the individual polymers to a greater extent compared to the BHJ films. The best SD devices were found to have a power conversion efficiency of up to 4.5%, with stable performance under thermal stress.

Simple method for determining fullerene negative ion formation

A robust potential wherein is embedded the crucial core-polarization interaction is used in the Regge-pole methodology to calculate low-energy electron elastic scattering total cross section for the C60 fullerene in the electron impact energy range 0.02 ≤ E ≤ 10.0 eV. The energy position of the characteristic dramatically sharp resonance appearing at the second Ramsauer–Townsend minimum of the total cross section representing stable C60− fullerene negative ion formation agrees excellently with the measured electron affinity of C60 [Huang et al., J. Chem. Phys. 140, 224315 (2014)]. The benchmarked potential and the Regge-pole methodology are then used to calculate electron elastic scattering total cross sections for selected fullerenes, from C54 through C240. The total cross sections are found to be characterized generally by Ramsauer–Townsend minima, shape resonances and dramatically sharp resonances representing long-lived states of fullerene negative ion formation. For the total cross sections of C70, C76, C78, and C84 the agreement between the energy positions of the very sharp resonances and the measured electron affinities is outstanding. Additionally, we compare our extracted energy positions of the resultant fullerene anions from our calculated total cross sections of the C86, C90 and C92 fullerenes with the estimated electron affinities ≥3.0 eV by the experiment [Boltalina et al., Rapid Commun. Mass Spectrom. 7, 1009 (1993)]. Resonance energy positions of other fullerenes, including C180 and C240 are also obtained. Most of the total cross sections presented in this paper are the first and only; our novel approach is general and should be applicable to other fullerenes as well and complex heavy atoms, such as the lanthanide atoms. We conclude with a remark on the catalytic properties of the fullerenes through their negative ions.

Photoelectron spectroscopy of nitromethane anion clusters

Nitromethane anion and nitromethane dimer, trimer, and hydrated cluster anions were studied by photoelectron spectroscopy. Vertical detachment energies, estimated electron affinities, and solvation energies were obtained from the photoelectron spectra. Cluster structures were investigated using theoretical calculations. Predicted detachment energies agreed with experiment. Calculations show water binds to nitromethane anion through two hydrogen bonds. The dimer has a non-linear structure with a single ionic CH⋯O hydrogen bond. The trimer has two different solvent interactions, but both involve the weak CH⋯O hydrogen bond.

The synthesis, photophysical and electrochemical properties of a series of novel 3,8,13-substituted triindole derivatives

The synthesis and properties of a series of new 3,8,13-substituted triindole derivatives 1a–1e are reported. The 3,8,13-substituted triindoles were thermally robust with high decomposition temperatures (≥405 °C) and high melt transitions (219 °C–373 °C). Compound 5e was crystallized in the monoclinic system with the space group P21/n. These compounds showed UV–Vis absorption (λmaxAbs) in the range of 311–345 nm in DCM solution and 371–391 nm in solid state, and fluorescence maxima (λmaxEm) in the range of 394–412 nm in DCM solution and 416–461 nm in solid state. The fluorescence quantum yields ranged from 0.27 to 0.58. The estimated electron affinities (LUMO levels) and estimated ionization potential (HOMO levels) of compounds 1a–1e are 3.54–3.71 eV and 5.12–5.48 eV, respectively. Quantum chemical calculations using DFT B3LYP/6-31G showed nearly identical LUMO (−0.72 to −1.10 eV) and HOMO (−4.65 to −4.84 eV) values. These results demonstrated that the new 3,8,13-substituted triindoles are promising thermally stable host materials for organic light-emitting diodes with reasonable hole mobility.

Novel multifunctional organic semiconductor materials based on 4,8-substituted 1,5-naphthyridine: synthesis, single crystal structures, opto-electrical properties and quantum chemistry calculation

