A catalyzed / isomerization mechanism of stilbene using -benzoquinone as a triplet sensitizer.

Sensitizer molecules affect not only the quantum yield but also the selectivity of photochemical reactions. For an appropriate design of sensitized photochemical processes, we need to elucidate the reaction mechanism in detail. Here we investigated the mechanism of photoisomerization of stilbene the triplet state with a -benzoquinone sensitizer using density functional theory.

An analysis of valence electronic structure from a viewpoint of resonance theory: Tautomerization of formamide and diazadiboretidine.

The resonance theory is still very useful in understanding the valence electron structure. However, such a viewpoint is not usually obtained by general-purpose quantum chemical calculations, instead requires rather special treatment such as valence bond methods. In this study, we propose a method based on second quantization to analyze the results obtained by general-purpose quantum chemical calculations from the local point of view of electronic structure and analyze diazadiboretidine and the tautomerization of formamide.

Oxidation and Storage Mechanisms for Nitrogen Oxides on Variously Terminated (001) Surfaces of SrFeO and SrFeO Perovskites.

The Ruddlesden-Popper (RP)-type layered perovskite is a candidate material for a new nitrogen oxide (NO) storage catalyst. Here, we investigate the adsorption and oxidation of NO on the (001) surfaces of RP-type oxide SrFeO for all of the terminations by comparing to those of simple perovskite SrFeO by the density functional theory (DFT) calculations. The possible (001) cleavages of SrFeO generate two FeO- and three SrO-terminated surfaces, and the calculated surface energies indicated that the SrO-terminated surface generated by the cleavage at the rock salt layer is the most stable one.

Catalysis of Cu Cluster for NO Reduction by CO: Theoretical Insight into the Reaction Mechanism.

Density functional theory calculations here elucidated that Cu-catalyzed NO reduction by CO occurred not through NO dissociative adsorption but through NO dimerization. NO is adsorbed to two Cu atoms in a bridging manner. NO adsorption energy is much larger than that of CO.

Reaction Behavior of the NO Molecule on the Surface of an M Particle (M = Ru, Rh, Pd, and Ag; = 13 and 55): Theoretical Study of Its Dependence on Transition-Metal Element.

Reaction of NO molecule on M and M clusters (M = Ru, Rh, Pd, and Ag) was theoretically investigated to elucidate why its reaction behavior depends on the position of metal element in the periodic table. DFT computations show that NO dissociative adsorption occurs on M = Ru and Rh, NO molecular adsorption occurs on M = Pd, and NO dimerization occurs on M = Ag, which agree with experimental findings. The d-band center and d-band top become lower in energy following the order Ru > Rh > Pd > Ag; this is one of the characteristic features of the periodic table.

Electronic processes in NO dimerization on Ag and Cu clusters: DFT and MRMP2 studies.

Experimentally observed NO dimerization on Cu and Ag surfaces is surprising because binding energy of NO dimer is very small in gas phase. MRMP2, MP2 to MP4, CCSD(T), and DFT studies of NO dimerization on Ag and Cu clusters disclosed that the CCSD(T) method could be applied to this reaction on Ag and Cu unlike NO dimerization in gas phase which exhibits significantly large nondynamical electron correlation effect. Charge-transfer (CT) from Ag and Cu to NO moieties plays important role in NN bond formation between two NO molecules.

Photophysical properties of fluorescent imaging biological probes of nucleic acids: SAC-CI and TD-DFT Study.

Recently, exciton-controlled hybridization-sensitive fluorescent oligonucleotide (ECHO) probe, which shows strong emission in the near-infrared region via hybridization to the target DNA and/or RNA strand, has been developed. In this work, photophysical properties of the chromophores of these probes and the fluorescent mechanism have been investigated by the SAC-CI and TD-DFT calculations. Three fluorescent cyanine chromophores whose excitation is challenging for TD-DFT methods, have been examined regarding the photo-absorption and emission spectra.

Synthesis and Optical Properties of Excited-State Intramolecular Proton Transfer Active π-Conjugated Benzimidazole Compounds: Influence of Structural Rigidification by Ring Fusion.

Two excited-state intramolecular proton transfer (ESIPT) active benzimidazole derivatives (1 and 2) were synthesized by acid-catalyzed intramolecular cyclization. The steady-state fluorescence spectrum in THF revealed that ring-fused derivative 1 exhibits a dual emission, namely, the major emission was from the K* (keto) form (ESIPT emission) at 515 nm with a large Stokes shift of 11 100 cm and the minor emission was from the E* (enol) form at below 400 nm. In contrast, the normal emission from the E* form was dominant and the fluorescence quantum yield was very low (Φ ∼ 0.

A Theoretical Investigation on CO Oxidation by Single-Atom Catalysts M/γ-AlO (M=Pd, Fe, Co, and Ni).

