Anionic States Research Articles

Pushing the Length Limit of Dihydrodiboraacenes: Synthesis and Characterizations of Boron‐Embedded Heptacene and Nonacene

AbstractBoron‐embedded heteroacenes (boraacenes) have attracted enormous interest in organic chemistry and materials science. However, extending the skeleton of boraacenes to higher acenes (N≥6) is synthetically challenging because of their limited stability under ambient conditions. Herein, we report the synthesis of boron‐embedded heptacene (DBH) and nonacene (DBN) as the hitherto longest boraacenes. The former is highly stable (even after 240 h in tetrahydrofuran), while the latter is air‐sensitive with the half‐life (t1/2) of 11.8 min. The structures of both compounds are verified by single‐crystal X‐ray diffraction, revealing a linear backbone with an antiaromatic C4B2core. Photophysical characterizations associated with theoretical calculations indicate that both compounds exhibit highly efficient anti‐Kasha emissions. Remarkably, the air‐stableDBHmanifests an ultrahigh photoluminescence quantum yield (PLQY) of 98±2 % and can be chemically reduced to its radical anion and dianion states, implying the value of boron‐doped higher acenes as novel functional materials.

Al13\u2212 and B@Al12\u2212 superatoms on a molecularly decorated substrate

Aluminum nanoclusters (Aln NCs), particularly Al13− (n = 13), exhibit superatomic behavior with interplay between electron shell closure and geometrical packing in an anionic state. To fabricate superatom (SA) assemblies, substrates decorated with organic molecules can facilitate the optimization of cluster–surface interactions, because the molecularly local interactions for SAs govern the electronic properties via molecular complexation. In this study, Aln NCs are soft-landed on organic substrates pre-deposited with n-type fullerene (C60) and p-type hexa-tert-butyl-hexa-peri-hexabenzocoronene (HB-HBC, C66H66), and the electronic states of Aln are characterized by X-ray photoelectron spectroscopy and chemical oxidative measurements. On the C60 substrate, Aln is fixed to be cationic but highly oxidative; however, on the HB-HBC substrate, they are stably fixed as anionic Aln− without any oxidations. The results reveal that the careful selection of organic molecules controls the design of assembled materials containing both Al13− and boron-doped B@Al12− SAs through optimizing the cluster–surface interactions.

Low-Energy Electron Elastic Total Cross Sections for the Large Actinide Atoms Cf, Fm and Md

The rigorous Regge pole method has been used to investigate negative-ion formation in the large actinide atoms Cf, Fm and Md through the elastic total cross sections (TCSs) calculation in the electron impact energy range 0.0 ≤ E ≤ 10.0eV. Ground, metastable and excited negative-ion formation as well as shape resonances (SRs) and Ramsauer-Townsend (R-T) minima are found to characterize generally the TCSs which also exhibit fullerene molecular behavior near threshold through the TCSs of the highest excited states, while maintaining atomic character through the ground state TCSs. Additionally, a polarization-induced metastable TCS with a pronounced SR appears for the first time very close to threshold in the Cf TCSs, having flipped over from a deep R-T minimum near threshold in the Bk TCSs. This behavior manifests the impact of the size effect and the 6d-orbital collapse as well as demonstrates the sensitivity of the R-T minima and the SRs to the electronic structure of these atoms, thereby permitting their first ever use as novel confirmation of Cf as a transitional element in the actinide series. Rigorous and unambiguous ground, metastable and excited anionic states BEs extracted from the TCSs are compared with the existing electron affinities.

Four Dibenzofuran‐Terminated High‐Triplet‐Energy Hole Transporters for High‐Efficiency and Long‐Life Organic Light‐Emitting Devices

The weak stability of a hole-transporter upon approaching the anion state is one of the major bottlenecks for developing long-life organic light-emitting devices (OLEDs). Therefore, in this study, we developed a series of thermally and electrically stable hole-transporters that are end-capped with four dibenzofuran units. These materials exhibit i) high bond dissociation energy (BDE) toward the anion state, ii) a high glass transition temperature (Tg >130 °C), and iii) high triplet energy (ET >2.7 eV), thereby enabling approximately 20 % high external quantum efficiency (EQE) and significantly prolonging the stability of both thermally activated delayed fluorescent (TADF) and phosphorescent OLEDs with an operation lifetime at 50 % (LT50 ) of 20 000-30 000 h at 1000 cd m-2 . In addition, investigating their structure-property relationship revealed that ionization potential (IP ), BDE, and Tg are critical prerequisites for the hole-transporter to prolong lifetime in OLEDs.

