Penning spectroscopy studies molecules

Abstract

Study of outermost surface lavers of organic solids by penning ionization electron spectroscopy

A general procedure for evaluating the number of cluster valence molecular orbitals in molecules with condensed polyhedral geometries has been derived from molecular orbital calculations and shown to be widely applicable.

Opto‐electronic properties and device performance of organic semiconductors are mainly determined by energy levels of their frontier molecular orbitals, e.g. lowest unoccupied molecular orbital (ELUMO) and highest occupied molecular orbital (EHOMO) in the ground state, first singlet state (ES1) and first triplet state (ET1) in the excited state. These energy levels are always intricately intertwined. Herein, we report a series of monodisperse oligomers based on double B←N bridged bipyridine (BNBP) units. With the increasing number of repeating units, the oligomers exhibit gradually downshifted ELUMO and nearly unchanged EHOMO due to the different distribution of the frontier molecular orbitals of the oligomers. Moreover, the oligomers exhibit gradually decreasing ES1 and nearly unchanged ET1 because of the different contributions of the charge transfer component in the excited state. This work provides new insight into energy level tuning of organic semiconductors, which is important for high‐performance organic opto‐electronic devices.

The authors have proposed the formation of dumbbell-shape graphene nanoribbon (DS-GNR) by changing the width of the mid-part of a GNR in order to enhance the stability and reliability of the GNR-based electronic devices. In this study, the electronic band structure of the DS-GNR was analyzed by using the first principle calculation method. Throughout the calculation, the electronic band structures, densities of states, and orbital distributions were examined to describe the electronic properties of DS-GNRs. The band gap of DS-GNRs is different to that of single GNRs because the orbital distributions of the lowest unoccupied molecular orbitals (LUMO) and the highest occupied molecular orbitals (HOMO) in DS-GNRs changed from those in single GNRs. Generally, single GNRs exhibit both the semiconducting and the metallic properties depending on the ribbon width. The magnitude of the band gap of DS-GNRs depends on the difference in the width of narrow part and wide parts, and the variation of the band gap of DS-GNRs was smaller than that of single GNRs. In addition, when a dumbbell-shape GNR undergoes a uniaxial tensile strain, its band gap showed high strain sensitivity as was expected. Therefore, the GNR material with a dumbbell-shape structure has great potential for use in highly sensitive strain sensors.

A new reaction scheme is proposed to account for roaming and chaotic behaviors in collisional and photo-initiated molecular-beam reactions, where nonadiabatic dynamics plays a key role and the collapse of superposition of wave functions is considered to be important in the beginning of the present scheme. Since the feature of molecular orbitals of reagents is crucial in reaction, we showed how to map out the spatial distribution of the relevant HOMO molecular orbitals of CH3Cl in the impact of fast electrons. We identified by experiment that the multiple overlap of nearby molecular orbitals affects even the vibrational motion of adjacent molecule DCl of the transient [ClDCl] chemical species. We also showed dynamical steric effects in the HBr + OH four-atom reaction as a manifestation of the nonadiabatic dynamics in complex systems. The roaming mechanism in the photo-initiated reaction of methyl formate is clarified in detail by experiment as well as the QCT trajectory calculation, where the conical intersection region plays an essential role. We suggest that two types of roaming trajectories coexist, i.e., deterministic and chaotic roaming trajectories based on classical trajectory calculations. To clarify the nonadiabatic dynamics in the roaming mechanism for non-collinear three-dimensional (3D) collisions, a new model of the 3D Polanyi rule is proposed as the extension of the well-established 2D Polanyi rule. In the 3D Polanyi rule, it is expected that the curvature and torsion of Frenet–Serret formulas in three-dimensional space would provide us key concepts in understanding reaction dynamics.

Dissociative electron attachment to an octafluorocyclopentene (c-C5F8) molecule has been investigated by means of ab initio molecular orbital calculations. Because of the antibonding character of the virtual valence orbitals, the temporary anions dissociate, producing neutral and negative radical fragments in reactive plasma. In order to identify the valence of virtual orbitals associated with the dissociative electron attachment in the calculation with the diffuse basis set, we examined the spatial distribution and antibonding characteristics of the virtual molecular orbitals. This theoretical approach reproduced experimental resonance energies of the dissociative electron attachment, which display rich resonance energy spectra as observed by electron attachment mass spectrometry.