A series of 4,8-substituted 1,5-naphthyridines (1a-1h) have been successfully synthesised by a Suzuki cross-coupling between 4,8-dibromo-1,5-naphthyridine (4) and the corresponding boronic acids (2a-2h) in the presence of catalytic palladium acetate in yields of 41.4-75.8% and have ben well characterized. They are thermally robust with high phase transition temperatures (above 186 °C). Compounds 1b, 1e and 1f crystallized in the monoclinic crystal system with the space groups P2(1)/c, P2(1)/c and P2(1)/n, respectively. All of them show the lowest energy absorption bands (λ(max)(Abs): 294-320 nm), revealing low optical band gaps (2.77-3.79 eV). These materials emit blue fluorescence with λ(max)(Em) ranging from 434-521 nm in dilute solution in dichloromethane and 400-501 nm in the solid state. 4,8-Substituted 1,5-naphthyridines 1a-1h have estimated electron affinities (EA) of (2.38-2.72 eV) suitable for electron-transport materials and ionization potentials (IP) of 4.85-5.04 eV facilitate excellent hole-injecting/hole-transport materials properties. Quantum chemical calculations using DFT B3LYP/6-31G* showed nearly identical the lowest unoccupied molecular orbitals (LUMO) of -2.39 to -2.19 eV and the highest occupied molecular orbitals (HOMO) of -5.33 to -6.84 eV. These results demonstrate the 4,8-substituted 1,5-naphthyridines 1a-1h with a simple architecture might be promising blue-emitting (or blue-green-emitting) materials, electron-transport materials and hole-injecting/hole-transport materials for applications for developing high-efficiency OLEDs.

The synthesis, crystal structures and photophysical properties of a series of novel 4,6-diphenyl-1,9-anthrazolines

The synthesis and properties of a series of nine new 4,6-diphenyl-1,9-anthrazolines molecules 1a–1i are reported. Compounds 1a–1i were synthesized by Friedländer condensation of 4,6-dibenzoyl-1,3-phenylenediamines and acetyl-functionalized compounds in the presence of polyphosphoric acid as catalyst, in yields ranging from 60% to 94%. The 4,6-diphenyl-1,9-anthrazolines are thermally robust with high decomposition temperatures (>371.0 °C) and high melt transitions (215.1–322.8 °C). Compounds 1a and 1f crystallized in the triclinic system with the space groups P-1. All of them show the lowest energy absorption bands ( λ max Abs: 397–454 nm), revealing low optical band gaps (2.55–3.00 eV). The compounds emit blue fluorescence with λ max Em ranging from 432 to 493 nm in dilute toluene solution. 4,6-Diphenyl-1,9-anthrazolines 1a–1i have a formal reduction potential in the range −1.02 to −1.19 V (versus SCE) and estimated electron affinities (LUMO levels) of 3.21–3.38 eV. These results demonstrate that the new 4,6-diphenyl-1,9-anthrazolines are promising thermally stable n-type semiconductors for organic electronics.

Novel n-Type Conjugated Ladder Heteroarenes: Synthesis, Self-Assembly of Nanowires, Electron Transport, and Electroluminescence of Bisindenoanthrazolines

A novel π-conjugated heptacyclic framework has been synthesized via a new one-step cyclization that results in a new class of n-type organic semiconductors. Single-crystal structures of bisindenoanthrazolines DADF and DADK showed that the π-conjugated heptacyclic framework is planar and leads to a slipped face-to-face π-stacking with short intramolecular distances (3.39 Å and 3.56 Å, respectively). The series of bisindenoanthrazolines have a formal reduction potential of −0.68 to −0.70 V (vs SCE) and an estimated electron affinity (LUMO level) of 3.65−3.72 eV. Electron mobility in evaporated thin films of the bisindenoanthrazolines, measured by the space-charge limited current method, was as high as 3.84 × 10−4 cm2/(V s) under ambient air conditions. Organic light-emitting diodes based on DADA as the emissive material gave the best performance among the four molecules with a maximum brightness of 7610 cd/m2, and maximum efficiency of 6.6 cd/A with EQE of 2.0% at a brightness of 936 cd/m2. Phosphorescent organic light emitting diodes with fac-tris(2-phenylpyridine)iridium (Ir(ppy)3) as the green triplet emitter and a bisindenoanthrazoline as the electron transport layer showed a brightness of 62 000 cd/m2 and luminous efficiency of 39.2 cd/A at a brightness of 4270 cd/m2. Nanowires of DADF and DADK self-assembled from solution were found to be single-crystalline and their morphology was further investigated by electron microscopy techniques. These results demonstrate the potential of bisindenoanthrazolines as new n-type semiconductors for organic electronics and optoelectronics.

Synthesis and photophysical properties of a series of thermally stable terphenyl-bridged bisbenzimidazoles

Nine novel terphenyl-bridged bisbenzimidazoles were synthesized in high yield by the condensation of o-phenylenediamines and terphenyl dinitriles in the presence of polyphosphoric acid. The bisbenzimidazoles are thermally robust with high decomposition temperatures (>346 °C) and high melting transitions and emit blue light at ∼410 nm with fluorescence quantum yield >0.4 in solution. Electrochemical studies indicate that the novel bisbenzimidazoles have a formal reduction potential in the range of −1.44 to −1.55 V and estimated electron affinities (lowest unoccupied molecular orbital levels) of 3.09–3.24 eV. The results indicate their potential use as blue-emitting materials in organic light-emitting diodes.

