An study on the photoisomerization in 2-styrylpyridine.

We report results of a theoretical study on photoinduced processes in 2-styrylpyridine. The geometries and the relative energies of the possible conformers were investigated using the second-order Møller-Plesset (MP2) and algebraic diagrammatic construction to second-order (ADC(2)) methods and the cc-pVTZ basis set. The complete active space self consistent field (CASSCF) method is used for locating the minimum-energy conical intersection (MECI) geometries between the S and S states.

Contrasting the excited state properties of different conformers of - and -2,2'-bipyridine oligomers in the gas phase.

In this article, we present conformation-dependent photophysical and excited state properties of trans- and cis- BPY oligomers. Oligomers up to tetramers for three conformers, namely, o-, m-, and p-, are constructed and optimized at the B3LYP-D3/def2-SVPD level. The photophysical and excited state properties are interpreted in terms of UV and CD spectra at the RI-ADC(2)/def2-TZVPD level.

Conformational Effect on the Excitonic States of 2-Phenylpyridine Oligomers: Ab Initio Studies and Analysis.

In this work, we report the effect of different conformations of 2-phenylpyridine oligomers (()) on the excited state properties from the results obtained at the RI-ADC(2)/def2-TZVP level. Three different conformers, namely, , , and , are considered for each oligomer. All the oligomers of conformer have linear-type structures, whereas conformers and form helical structures at = 5 and = 3, respectively.

Theoretical Investigation of the / Photoisomerization Pathway in 1-(2-Pyrrolyl)-2-(2-thienyl)ethylene.

Molecular-level understanding of photochemistry in simple vinylene-linked systems such as ethylene and stilbene has been a major area of research. However, the effect of replacing the two benzene rings by five-membered heterocyclic rings, thiophene and pyrrole, is yet to be reported. In the present theoretical study, our aim is to illustrate photoinduced processes in a vinylene-linked thiophene-pyrrole system.

Effect of Fluorine Substitution on Absorption and Emission Properties of Figure-eight-shaped [5]Helicene Dimer: A Computational Study at RI-MP2/RI-ADC(2) Level.

Chirality is a very important characteristic of optically active molecules and polyaromatics with helical structures, and plays a vital role in various applications in material science. In the present work, we show the effects of fluorine substitution at various positions in a figure-8-shaped [5]helicene dimer on the ground and excited state g-factors. Calculations for the ground and excited states are performed at the MP2 and ADC(2) levels of theory, respectively.

Effect of Terminal Fluorination on Chiroptical Properties of Carbo[5-8]helicenes: A Systematic Computational Study at the RI-ADC(2) Level.

In this article, effects of di-, tetra-, and octafluorination on the structural and chiroptical properties of carbo[5-8]helicenes are reported. Three fluorinated derivatives are designed from each parent carbohelicene by substituting either one, two, or four hydrogens at each terminal ring with fluorine atoms. Excited states properties such as UV-vis and CD spectra of all the six fluorinated carbohelicenes are computed at the ADC(2)/def2-TZVP level, and the results are compared against the results of their respective parent carbohelicene.

Improved Estimates of Host-Guest Interaction Energies for Endohedral Fullerenes Containing Rare Gas Atoms, Small Molecules, and Cations.

Endohedral fullerenes have evinced much interest from the fundamental and applications points of view. However, given the nature of the weak interaction between the guest species and the host cage in these confined systems, the interaction energy values obtained using various theoretical methods, and different basis sets vary over a wide range. For example, the reported interaction energy for the HF@C system ranges from -2.

Effects of Heterocyclic Ring Fusion and Chain Elongation on Chiroptical Properties of Polyaza[9]helicene: A Computational Study.

In the present work, the effect of lateral and helical extensions on the physical and chiroptical properties of azahelicenes is reported. Starting with the experimentally reported polyaza[9]helicene (), three derivatives, two with laterally fused electron-withdrawing rings and the third with larger helical length, are designed. For the excited-state properties such as UV-vis and CD spectra, performances of different DFT functionals are evaluated by comparing the energies and characters of the excited states against the ADC(2) results.

Assessing Effects of Different π bridges on Properties of Random Benzodithiophene-thienothiophene Donor and Non-fullerene Acceptor Based Active Layer.