Realizing External Quantum Efficiency over 25% with Low Efficiency Roll-Off in Polymer-Based Light-Emitting Diodes Synergistically Utilizing Intramolecular Sensitization and Bipolar Thermally Activated Delayed Fluorescence Monomer

The molecular orbitals and first ionization potentials calculation of iodine compounds

The electronic structure of a model surface consisting of a Ni diatom and an ethylene molecule has been calculated using the self-consistent-field, $X\ensuremath{\alpha}$, scattered-wave method. Comparison of calculated $\ensuremath{\pi}$-orbital bonding shifts with recent photoemission spectra for chemisorption of ethylene on nickel favors a $\ensuremath{\pi}$-bonded complex over a di-$\ensuremath{\sigma}$-adsorbed complex. Charge distributions of various molecular orbitals indicate that the C-C double bond is weakened more for the latter molecular arrangement, suggesting such a complex as a likely intermediate in heterogeneous reactions.

Assignment of photoelectro bands for naphthalene and anthracene by penning ionization electron spectroscopy

Today, Alzheimer’s disease (AD) is one of the most important neurodegenerative disorders that affected millions of people worldwide. Hundreds of academic investigations highlighted the potential roles of natural metabolites in the cornerstone of AD prevention. Nevertheless, alkaloids are only metabolites that successfully showed promising clinical therapeutic effects on the prevention of AD. In this regard, other plant metabolites such as flavonoids are also considered as promising substances in the improvement of AD complications. The lack of data on molecular mode of action of flavonoids inside brain tissues, and their potential to transport across the blood-brain barrier, a physical hindrance between bloodstream and brain tissues, limited the large-scale application of these compounds for AD therapy programs. Herein, a coupled docking and quantum study was applied to determine the binding mode of flavonoids and three protein kinases involved in the pathogenesis of AD. The results suggested that all docked metabolites showed considerable binding affinity to interact with target receptors, but some compounds possessed higher binding energy values. Because docking simulation cannot entirely reveal the potential roles of ligand substructures in the interaction with target residues, quantum chemical analyses (QCAs) were performed to cover this drawback. Accordingly, QCAs determined that distribution of molecular orbitals have a pivotal function in the determination of the type of reaction between ligands and receptors; therefore, using such quantum chemical descriptors may correct the results of virtual docking outcomes to highlight promising backbones for further developments. Communicated by Ramaswamy H. Sarma

Through the use of scanning tunnelling microscopy (STM), it is possible to directly observe the molecular orbitals associated with a particular molecule. For the charged ions of the C60 fullerene, the interpretation of these experimental images has an additional complication due to the inherent presence of the Jahn-Teller (JT) effect. In this work, the influence of the JT effect on STM images is examined. We also include interactions between the molecule and both the surface substrate on which it rests, and, when present within a monolayer, the nearest neighbours. Simple symmetry arguments are used to explain the effects of these external interactions on the energy of the different JT wells relating to molecular distortions of D3d, D5d, and D2h symmetry. We first investigate the C−60 monoanion, and then, through the construction of multi-electron states, move on to consider anions with higher charges. It is found that for high symmetry orientations of the molecule on the surface, the wells that are degenerate in the absence of external interactions split into equal energy subgroups, with the grouping dependent on the orientation of the molecule. Hückel molecular orbital theory is then used to investigate the effect this has on STM images. We show that when dynamic JT effects are considered, the images are always formed from some linear combination of the squares of the individual single electron molecular orbitals that make up the lowest unoccupied molecular orbital of the neutral molecule.

Accuracy of the fragment molecular orbital (FMO) calculations for DNA: Total energy, molecular orbital, and inter-fragment interaction energy

Inspired by the dominant role of 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene) malononitrile (INCN) terminal in regulating molecular packing, an innovative strategy to construct “third terminals” of non‐fullerene acceptors (NFAs) is proposed by introducing INIC‐mimicking motifs to molecular backbone center. Through delicate electrostatic and geometric regulation of INCN analogues (NQ, DCNQ, and TCNC), newly designed NFAs (CH56, CH57, and CH58) render not only an inverted distribution of molecular frontier orbitals, but also the substantial HOMO–LUMO overlap for CH56 while pronounced spatial separation for others. Especially, the puckered TCNC with the most LUMOs distribution yet minimal involvement in molecular packings drives CH58 to adopt a pseudo‐three‐dimensional (3D) packing network and inferior electron migration in sharp contrast to CH56. Moreover, the twisty CH57 and CH58 also exhibit unexpectedly quenched fluorescence due to the severe skeletal vibrations DCNQ and TCNC, further resulting in the large energy losses and poor photovoltaic performance. Finally, CH56‐based OSCs yield a surprising open‐circuit‐voltage of 1.007 V for binary devices and an excellent 20.16% efficiency for ternary devices. Our trials on “third terminal” has enabled the extensive exploration of novel architectures of NFAs beyond conventional structural paradigms.