Single-atom catalysts have attracted much interest recently because of their excellent stability, high catalytic activity, and remarkable atom efficiency. Inspired by the recent experimental discovery of a highly efficient single-atom catalyst Pd/γ-AlO, we conducted a comprehensive DFT study on geometries, stabilities and CO oxidation catalytic activities of M/γ-AlO (M=Pd, Fe, Co, and Ni) by using slab-model. One of the most important results here is that Ni/AlO catalyst exhibits higher activity in CO oxidation than Pd/AlO.

Diels-Alder Cycloaddition of Cyclopentadiene and C at the Extreme High Pressure.

High-pressure Diels-Alder cycloaddition reaction of fullerenes is an important synthetic method for the thermally stable cycloadducts. The effects of high pressure on the potential energy surfaces of Diels-Alder cycloaddition of cyclopentadiene and C were studied with a recently developed approach, the polarizable continuum model for extreme pressure (XP-PCM). It is revealed that the high pressure reduces the activation energies and increases reaction energies drastically, making the DA reaction more favorable.

Comparing the performance of TD-DFT and SAC-CI methods in the description of excited states potential energy surfaces: An excited state proton transfer reaction as case study.

The performances, in the description of excited state potential energy surfaces, of several density functional approximations representative of the currently most applied exchange correlation functionals' families have been tested with respect to post Hartree-Fock references (here Symmetry Adapted Cluster-Configuration Interaction results). An experimentally well-characterized intermolecular proton transfer reaction has been considered as test case. The computed potential energy profiles were analyzed both in the gas phase and in toluene solution, here represented as a polarizable continuum model.

Modeling Molecular Systems at Extreme Pressure by an Extension of the Polarizable Continuum Model (PCM) Based on the Symmetry-Adapted Cluster-Configuration Interaction (SAC-CI) Method: Confined Electronic Excited States of Furan as a Test Case.

Novel molecular photochemistry can be developed by combining high pressure and laser irradiation. For studying such high-pressure effects on the confined electronic ground and excited states, we extend the PCM (polarizable continuum model) SAC (symmetry-adapted cluster) and SAC-CI (SAC-configuration interaction) methods to the PCM-XP (extreme pressure) framework. By using the PCM-XP SAC/SAC-CI method, molecular systems in various electronic states can be confined by polarizable media in a smooth and flexible way.

Projected CAP/SAC-CI method with smooth Voronoi potential for calculating resonance states.

The complex absorbing potential (CAP)/symmetry-adapted cluster-configuration interaction (SAC-CI) method has been combined with a smooth Voronoi potential, which was recently introduced in the extrapolation procedure, to locate π* resonance states of small- to medium-size molecules. Here, the projected CAP/SAC-CI method is combined with this potential and used to calculate the double-bond and heteroaromatic π* resonances of acetaldehyde, butadiene, glyoxal, pyridine, pyrazine, and furan. As observed in the pilot applications, the corrected η-trajectories provide a stable resonance energy and width or lifetime regardless of the size parameter (rcut ) of the smooth Voronoi potential.

Synthesis and Optical Properties of Imidazole- and Benzimidazole-Based Fused π-Conjugated Compounds: Influence of Substituent, Counteranion, and π-Conjugated System.

Fused π-conjugated imidazolium chlorides having hydrogen (1-Cl), octyloxy (2-Cl), N,N-dibutylamino (3-Cl), trifluoromethyl (4-Cl), and cyano (5-Cl) groups substituted on the benzene ring at the 2-position of imidazole were prepared. Counteranion exchanges from chloride to bis(trifluoromethanesulfonyl)imidate (2-TFSI) and tetrafluoroborate (2-BF4) were performed. The optical properties of these compounds (absorption and emission wavelengths, fluorescence quantum yield, and solvatochromism) were influenced by both the substituent and anion character, which was investigated by theoretical calculations using the density functional theory (DFT) and symmetry-adapted cluster-configuration interaction (SAC-CI) methods.

How Can We Understand Au8 Cores and Entangled Ligands of Selenolate- and Thiolate-Protected Gold Nanoclusters Au24(ER)20 and Au20(ER)16 (E = Se, S; R = Ph, Me)? A Theoretical Study.

The geometries and electronic structures of selenolate-protected Au nanoclusters, Au24(SeR)20 and Au20(SeR)16, and their thiolate analogues are theoretically investigated with DFT and SCS-MP2 methods, to elucidate the electronic structure of their unusual Au8 core and the reason why they have the unusual entangled "staple-like" chain ligands. The Au8 core is understood to be an [Au4](2+) dimer in which the [Au4](2+) species has a tetrahedral geometry with a closed-shell singlet ground state. The SCS-MP2 method successfully reproduced the distance between two [Au4](2+) moieties, but the DFT with various functionals failed it, suggesting that the dispersion interaction is crucial between these two [Au4](2+) moieties.

Proton-induced generation of remote N-heterocyclic carbene-Ru complexes.