Valence-, Dipole- and Quadropole-Bound Electronically Excited States of Closed-Shell Anions Formed by Deprotonation of Cyano- and Ethynyl-Disubstituted Polycyclic Aromatic Hydrocarbons

Dicyano-functionalized benzene and naphthalene anion derivatives exhibit a relatively rich population of electronically excited states in stark contrast to many assumptions regarding the photophysics of anions in general. The present work has quantum chemically analyzed the potential electronically excited states of closed-shell anions created by replacing hydrogen atoms with valence-bound lone pairs in benzene and naphthalene difunctionalized with combinations of -CN and -C2H. Dicyanobenzene anion derivatives can exhibit dipole-bound excited states as long as the cyano groups are not in para position to one another. This also extends to cyanoethynylbenzene anions as well as deprotonated dicyano- and cyanoethynylnaphthalene anion derivatives. Diethynyl functionalization is less consistent. While large dipole moments are created in some cases for deprotonation on the -C2H group itself, the presence of electronically excited states beyond those that are dipole-bound is less consistent. Beyond these general trends, 2-dicyanonaphthalene-34 gives strong indication for exhibiting a quadrupole-bound excited state, and the 1-cyanoethynylnaphthalene-29 and -36 anion derivatives are shown to possess as many as two valence-bound excited states and one dipole-bound excited state. These photophysical properties may have an influence on regions where polycyclic aromatic hydrocarbons are known to exist such as in various astrochemical environments or even in combustion flames.

Different types of interactions between fullerene C60 and C70 anions and metal tetraphenylporphyrins in the (PMDAE+)(MIITPP)(Fullerene−)⋅Solvent complexes (M = Co, Mn, Zn) containing coordinating N, N, N, N‘, N‘-pentamethyldiaminoethane cations

Series of anionic salts of fullerenes C60 and C70 with different metal tetraphenylporphyrins, MIITPP, where M = Co, Mn and Zn, and N, N, N, N‘, N‘-pentamethyldiaminoethane cations (PMDAE+) has been obtained in a crystalline form. Composition of the complexes is (PMDAE+)⋅(MIITPP)(C60−)⋅XC6H4Cl2 (M = Co, X = 1.25 (1), M = Mn, X = 0.75 (2) and M = Zn, X = 0.75 (3)) and {(PMDAE+)⋅ZnIITPP}2⋅(C70−)2⋅4C6H4Cl2 (4). Both fullerene anion and nitrogen-containing PMDAE+ cation can coordinate to metal porphyrin competing with each other. Weak Co-C(C60−) coordination bond of 2.426(7) Å length (120 K) is formed in 1 whereas PMDAE+ cation only weakly coordinates to CoIITPP. Dissociation of Co-C(C60−) bond observed at 90–310 K is accompanied by a transition of 1 from singlet to triplet state with an energy gap of 574 ± 3 K. According to the calculations negative charge on C60− is only −0.548 due to electron transfer to the macrocyclic ligand through the cobalt atom. Charge transfer bands are observed in {CoIITPP(C60)}− at 700 and 1240 nm. On the contrary, PMDAE+ cations coordinate to MnIITPP and ZnIITPP in 2 and 3, respectively, with short M−N(PMDAE+) bonds of 2.27–2.33 Å length. In these cases fullerenes are preserved in the non-coordinated radical anion state. Fullerenes are arranged in closely packed π-stacking {C60•−}2 dimers with short interfullerene center-to-center distances of 9.92–9.95 Å. Nevertheless, the C60•− radical anions do not form intercage CC bonds down to 1.9 K. Strong antiferromagnetic coupling of spins is observed in the {C60•−}2 dimers of 3 with exchange interaction of J/kB = -21 K. Both {(PMDAE+)⋅MnIITPP} and C60•− species are paramagnetic in 2 having S = 5/2 and S = 1/2 spin states, respectively. These spins are coupled antiferromagnetically with Weiss temperature of −16 K. It is obvious that magnetic coupling occurs not only in the {C60•−}2 dimers but MnIITPP is also involved in this coupling. The C70•− radical anions are dimerized in 4 forming diamagnetic singly-bonded (C70−)2 dimers which manifest intense NIR absorption. As a result, complex 4 is EPR silent.