Franck–Condon simulation of the photoelectron spectrum of AsF2 and the photodetachment spectrum of AsF2− using ab initio calculations: Ionization energy and electron affinity of AsF2

RCCSD(T) and/or CASSCF/MRCI calculations were carried out on the X(2)B(1) state of AsF(2), the X(1)A(1), ã(3)B(1) and A(1)B(1) states of AsF(2)(+), and the X(1)A(1) state of AsF(2)(-) employing the fully-relativistic small-core effective core potential (ECP10MDF) for As and basis sets of up to augmented correlation-consistent polarized valence quintuple-zeta (aug-cc-pV5Z) quality. Minimum-energy geometrical parameters and relative electronic energies were evaluated, including contributions from extrapolation to the complete basis set limit and from outer core correlation of the As 3d(10) electrons. In addition, simplified, explicitly correlated RHF/UCCSD(T)-F12x calculations were also performed employing different atomic orbital basis sets, and associated complementary auxiliary and density-fitting basis sets. The best theoretical estimates of the adiabatic ionization energies (AIE(0)) of AsF(2)(X(2)B(1)) to the X(1)A(1) and ã(3)B(1) states of AsF(2)(+), including corrections for zero-point vibrational energy (DeltaZPE), are 9.099(8) and 13.290(22) eV respectively. The best estimated electron affinity (EA(0)) of AsF(2) is 1.182(16) eV, also including Delta(ZPE). These are currently the most reliable AIE(0) and EA(0) values for AsF(2). Potential energy functions (PEFs) of the X(2)B(1) state of AsF(2), the X(1)A(1) and ã(3)B(1) states of AsF(2)(+) and X(1)A(1) state of AsF(2)(-) were computed at RCCSD(T)/aug-cc-pV5Z, RCCSD(T)/aug-cc-pCV5Z and RHF/UCCSD(T)-F12a/aug-cc-pCVTZ levels. These PEFs were employed in variational calculations of anharmonic vibrational wavefunctions, which were then utilised to calculate Franck-Condon factors (FCFs), using a method which includes allowance for anharmonicity and Duschinsky rotation. The computed FCFs were used to simulate the first two bands in the photoelectron spectrum of AsF(2) and the first band in the photodetachment spectrum of AsF(2)(-), both yet to be recorded. The simulated spectra obtained using different sets of PEFs were found to be almost identical, suggesting that the simplified explicitly correlated UCCSD(T)-F12x method with a relatively small basis set can be a reliable alternative to the conventional RCCSD(T) correlation methods with a relatively large basis set, but at a significantly lower cost.

Topological Control of Spin States in Disjoint Diradicals

The meta- and para-bis-allylbenzene radical anions have been generated and investigated using mass spectrometry. The ions are formed by reaction of the corresponding bis-2-propenylbenzenes with atomic oxygen anion. Reactivity of the ions indicates that the ions most likely have a bis-allylbenzene structure. Reaction of the ions with carbon disulfide creates CS(2) adducts, which, upon collision-induced dissociation, decompose to regenerate the bis-allylbenzene anion or carbon disulfide radical anion. The branching ratios for the two products indicate differences in the electronic structures of the neutral bis-allylbenzene diradicals. The difference in branching ratios and corresponding estimated electron affinities is interpreted in terms of different electronic states being formed, with the para diradical a singlet and the meta diradical either a ground-state triplet or a singlet with a very small singlet-triplet splitting. The difference in electron affinities is used to estimate a singlet-triplet splitting of 0.06 eV for the para diradical. The studies show that topology can be used to control the electronic properties of disjoint, tetramethyleneethane (TME)-like diradicals.

Structure, electronics, and interaction of hydrogen and oxygen on diamond surfaces