This report presents the effect of insertion of four different π bridges, furan, thienothiophene, thiophene, and thiazole, into a random benzodithiophene (BDT)-fluorinated-thienothiophene (TT-F) based donor. Starting from a structure of synthesized donor (D)-acceptor (A) random copolymer with 3:1 ratio, we have designed four D-π-A systems with four different π bridges. Structural, optoelectronic, and charge transport/transfer properties of these donors and donor/NDI (NDI = poly[,'-bis(2-hexyldecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]--5,5'-(2,2'-bithiophene)) blends are investigated using DFT and TD-DFT methodologies.

Atom-Diatom Reactive Scattering Collisions in Protonated Rare Gas Systems.

The study of the dynamics of atom-diatom reactions involving two rare gas (Rg) atoms and protons is of crucial importance given the astrophysical relevance of these processes. In a series of previous studies, we have been investigating a number of such Rg(1)+ Rg(2)H+→ Rg(2)+ Rg(1)H+ reactions by means of different numerical approaches. These investigations comprised the construction of accurate potential energy surfaces by means of ab initio calculations.

Insights into the Excited-State Processes in 1-Hydroxy-2-acetonaphthone at ADC(2) and CASSCF Levels.

1-Hydroxy-2-acetonaphthone (HAN) has been extensively studied both experimentally and computationally to ascertain the existence of the excited-state proton transfer process. However, the process of full photocycle including the nonradiative relaxation pathways is yet to be proposed. Therefore, in the present study, we aim at providing a comprehensive picture of the excited-state processes in HAN including the proton transfer and relaxation processes through electronic structure calculations at second-order algebraic diagrammatic construction (ADC(2)) and complete active space second-order perturbation theory (CASPT2)//complete active space self-consistent field (CASSCF) and dynamics simulations at ADC(2) levels.

Assessing the Performance of DFT Functionals for Excited-State Properties of Pyridine-Thiophene Oligomers.

In this article, we have examined the accuracy of various density functional theory (DFT) functionals to reproduce the absorption and CD spectra of pyridine-thiophene oligomers. The performance of different levels of approximations in DFT functionals is discussed with reference to the ADC(2) results. Starting from a linear system, like monomer, calculations are carried out at ADC(2) and DFT levels till a helical system, like pentamer, is formed.

State-to-State Dynamics of the Ne + HeH(+) (v = 0, j = 0) → NeH(+)(v', j') + He Reaction.

The dynamics of the Ne + HeH(+)(v = 0, j = 0) → NeH(+)(v', j') + He reaction was analyzed in detail at the state-to-state level. A time-independent quantum mechanical (TIQM) method was applied to calculate rovibrational distributions and differential cross sections (DCSs), in comparison with quasi-classical trajectory and statistical quantum predictions. Possible changes in the dynamical mechanisms that define the process were also investigated as a function of the collision energy.

Scattering study of the Ne + NeH(+)(v0 = 0, j0 = 0) → NeH(+) + Ne reaction on an ab initio based analytical potential energy surface.

Initial state selected dynamics of the Ne + NeH(+)(v0 = 0, j0 = 0) → NeH(+) + Ne reaction is investigated by quantum and statistical quantum mechanical (SQM) methods on the ground electronic state. The three-body ab initio energies on a set of suitably chosen grid points have been computed at CCSD(T)/aug-cc-PVQZ level and analytically fitted. The fitting of the diatomic potentials, computed at the same level of theory, is performed by spline interpolation.

Structure and optoelectronic properties of helical pyridine-furan, pyridine-pyrrole and pyridine-thiophene oligomers.

Density functional theory based calculations have been carried out to systematically investigate the structural and optoelectronic properties of pyridine-furan, pyridine-pyrrole and pyridine-thiophene oligomers. Comparison of results obtained at B3LYP/6-31G(d) and B3LYP-D3/6-31G(d) levels of theories reveals that the inclusion of dispersion correction with the B3LYP functional has a major impact on ground state structures and stabilities of the most stable conformers, which are helical for our studied systems. Calculation of stabilization energies, gained due to non-bonding interaction between adjacent helical turns, shows that stabilities of helical oligomers increase with an increase in the chain length.