A systematic investigation to unravel the primary determinant of the operational stability of blue fluorescent organic light-emitting diodes

The primary factor that affects the lifetime of blue FOLEDs is the bond dissociation energy (BDE) in anionic state. The BDE of host molecules has a greater impact on the lifetime than that of electron blocking layer molecules.

Molecular structure, homo-lumo analysis and vibrational spectroscopy of the cancer healing pro-drug temozolomide based on dft calculations

<abstract> <p>The molecular structure and spectroscopic analysis of the Temozolomide molecule have been performed using the density functional theory in neutral and anion states as well as with the addition of DMSO solvent. The 6-311G(d) basis set was employed to optimize the molecular structure of the TMZ molecule using the DFT/B3LYP method. The HOMO-LUMO energies and MEP map were computed to determine the energy gap and probable sites of electrophilic and nucleophilic reactivity in the 6-311G+(d) basis set. The vibrational frequencies were calculated using a computational method and the major fundamental modes of vibration were assigned to their respective frequencies. The potential of the computational method to explain the vibrational modes was determined by comparing simulated spectra with experimental spectra. On isotope labeling of carbon, the frequency was shifted significantly.</p> </abstract>

Структура межфазной границы полианилин-углеродная нанотрубка

The analysis of the structure and chemical state of the polyaniline/multi-walled carbon nanotube interface layer was carried out using the both methods of Near Edge X-Ray Absorption Fine Structure and X-Ray Photoelectron Spectroscopy. An analysis of the photoelectron spectra showed an increase in the content of covalently bound chlorine, which may be due to the functionalization of nanotubes during the polymer synthesis. The spectrum shows two states of the chloride anion, which are assigned to the polaron (Cl*) and bipolaron (Cl–) forms of PANI. The content of Cl* increases in the interface layer, which indicates an increase in its electrical conductivity.

Structure of the polyaniline-carbon nanotube interface

The analysis of the structure and chemical state of the polyaniline/multi-walled carbon nanotube interface layer was carried out using the both methods of Near Edge X-Ray Absorption Fine Structure and X-Ray Photoelectron Spectroscopy. An analysis of the photoelectron spectra showed an increase in the content of covalently bound chlorine, which may be due to the functionalization of nanotubes during the polymer synthesis. The spectrum shows two states of the chloride anion, which are assigned to the polaron (Cl*) and bipolaron (Cl-) forms of polyaniline. The content of Cl* increases in the interface layer, which indicates an increase in its electrical conductivity. Keywords: polyaniline, multi-walled carbon nanotubes, composites, X-ray spectroscopy.

Solvent coordination to palladium can invert the selectivity of oxidative addition.

Reaction solvent was previously shown to influence the selectivity of Pd/PtBu3-catalyzed Suzuki–Miyaura cross-couplings of chloroaryl triflates. The role of solvents has been hypothesized to relate to their polarity, whereby polar solvents stabilize anionic transition states involving [Pd(PtBu3)(X)]− (X = anionic ligand) and nonpolar solvents do not. However, here we report detailed studies that reveal a more complicated mechanistic picture. In particular, these results suggest that the selectivity change observed in certain solvents is primarily due to solvent coordination to palladium. Polar coordinating and polar noncoordinating solvents lead to dramatically different selectivity. In coordinating solvents, preferential reaction at triflate is likely catalyzed by Pd(PtBu3)(solv), whereas noncoordinating solvents lead to reaction at chloride through monoligated Pd(PtBu3). The role of solvent coordination is supported by stoichiometric oxidative addition experiments, density functional theory (DFT) calculations, and catalytic cross-coupling studies. Additional results suggest that anionic [Pd(PtBu3)(X)]− is also relevant to triflate selectivity in certain scenarios, particularly when halide anions are available in high concentrations.

