Double-boron heterocyclic carbenes: a computational study of Diels-Alder reactions.

An aromatic boron-containing organic compound, CBH, with an unusual CC bond was experimentally synthesized in 2017. Here we investigate the structure and bonding nature of CBH and its derivatives CBR using DFT and VB theory. Although the CC bond in CBR consists of a π bond and a charge-shift (CS) bond, CBF has the lowest LUMO energy and its LUMO is similar to that of ethylene, suggesting that CBF can be an ideal dienophile for the Diels-Alder reaction.

Enhancing Reverse Intersystem Crossing in Triptycene-TADF Emitters: Theoretical Insights into Reorganization Energy and Heavy Atom Effects.

Thermally activated delayed fluorescence (TADF) emitters based on the triptycene skeleton demonstrate exceptional performance, superior stability, and low efficiency roll-off. Understanding the interplay between the luminescent properties of triptycene-TADF molecules and their assembly environments, along with their excited-state characteristics, necessitates a comprehensive theoretical exploration. Herein, we predict the photophysical properties of triptycene-TADF molecules in a thin film environment using the quantum mechanics/molecular mechanics method and quantify their substantial dependency on the heavy atom effects and reorganization energies using the Marcus-Levich theory.

Designing thermally activated delayed fluorescence emitters with through-space charge transfer: a theoretical study.

Recently, thermally activated delayed fluorescence (TADF) molecules with through-space charge transfer (TSCT) features have been widely applied in developing organic light-emitting diodes with high luminescence efficiencies. The performance of TSCT-TADF molecules depends highly on their molecular structures. Therefore, theoretical investigation plays a significant role in designing novel highly efficient TSCT-TADF molecules.

Thermally activated delayed fluorescence materials with aggregation-induced emission properties: a QM/MM study.

Organic molecules with thermally activated delayed fluorescence (TADF) and aggregation induced emission (AIE) properties have attracted increasing research interest due to their great potential applications in organic light emitting diodes (OLEDs), especially for those with multicolor mechanochromic luminescence (MCL) features. Theoretical research on the luminescence characteristics of organic TADF emitters based on the aggregation states is highly desired to quantify the relationship between the TADF properties and aggregation states. In this work, we study the 4,4'-(6-(9,9-dimethylacridine-10(9)-yl)quinoline-2,3-dibenzonitrile (DMAC-CNQ) emitter with TADF and AIE properties, and calculate the photophysical properties in gas, solid and amorphous states by using the quantum mechanics and molecular mechanics (QM/MM) method.

Cross Conjugation in Polyenes and Related Hydrocarbons: What Can Be Learned from Valence Bond Theory about Single-Molecule Conductance?

This study examined the nature of the electronic structure of representative cross-conjugated polyenes from a valence bond (VB) perspective. Our VBSCF calculations on a prototypical dendralene model reveal a remarkable inhibition of the delocalization compared to linear polyenes. Especially along the C-C backbone, the delocalization is virtually quenched so that these compounds can essentially be considered as sets of isolated butadiene units.

Clinical significance of expression of proliferating cell nuclear antigen and E-cadherin in gastric carcinoma.

Aim: to investigate the expression of proliferating cell nuclear antigen (PCNA) and E-cadherin in gastric carcinoma and to analyze their clinical significance.

Methods: A total of 146 patients were selected for this study, including 38 patients with intestinal metaplasia, 42 with dysplasia, and 66 with primary gastric cancer. In addition, 40 patients with normal gastric tissues were selected as controls.

Valence Bond Theory Reveals Hidden Delocalized Diradical Character of Polyenes.

The nature of the electronic-structure of polyenes, their delocalization features, and potential diradicaloid characters constitute a fundamental problem in chemistry. To address this problem, we used valence bond self-consistent field (VBSCF) calculations and modeling of polyenes, CH (n = 2-10). The theoretical treatment shows that starting with n = 5, the polyene's wave function is mainly a shifting 1,4-diradicaloid, a character that increases as the chain length increases, while the contribution of the fundamental Lewis structure with alternating double and single bonds (1) decays quite fast and becomes minor relative to the diradicaloid pack.

The mechanism of alopolysaccharide protecting ulceralive colitis.

The aim of this study is to explain the mechanism of alopolysaccharide protecting ulceralive colitis in cells and animal models. We divided this study into two parts: cell and animal research parts. In the cell research, HT-29 cells were divided into normal group, model group, aloe polysacchride group and positive drug group, the cell model was used by tumor necrosis factor- α (TNF-α) combine with LPS, detecting IL-6 concentration of difference groups by Elisa testing, Apoptosis of each group was detected by flow cytometry.

Oxygen-Molecule Adsorption and Dissociation on BCN Graphene: A First-Principles Study.

Boron and nitrogen co-doped (BCN) graphene is an attractive material for use as a metal-free oxygen reduction reaction electrocatalyst and as other catalysts due to its unique structure and electronic properties. Reported here is the structure, determined by using density functional theory, of the active O -dissociation site of BCN graphene containing different types of BN cluster. The results show that the edge termination and shape of substitutional BN clusters are two important factors that determine the catalytic activity of BCN graphene for the dissociation of molecular oxygen.

Nonorthogonal orbital based n-body reduced density matrices and their applications to valence bond theory. III. Second-order perturbation theory using valence bond self-consistent field function as reference.

Using the formulas and techniques developed in Papers I and II of this series, the recently developed second-order perturbation theory based on a valence bond self-consistent field reference function (VBPT2) has been extended by using the internally contracted correction wave function. This ansatz strongly reduces the size of the interaction space compared to the uncontracted wave function and thus improves the capability of the VBPT2 method dramatically. Test calculations show that internally contracted VBPT2 using only a small number of reference valence bond functions, can give results as accuracy as the VBPT2 method and other more sophisticated methods such as full configuration interaction and multireference configuration interaction.

Bonding Conundrums in the C2 Molecule: A Valence Bond Study.

The ab initio VB study for the electronic structure of the C2 molecule in the ground state is presented in this work. VB calculations involving 78 chemically relevant VB structures can predict the bonding energy of C2 quite well. Sequentially, a VBCIS calculation provides spectroscopic parameters that are very close to full CI calculated values in the same basis set.

The inverted bond in [1.1.1]propellane is a charge-shift bond.

Bonded or not bonded? An ab initio valence bond study of [1.1.1]propellane shows that the two bridgehead carbons are linked by a strong and direct sigma bond that is neither classically covalent nor classically ionic, but rather a charge-shift bond, in which the covalent-ionic resonance energy plays the major role.

Covalent Excited States of Polyenes C2nH2n+2 (n = 2-8) and Polyenyl Radicals C2n-1H2n+1 (n = 2-8): An Ab Initio Valence Bond Study.

The ab initio valence bond (VB) methods, VBSCF and VBCI, are applied to the ground states and the covalent excited states of polyenes C2nH2n+2 (n = 2-8) and polyenyl radicals C2n-1H2n+1 (n = 2-8). The excitation energy gap was computed at the ab initio VB level, which is in good agreement with the semiempirical VB method, VBDFT(s), and the experimental values as well as with the molecular orbital theory based methods, CASPT3 and MRCI. The ab initio VB wave functions of systems are also in very good agreement with those of the VBDFT(s) method, even though the former is based on the ab initio VB scheme while the latter is a semiempirical Hückel type method, in which no orbital optimization procedure is performed.