The proton-induced Ru-C bond variation, which was previously found to be relevant in the water oxidation, has been investigated by using cyclometalated ruthenium complexes with three phenanthroline (phen) isomers. The designed complexes, [Ru(bpy)2 (1,5-phen)](+) ([2](+)), [Ru(bpy)2 (1,6-phen)](+) ([3](+)), and [Ru(bpy)2 (1,7-phen)](+) ([4](+)) were newly synthesized and their structural and electronic properties were analyzed by various spectroscopy and theoretical protocols. Protonation of [4](+) triggered profound electronic structural change to form remote N-heterocyclic carbene (rNHC), whereas protonation of [2](+) and [3](+) did not affect their structures.

An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster-configuration interaction method: the accuracy of excitation energies and intuitive charge-transfer indices.

Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions.

Efficiency of perturbation-selection and its orbital dependence in the SAC-CI calculations for valence excitations of medium-size molecules.

The efficiency and accuracy of the perturbation-selection used in the symmetry-adapted cluster-configuration interaction (SAC-CI) calculations are investigated for several low-lying valence excited states of 21 medium-size molecules, including typical chromophores with heterocyclic macrocycles (free-base porphine, coumarin, indole, and BODIPY), nucleobases, amino acids (tyrosine and tryptophan), polycyclic aromatic hydrocarbons, and organometallics (ferrocene and Re(bpy)(CO)4+1). Benchmark SAC-CI calculations with up to 110 million operators are performed. The efficiency of the perturbation-selection depends on the molecular orbitals (MOs); therefore, the canonical MO and localized MO (LMO) obtained by Pipek-Mezey's method are examined.

Rydberg and π-π* transitions in film surfaces of various kinds of nylons studied by attenuated total reflection far-ultraviolet spectroscopy and quantum chemical calculations: peak shifts in the spectra and their relation to nylon structure and hydrogen bondings.

Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 145-260 nm region were measured for surfaces (thickness 50-200 nm) of various kinds of nylons in cast films to explore their electronic transitions in the FUV region. ATR-FUV spectra show two major bands near 150 and 200 nm in the surface condensed phase of nylons. Transmittance (Tr) spectra were also observed in particular for the analysis of valence excitations.

Benchmark Study on the Triplet Excited-State Geometries and Phosphorescence Energies of Heterocyclic Compounds: Comparison Between TD-PBE0 and SAC-CI.

In this work, we investigated the properties of the triplet excited states of heterocyclic compounds including their geometries, electronic properties, and phosphorescence energies by using both the direct symmetry-adapted cluster-configuration interaction (SAC-CI) method and the TD-DFT approach with the PBE0 exchange-correlation functional (TD-PBE0). The target states are the ππ* and nπ* triplet states of furan, pyrrole, pyridine, p-benzoquinone, uracil, adenine, 9,10-anthraquinone, coumarin, and 1,8-naphthalimide as well as the Rydberg states. The present benchmark demonstrates that these two methods provide reasonably accurate geometries for the excited states of these heterocyclic compounds.

Electronic excitation spectra of molecules in solution calculated using the symmetry-adapted cluster-configuration interaction method in the polarizable continuum model with perturbative approach.

A perturbative approximation of the state specific polarizable continuum model (PCM) symmetry-adapted cluster-configuration interaction (SAC-CI) method is proposed for efficient calculations of the electronic excitations and absorption spectra of molecules in solutions. This first-order PCM SAC-CI method considers the solvent effects on the energies of excited states up to the first-order with using the zeroth-order wavefunctions. This method can avoid the costly iterative procedure of the self-consistent reaction field calculations.

Electronic transitions in liquid amides studied by using attenuated total reflection far-ultraviolet spectroscopy and quantum chemical calculations.

Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 140-260 nm region were measured for several types of liquid amides (formamide, FA; N-methylformamide, NMF; N-methylacetamide, NMA; N,N-dimethylformamide, NdMF; and N,N-dimethylacetamide, NdMA) to investigate their electronic transitions in the FUV region. The spectra were compared with the corresponding gas-phase spectra to examine the shift in the major absorption band in the 180-200 nm region going from the gas phase to the liquid phase, and it was found that the peak shift was dependent on the particular amide. FA and NMF, which exhibit intermolecular C=O[ellipsis.

Chemically intuitive indices for charge-transfer excitation based on SAC-CI and TD-DFT calculations.

A recently proposed charge-transfer (CT) index and some related quantities aimed to the description of CT excitations in push-pull donor-acceptor model systems were computed in vacuum and in ethanol by the direct symmetry-adapted cluster-configuration interaction (SAC-CI) method including solvent effects by means of the nonequilibrium state-specific approach. The effects of both solvation and electron correlations on these quantities were found to be significant. The present results are also in line with previous time-dependent (TD) density functional theory calculations and they demonstrate that SAC-CI provides a description of the excitation character close to that of TD-PBE0.