Anionic states of C6Cl6 probed in electron transfer experiments.

This is the first comprehensive investigation on the anionic species formed during collisions of fast neutral potassium (K) atoms with neutral hexachlorobenzene (C6Cl6) molecules in the laboratory frame range from 10 up to 100 eV. In such ion-pair formation experiments we also report a novel K+ energy loss spectrum obtained in the forward scattering giving evidence of the most accessible electronic states. The vertical electron affinity of (-3.76 ± 0.20) eV has been obtained and assigned to a purely repulsive transition from the C6Cl6 ground state to a state of the temporary negative ion yielding Cl- formation. These experimental findings are also supported by state-of-the art theoretical calculations on the electronic structure of C6Cl6 in the presence of a potassium atom and are used for analysing the lowest unoccupied molecular orbitals participating in the collision process. From the time-of-flight mass spectra recorded in the wide collision energy range, more than 80% of the total anion yield is due to the undissociated parent anion C6Cl6-, C6Cl5- and Cl- formation. Other fragment anions such as C6Cl4-, C3Cl2-, C2Cl- and Cl2- that undergo complex internal reactions with the temporary negative ion formed after electron transfer account for less than 20% of the total yield. The joint experimental and theoretical methodologies employed in these electron transfer studies provide the most comprehensive and unique assignments of the hexachlorobenzene anionic species and the role of C6Cl6 electronic states in collision induced dissociation to date.

Complexes of transition metal carbonyl clusters with tin(II) phthalocyanine in neutral and radical anion states: methods of synthesis, structures and properties.

Coordination of tin(II) phthalocyanine to transition metal carbonyl clusters in neutral {SnII(Pc2-)}0 or radical anion {SnII(Pc˙3-)}- states is reported. Direct interaction of Co4(CO)12 with {SnII(Pc2-)}0 yields a crystalline complex {Co4(CO)11·SnII(Pc2-)} (1). There is no charge transfer from the cluster to phthalocyanine in 1, which preserves the diamagnetic Pc2- macrocycle. The Ru3(CO)12 cluster forms complexes with one or two equivalents of {SnII(Pc˙3-)}- to yield crystalline {Cryptand[2.2.2](Na+)}{Ru3(CO)11·SnII(Pc˙3-)}- (2) or {Cryptand[2.2.2](M+)}2{Ru3(CO)10·[SnII(Pc˙3-)]2}2-·4C6H4Cl2 (3) (M+ is K or Cs). Paramagnetic {SnII(Pc˙3-)}- species in 2 are packed in π-stacking [{SnII(Pc˙3-)}-]2 dimers, providing strong antiferromagnetic coupling of spins with exchange interaction J/kB = -19 K. Reduction of Ru3(CO)12, Os3(CO)12 and Ir4(CO)12 clusters by decamethylchromocene (Cp*2Cr) and subsequent oxidation of the reduced species by {SnIVCl2(Pc2-)}0 yield a series of complexes with high-spin Cp*2Cr+ counter cations (S = 3/2): (Cp*2Cr+){Ru3(CO)11·SnII(Pc˙3-)}-·C6H4Cl2 (4), (Cp*2Cr+){Os3(CO)10Cl·SnII(Pc˙3-)}-·C6H4Cl2 (5) and (Cp*2Cr+){Ir4(CO)11·SnII(Pc˙3-)}2- (6). It is seen that reduced clusters are oxidized by SnIV, which is transferred to SnII, whereas the Pc2- macrocycle is reduced to Pc˙3-. In the case of Os3(CO)12, oxidation of the metal atom in the cluster is observed to be accompanied by the formation of Os3(CO)10Cl with one OsI center. Rather weak magnetic coupling is observed between paramagnetic Cp*2Cr+ and {SnII(Pc˙3-)}- species in 4, but this exchange interaction is enhanced in 5 owing to Os3(CO)10Cl clusters with paramagnetic OsI (S = 1/2) also being involved in antiferromagnetic coupling of spins. The formation of {SnII(Pc˙3-)}- with radical trianion Pc˙3- macrocycles in 2-5 is supported by the appearance of new absorption bands in the NIR spectra and essential Nmeso-C bond alternation in Pc (for 3-5). On the whole, this work shows that both diamagnetic {SnII(Pc2-)}0 and paramagnetic {SnII(Pc˙3-)}- ligands substitute carbonyl ligands in the transition metal carbonyl clusters, forming well-soluble paramagnetic solids absorbing light in the visible and NIR ranges.