The atomic geometry and electronic structure of diamond surfaces, both clean and with various hydrogen and oxygen terminations, have been studied using ab initio density-functional-theory calculations. Calculated ionization potentials and estimated electron affinities are presented for the different surfaces, while bulk- and surface-related effects are distinguished. Interaction between hydrogen and oxygen on the technologically important (001) surface is also examined. Structural energies indicate that a hydroxylated (001) surface is favored over an oxygenated surface plus gas-phase hydrogen molecules, although an overestimate in the strength of hydrogen bonding on the $\mathrm{O}\mathrm{H}$-terminated surface might lend it an artificially high stability. A surface terminated with a combination of $\mathrm{O}$, $\mathrm{H}$, and $\mathrm{O}\mathrm{H}$ groups has a structural energy part-way between the extremes of a fully oxygenated and a fully hydroxylated surface. Electronically, while the hydrogenated and oxygenated surfaces respectively show their expected negative and positive (bulk) electron affinities, the $\mathrm{O}\mathrm{H}$-terminated surface and the surface with the aforementioned combination of groups both show small negative electron affinities. However, all surfaces except the combination surface have introduced unoccupied states into the bandgap, which correspond to positive surface electron affinity and could act as traps for electrons that would otherwise escape the material; the implications for band bending are discussed. As expected, the hydrogenated surfaces show by far the lowest ionization potentials, and are therefore the most suitable for exploiting the transfer doping effect, although $\mathrm{O}\mathrm{H}$-terminated surfaces might be successfully transfer doped if an adsorbate molecule of very high electron affinity were to be used.

New n-type organic semiconductors: synthesis, single crystal structures, cyclic voltammetry, photophysics, electron transport, and electroluminescence of a series of diphenylanthrazolines.

The synthesis, properties, and electroluminescent device applications of a series of five new diphenylanthrazoline molecules 1a-1e are reported. Compounds 1b, 1c, and 1d crystallized in the monoclinic system with the space groups P2(1)/c, C2/c, and P2(1)/c, respectively, revealing highly planar molecules. Diphenylanthrazolines 1a-1e have a formal reduction potential in the range -1.39 to -1.58 V (versus SCE) and estimated electron affinities (LUMO levels) of 2.90-3.10 eV. Compounds 1a-1e emit blue light with fluorescence quantum yields of 58-76% in dilute solution, whereas they emit yellow-green light as thin films. The diphenylanthrazoline molecules as the emissive layers in light-emitting diodes gave yellow light with a maximum brightness of 133 cd/m(2) and an external quantum efficiency of up to 0.07% in ambient air. Bilayer light-emitting diodes using compounds 1a-1e as the electron-transport layer and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) as the emissive layer had a maximum external efficiency of 3.1% and 2.0 lm/W and a brightness of up to 965 cd/m(2) in ambient air. These results represent enhancements of up to 50 times in external quantum efficiency and 17 times in brightness when using 1a-1e as the electron-transport materials in polymer light-emitting diodes. These results demonstrate that the new diphenylanthrazolines are promising n-type semiconductors for organic electronics.

MRCI studies on the electronic structure of AlN and AlN −, and the electron affinity of AlN

Using multireference configuration-interaction methods and double to triple-zeta basis sets with semidiffuse and polarization functions, potential energies and spectroscopic constants for low-lying doublet, and quartet states of AlN − were calculated. X 2 Σ + has R e =3.280 bohr and ω e=870 cm −1 . 1 2 Π lies 0.17 eV above the ground state. Using an estimated electron affinity of 2.1 eV for AlN, four states of AlN − are found to be stable, namely X 2 Σ + , 1 2 Π , 2 2 Σ + , and 1 4 Σ + . Comparisons with the isovalent anions BN − (three stable states) and AlP − (seven stable states) are made. Photo-detachment of an electron from the 1 2 Π state of AlN − can lead to an accurate determination of the energy difference between the two close-lying lowest states of AlN, X 3 Π and 1 3 Σ − , predicted here to be 0.09 eV apart.

Electron affinities of polycyclic aromatic hydrocarbons determined by the kinetic method

AbstractThe kinetic method has been applied in the determination of electron affinities (EA) of polycyclic aromatic hydrocarbons (PAHs) using electron attachment desorption chemical ionization mass spectrometry (DCI‐MS) and triple quadrupole tandem mass spectrometry. Electron‐bound dimers of PAHs (viz. solvated radical anions) are generated in the ion source and they fragment competitively upon collisional activation to yield the intact monomeric molecular radical anions. The ratio of the abundances of these two ions reflects the difference in electron affinities of the PAHs. Relative electron affinities are ordered as phenanthrene < perylene < 1,2‐benzanthracene < benzo [ghi] perylene < anthracene < pyrene < fluoranthene < biphenylene on the basis of multiple pairwise measurements. On the assumption that the effective temperature of the electron‐bound dimers is constant, under fixed desorption conditions, and using phenanthrene (EA = 0.307 eV), anthracene (EA = 0.556 eV), pyrene (EA = 0.591 eV) and fluoranthene (EA = 0.63 eV) as reference compounds, the electron affinities of several PAHs are estimated as perylene (0.35 eV), 1,2‐benzanthracene (0.39 eV), benzo [ghi] perylene (0.42 eV) and biphenylene (0.89 eV). The calculated effective temperature using the known EAs of the reference compounds, phenanthrene, anthracene, pyrene and fluoranthene, is 1251 K. The high effective temperature in the electron‐bound dimer is ascribed to both the weak binding in the electron‐bound dimer and to the choice of ionization conditions. The same methodology was applied to estimate the electron affinities of substituted PAHs. For alkyl‐substituted PAHs, e.g. 1‐methylanthracene, the estimated electron affinity (0.55 ± 0.10 eV) is consistent with electron transfer equilibrium studies. However, for halogenated PAHs, the ratio of fragment ion abundances does not correlate with the known electron affinity difference when a PAH and a halogenated PAH comprise the electron‐bound dimer. This is suggested to be due to differences in the structures of the cluster ions generated upon halogen substitution. The expected affinity results are obtained when the electron‐bound dimer is comprised of two halogenated PAHs. Estimated electron affinity values for 1‐bromopyrene (0.72 ± 0.10 eV) and 9‐bromoanthracene (0.61 ± 0.10 eV) are slightly higher than the electron affinities of pyrene and anthracene, respectively.

