Journal of Theoretical and Computational Chemistry

Ab initio and density functional theory calculations were used to determine structure and inversion barrier at phosphorous (III) for open and cyclic phosphorus-containing compounds. Structures of the investigated systems were compared with the available experimental data. Effects of ring size on the P-inversion barriers in these molecules have been discussed. The largest/smallest inversion barrier was reported for phosphocyclopropene/trivinylphosphine (85.1/21.0 kcal/mol). Inversion rate and half-life time were computed.

Benzenoid chains are natural graph representations of chain hydrocarbons. For a given benzenoid chain $H$, we find an expression of its second-order general connectivity index, denoted by ${}^2{\chi }_{\alpha }(H)$, in terms of inlet features of $H$. It is also shown that the second-order general connectivity index ${}^2{\chi }_{\alpha }(H)$ correlates well with the $\pi$-electronic energy of $H$ for $\alpha \in [-0.5,0.5]$, especially for $\alpha =0.237617$.

The density functional theory (B3PW91/6-311$++$G(2d,2p)) was used to obtain optimized geometry, energy and electronic properties of Mg${}_n\dots$EtBr adsorption complexes, Et$\dots$Mg${}_n\dots$Br intermediates and transition states for ethyl bromide reaction with the magnesium atom and Mg_n ($n=2$–20) clusters modeling the distorted surface of the metallic magnesium. We suggest a consecutive multi-stage scheme of EtBr$+$Mg_n process in vacuum that includes adsorption of reagents on external cluster atoms, chemical interaction with Grignard reagent formation and desorption of products to the volume. Two fundamentally different reaction channels were investigated — the radical and molecular ones. Influence of Mg_n cluster size on the preference of each of channels was established. It is shown that the reaction route is primarily determined with the position of the reactive group of atoms participating in formation of the transition state or radical intermediates and the activation energy of EtMgBr formation correlates with the energy of atom detachment from a cluster. For both pathways, reaction activation energies and thermodynamic parameters of the elementary steps were calculated.

Molecular dynamics simulations of wild type and two mutant (T248F and L251T) human $\alpha$7 nicotinic acetylcholine receptors (nAChR) have been performed. The channel transmembrane domains were modeled from the closed channel structure from torpedo ray (PDB ID 2BG9) and embedded in DPPC lipid bilayers, surrounded by physiological saline solution. An external electric field was used to obtain stable open channel structures. The adaptive biasing force (ABF) method was used to obtain potential of mean force (PMF) profiles for Na${}^{+}$ ion translocation through the wild type and mutant receptors. Based on the geometry and PMF profiles, the channel gate was found to be at one of the two hydrophobic conserved regions (V249-L251) near the lower end of the channel. The L251T mutation reduced the energetic barrier by 1.9kcal/mol, consistent with a slight increase in the channel radius in the bottleneck region. On the other hand, the T248F mutation caused a significant decrease in the channel radius (0.4 Å) and a substantial increase of 3.9kcal/mol in the energetic barrier. Ion permeation in all three structures was compared and found to be consistent with barrier height values. Using an external field in an incrementally increasing manner was found to be an effective way to obtain stable open, conducting channel structures.

A probabilistic approach to characterizing transit times for quantum particles is generalized to a system of more than two spatial regions and applied to the transport of charge in donor-bridge-acceptor systems. The approach is based on applying conditional probability analysis to a discrete representation of the time-dependent probability density as generated by numerical solution of the time-dependent Schrödinger equation for an initially localized electron. To carry out this analysis, it is first necessary to cast the conditional probability analysis approach in matrix form. The results afford a quantification of the electron transit time and may provide a tool to gain insight into the mechanism of charge transport.

We present a quasiclassical trajectory study of the photodissociation of CD₃CHO based on a global ab initio-based potential energy surface. Calculations are performed at the total energy corresponding to the photolysis wavelength of 280nm. In addition to the major radical and molecular products, CD${}_3+\mathrm{\text{HCO}}$ and CD₃H $+$ CO, respectively, this paper focuses on the unusual radical channel CD₂H $+$ DCO, which requires a D/H exchange process before the conventional C–C bond cleavage. Five D/H exchange mechanisms are reported, which are related to the isomerizations from acetaldehyde to vinyl alcohol and back, to oxirane and back, and to the intermediate (CD–CHD–OD) and back. These D/H exchange mechanisms are in good agreement with the experimental findings [Heazlewood BR, Maccarone AT, Andrews DU, Osborn DL, Harding LB, Klippenstein SJ, Jordan MJT, Kable SH, Nat Chem 3:443, 2011].

We theoretically investigated the combination of D-A and D-spacer (phenyl ring)-A with an electron donating alkyl (t-butyl) group. The strategy of twisting the geometry of the molecule with the alkyl substituents exclusion of strong electron-withdrawing or -donating groups leads to gain efficient deep blue-to-blue thermally activated delayed fluorescence (TADF) emitter through maintaining the band gap while the reduction of singlet-triplet energy gap ($E_{\mathrm{\text{ST}}})$. The t-butyl group strongly twisted the conformation of molecules by the steric hindrance, which resulted in weak highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) overlap ($I_{H∕L})$ and efficient spatial separation of HOMO and LUMO ($r_{H∕L})$ in the $S_0$ state. In contrast, designed molecules $S_1$ state own large HOMO and LUMO overlap of excited singlet state ($I_S)$ and inefficient spatial separation of HOMO and LUMO. The computed results indicated that introducing alkyl group into the phenyl ring of the acceptor of the designed molecules cannot affect the $\mathrm{\Delta }{E}_{\mathrm{\text{ST}}}$. The $\mathrm{\Delta }{E}_{\mathrm{\text{ST}}}$ is mainly related to the $I_{H∕L}$, which can be adjusted by tuning the orbital $I_{H∕L}$. The large modular orbital overlap at $S_1$ and $T_1$ excited states resulted in large $\mathrm{\Delta }{E}_{\mathrm{\text{ST}}}$, which occurs in the range of 0.38–0.59eV whose dominant contribution switches from charge transfer to local excitation. Our studied results reiterate (10.1038/srep10923) that modular orbital overlap of $I_S$, HOMO and LUMO overlap of excited triplet state $I_T$, spatial separation of HOMO and LUMO in the excited singlet state ($r_S)$, and spatial separation of HOMO and LUMO in the excited triplet state ($r_T)$ are the essential factors to determine $\mathrm{\Delta }{E}_{\mathrm{\text{ST}}}$ when inconsistencies between $\mathrm{\Delta }{E}_{\mathrm{\text{ST}}}$ and $I_{H∕L}$ exist. Increasing the dihedral angle between $D$ and $A$ from molecules 1–4 (9–12) decreases the transition dipole moment, which lowers the oscillator strength. When changing the connection position between $D$ and $A$, molecules 5–8, the oscillator strength reduced to half with respect to molecules 1–4 and 9–12. The present work provides a theoretical understanding of the impact of alkyl substituents on the overlap of HOMO–LUMO resulting to tuning the $\mathrm{\Delta }{E}_{\mathrm{\text{ST}}}$, as well as its influence on the oscillator strength, which may be a reliable idea to design efficient TADF emitters.