Computational Study on Vibrational Properties of Thyroxine Molecule in Different Charge States

The vibrational frequencies of thyroxine (T4) molecule are calculated through computational method and major modes of vibration are assigned to corresponding frequencies in this research work. First we took neutral isolated T4 molecule for our study, and then we extend our work to anion state. The shift produced in the frequency and IR intensities for different vibrational modes has been calculated for change in state from neutral to anion. In addition, the difference spectra for these two charge states has also been studied for the T4 molecule by adding the dimethyl sulfoxide (DMSO) solvent. Furthermore, the same calculations are performed for the isolated neutral T4 molecule with C13 labelling. All these calculations are carried out by density functional calculations with the B3LYP hybrid functional applying the SDD effective core potential basis set. The calculated geometrical parameters are in good agreement with the experimental results. Additionally, the calculated frequencies lies within the characteristic region belonging to the respective mode of vibrations.

Electro-optical, electronic and conformational transitions of interstellar alkyl molecules at different temperatures: An ab-initio study

In this paper, electronic structures of iso-propyl cyanide (i-C3H7CN), gauche-normal-propyl cyanide (g-n-C3H7CN) and anti-normal-propyl cyanide (a-n-C3H7CN) have been optimized using DFT/B3LYP/aug-cc-pVDZ and DFT/CAM-B3LYP/aug-cc-pVDZ methods in neutral and anionic states. Electro-optical properties, HOMO, LUMO and MEP surfaces have been computed in order to check the optical behaviour and chemical reactivity of these interstellar molecules. The a-n-C3H7CN molecule exhibits better electro-optical behaviour than g-n-C3H7CN and iso-C3H7CN molecules. Global reactivity descriptors, adiabatic and vertical electron affinities of these straight and branched alkyl molecules have been investigated. These molecules have negative electron affinities, which means that they emit energy in anionic form. The distribution of chemical bonding and electron lone pairs inside molecules has been discussed using ELF map. Infrared and absorption spectra of these interstellar molecules have been studied in the light of experimental data. Further, formations of g-n-C3H7CN from i-C3H7CN, a-n-C3H7CN from i-C3H7CN and a-n-C3H7CN from g-n-C3H7CN have been examined using transition state at 10 ​K, 298.15 ​K and 500 ​K temperatures. Mechanism of formation of g-n-C3H7CN and a-n-C3H7CN from i-C3H7CN at 10 ​K, 298.15 ​K and 500 ​K temperatures along with their physico-chemical properties have been elucidated.

Spin-dependent vibronic response of a carbon radical ion in two-dimensional WS2

Atomic spin centers in 2D materials are a highly anticipated building block for quantum technologies. Here, we demonstrate the creation of an effective spin-1/2 system via the atomically controlled generation of magnetic carbon radical ions (CRIs) in synthetic two-dimensional transition metal dichalcogenides. Hydrogenated carbon impurities located at chalcogen sites introduced by chemical doping are activated with atomic precision by hydrogen depassivation using a scanning probe tip. In its anionic state, the carbon impurity is computed to have a magnetic moment of 1 μB resulting from an unpaired electron populating a spin-polarized in-gap orbital. We show that the CRI defect states couple to a small number of local vibrational modes. The vibronic coupling strength critically depends on the spin state and differs for monolayer and bilayer WS2. The carbon radical ion is a surface-bound atomic defect that can be selectively introduced, features a well-understood vibronic spectrum, and is charge state controlled.