Electron affinities of BH, B 2, BC and BN molecules determined using charge inversion spectrometry

The anions BH −, B − 2, BC − and BN − have been observed as products of charge-inversion reactions of the respective cations formed from BH 3, B 2H 6, B(OCH 3) 3 and BH 3NH 3. The spectra, recorded using CS 2 target gas, have forms which are consistent with documented ab initio energies and equilibrium bond lengths determined for these anions. In particular, given the theoretical ionisation energies, the spectra establish the electron affinities for BH and BN, and average electron-attachment energies for B 2 and BC (where multiple bound anionic states are populated) as being 0.30 ± 0.25, 2.9 ± 0.3, 1.3 ± 0.4, (1.8 eV estimated electron affinity) and 2.4 ± 0.3 eV, (2.8 eV estimated electron affinity) respectively. The spectrum of B +/CS 2 is also discussed.

Electron affinities of alkaline-earth and actinide elements calculated with the local-spin-density-functional theory.

The generalized exchange local-spin-density-functional theory with self-interaction correction and correction of the statistical exchange potential was used to calculate the electron affinities of alkaline-earth and actinide elements. The effect of relativistic correction by the mass velocity and Darwin terms and correlation correction on the electron affinities is discussed. The calculation of the negative ions shows that, although the correlation correction to the potential is very small, it is essential for obtaining converged values for most of the negative ions. The calculated results predict stable negative ions for the alkaline-earth elements Ca, Sr, Ba, and Ra, supporting the calculations of Vosko et al. [Phys. Rev. A 39, 446 (1989)] and Fischer [Phys. Rev. Lett. 59, 2263 (1987); Phys. Rev. A 39, 963 (1989)]. Estimated electron affinities for the actinide elements are given.

Composition of Some Conducting Complexes of 1,6-Diaminopyrene

The absorption spectra of solid complexes of 1,6-diaminopyrene with quinones exhibiting high electrical conductivity show them to be mostly radical-ion salts. The mole fractions of ionic component for complexes with bromanil, chloranil, and 2,3-dichloro-5,6-dicyano-benzoquinone are 0.65, 0.90, and 0.95, respectively. This is the order of the estimated electron affinities of the acceptors but not of the conductivity of the complexes. The iodanil complex, with much higher resistivity, shows little ionic component.

Estimated Electron Affinities of the Light Elements

The electron affinities of the light elements have been estimated by an empirical method of extrapolation. The ionization potentials ($I$) of isoelectronic systems are considered to be parabolic functions of the atomic number ($Z$). The Moseley curves ${I}^{\frac{1}{2}}:Z$ of the first ionization potential of the electronic systems containing from one to eighteen electrons have been completed. They are nearly straight lines except in their lower extremities where they show a bending towards the axis of atomic number $Z$. Wherever a check was possible it is found that the estimated electron affinities agree with experiment or with other calculation as obtained from wave mechanics or from thermochemical considerations by means of a Born-Haber cycle. The estimated electron affinities (in electron-volts) are: H (+0.7), He (-0.5), Li (+0.3), Be (-0.6), B (+0.1), C (+1.37), N (+0.04), O (+3.8), F (+3.9), Ne (-1.20), Na (+0.1), Mg (-0.9), Al (-0.2), Si (+0.6), P (+0.2), S (+2.1), Cl (+3.7), A (-1.0), Ni (+0.3), Cu (+1.2), Ag (+1.0), Hg (+1.8).