Quantum, Statistical, and Quasiclassical Trajectory Studies For the Ne + HeH(+) → NeH(+) + He Reaction on the Ground Electronic State.

Real wave packet, statistical quantum, and quasiclassical trajectory methods were employed to study the dynamics of Ne + HeH(+)(v0,j0) → He + NeH(+) reaction on an ab initio potential energy surface [J. Phys. Chem.

Wave packet and statistical quantum calculations for the He + NeH⁺ → HeH⁺ + Ne reaction on the ground electronic state.

A real wave packet based time-dependent method and a statistical quantum method have been used to study the He + NeH(+) (v, j) reaction with the reactant in various ro-vibrational states, on a recently calculated ab initio ground state potential energy surface. Both the wave packet and statistical quantum calculations were carried out within the centrifugal sudden approximation as well as using the exact Hamiltonian. Quantum reaction probabilities exhibit dense oscillatory pattern for smaller total angular momentum values, which is a signature of resonances in a complex forming mechanism for the title reaction.

Computational investigation of charge injection and transport properties of a series of thiophene-pyrrole based oligo-azomethines.

The present study explores the structural, charge carrier injection and transport properties of a series of thiophene-pyrrole based oligo-azomethines using density functional theory (DFT) methods. Our findings show that the presence of a bulky substituent adversely affects these properties. However, the electronic effect of substituents may be utilized to tune these properties by substitutions at suitable positions.

Quantum dynamical study of the He + NeH+ reaction on a new analytical potential energy surface.

An analytical potential energy surface (PES) for the ground state of the [HeHNe](+) system has been constructed from a set of 19,605 ab initio data points, obtained from coupled cluster singles and doubles with perturbative triples correction calculations and the aug-cc-pVQZ basis set. The PES is based on the many-body expansion form proposed by Aguado and Paniagua (J. Chem.

Electronically excited states in poly(p-phenylenevinylene): vertical excitations and torsional potentials from high-level ab initio calculations.

Ab initio second-order algebraic diagrammatic construction (ADC(2)) calculations using the resolution of the identity (RI) method have been performed on poly-(p-phenylenevinylene) (PPV) oligomers with chain lengths up to eight phenyl rings. Vertical excitation energies for the four lowest π-π* excitations and geometry relaxation effects for the lowest excited state (S1) are reported. Extrapolation to infinite chain length shows good agreement with analogous data derived from experiment.

A state-to-state dynamical study of the Br + H2 reaction: comparison of quantum and classical trajectory results.

We present a detailed theoretical investigation of the dynamics corresponding to the strongly endothermic Br + H(2) (v = 0-1, j = 0) → H + HBr reaction in the 0.85 to 1.9 eV total energy range.

Cross sections and rate constants for OH + H2 reaction on three different potential energy surfaces for ro-vibrationally excited reagents.

A systematic study of the reagent ro-vibrational excitations in H(2) + OH reaction is presented on three different potential energy surfaces using the multiconfiguration time-dependent Hartree method. An exact form of the kinetic energy operator including Coriolis coupling has been used. Coupled channel results on WDSE surface for vibrational excitation of H(2) produce very large cross sections in accordance with the previous approximate results.

Multiconfiguration time-dependent Hartree approach to study the OH + H2 reaction.

Full dimensional quantum scattering calculations have been carried out for the OH + H(2) --> H(2)O + H reaction on the Walch-Dunning-Schatz-Elgersma and Yang-Zhang-Collins-Lee surfaces employing an exact form of the kinetic energy operator. The multiconfiguration time-dependent Hartree (MCTDH) method has been used to perform the wave packet propagations. The MCTDH method uses relatively little memory and its numerical effort scales much more slowly with the dimensionality of the system compared to conventional propagation methods.

Quantum dynamics of Br + HD reaction.

In this article we report the results of three-dimensional time-dependent quantum wavepacket calculations carried out for the Br + HD( v = 0, j = 0) reaction in the collision energy range 0.0-1.2 eV.

Rovibrational energy transfer in ortho-H2+para-H2 collisions.

We present the results of a full-dimensional quantum mechanical study of the rovibrational energy transfer in the collision between ortho-H2 and para-H2 in the energy range of 0.1-1.0 eV.