Observation of the ponderomotive effect in non-valence bound states of polyatomic molecular anions

The ponderomotive force on molecular systems has rarely been observed hitherto, despite potentially being extremely useful for the manipulation of the molecular properties. Here, the ponderomotive effect in the non-valence bound states has been experimentally demonstrated, for the first time to the best of our knowledge, giving great promise for the manipulation of polyatomic molecules by the dynamic Stark effect. Entire quantum levels of the dipole-bound state (DBS) and quadrupole-bound state (QBS) of the phenoxide (or 4-bromophenoxide) and 4-cyanophenoxide anions, respectively, show clear-cut ponderomotive blue-shifts in the presence of the spatiotemporally overlapped non-resonant picosecond control laser pulse. The quasi-free electron in the QBS is found to be more vulnerable to the external oscillating electromagnetic field compared to that in the DBS, suggesting that the non-valence orbital of the former is more diffusive and thus more polarizable compared to that of the latter.

Operational lifetime improvement of solution-processed OLEDs: Effect of exciton formation region and degradation analysis by impedance spectroscopy

It is known that the lifetime of the organic light-emitting diode device manufactured by the solution process is deteriorated due to the problem of mixing the interface between the hole transport layer and the emitting layer. We found that moving the recombination area away from the interface mixing zone as above doubled the efficiency (22.8 cd/A → 51.5 cd/A, 7.6% EQE → 14.6% EQE) and tripled the lifetime (14 h → 42 h). The reason was mainly attributed to the suppression of degradation due to exciton-polaron quenching at the mixing interface. Especially, the degradation of solution-processed devices has not been widely discussed. Therefore, in this study, we investigated thoroughly the deterioration of those devices by impedance spectroscopy and molecular simulation. The trap sites were revealed to present at the mixing zone when a large amount of charges accumulating there. These traps potentially resulted from the fragment of molecules undergoing the bond dissociation due to quenching of exciton and negative charge. Furthermore, by fitting Cole-Cole plots, we observed that the most stress region after half-lifetime test was the mixing zone. To confirm which molecules have a high possibility to dissociate, we calculated the bond dissociation energy of the possible dissociated bonds. The dissociation of host molecules from the anionic excited state due to quenching of exciton and negative polaron played the main role in device degradation. Meanwhile, the dissociation of hole transport molecules in the anionic charged states could also affect device lifetime by slow degradation.

Quantum computational, spectroscopic and molecular docking studies of potent tuberculosis drug 2,6-dihydroxypyridine-4-carboxylic acid and 2‑hydroxy -6-methylpyridine-4-carboxylic acid

This study reports the molecular structure and spectroscopic (FT-IR, FT-Raman, UV–Vis, 1H and 13C NMR) investigations of 2,6-dihydroxypyridine-4-carboxylic acid (HPC) (citrazinic acid) and 2‑hydroxy -6-methylpyridine-4-carboxylic acid (HMPC) molecules. The quantum computational calculations were performed by density functional theory (DFT) method using the B3LYP/ 6–311++G (d,p) basis set. The vibrational wavenumbers and NMR chemical shifts were matched well with the experimental data. The title molecules exhibited two kinds of dimers such as J and H- type dimers. The Mulliken atomic charge distribution for neutral, anionic, and cationic states was performed to predict Fukui function and global softness of the molecules. From the molecular electrostatic potential (MEP) map the reactive sites were identified and the reactivity of the title compounds was examined through the HOMO-LUMO energy gap. Natural Bonding Orbital (NBO) analysis revealed that the presence of stabilization interactions within the title molecules. In addition, the molecular docking studies carried out for title molecules to determine protein ligand interaction to confirm the inhibition activity against Mycobacterium tuberculosis. Additionally, the non-linear optical property was also calculated for title molecules.

Putting Anion-π Interactions at Work for Catalysis.

Since its discovery two decades ago, anion-π interaction has been increasingly recognized as an important driving force. Extensive theoretical and experimental efforts on the ground-state anion-π binding and recognition have laid the bases for exploring its relevance in catalysis. Accordingly, the concept of "anion-π catalysis" that employing an electron-deficient π surface (π-acidic surface) for anionic reaction intermediate and transition state stabilization has emerged. This article shortly reviews the emergence and development of this concept, aiming to provide an emphasis on the general concept and key progress in this exciting area. To highlight the essential contribution of anion-π interactions, the contents are organized according to their role engaged in catalytic process, for example from both ground-state and transition-state stabilization to solely transition-state stabilization, mainly by a single π-face, and to cooperative π-face activation. A concluding remark and outlook on future development of this field is also given.