Theoretical computation of low‐lying electronic states of HCNS: A CASPT2 study

Complete active space self‐consistent field (CASSCF) and complete active space second‐order perturbation theory (CASPT2) calculations in conjunction with the aug‐cc‐pVTZ basis set have been used to investigate the low‐lying electronic states of thiofulminic acid (HCNS), HCNS⁺, and HCNS^?. The result of geometry optimization using CASPT2/aug‐cc‐pVTZ shows that theoretically determined geometric parameters and harmonic vibrational frequencies for the HCNS ground state X¹Σ⁺(X¹A′) are in agreement with previous studies. The ionization energies, the electron affinity energies, the adiabatic excitation energies, and vertical excitation energies have been calculated and the corresponding cation and anion states are identified. By calculating adiabatic electron affinity, the states of HCNS^? have been identified to contain both π orbital states (X²A′ and 1²A″) and dipole‐bond states (1⁴A′ and 1⁴A″). © 2012 Wiley Periodicals, Inc.     

Density functional study of S(N) 2 substitution reactions for CH(3) Cl + CX(1) X(2•-) (X(1) X(2) = HH, HF, HCl, HBr, HI, FF, ClCl, BrBr, and II)

A systematic investigation on the S_N2 displacement reactions of nine carbene radical anions toward the substrate CH₃Cl has been theoretically carried out using the popular density functional theory functional BHandHLYP level with different basis sets 6‐31+G (d, p)/relativistic effective core potential (RECP), 6‐311++G (d, p)/RECP, and aug‐cc‐pVTZ/RECP. The studied models are CX¹X^2?? + CH₃Cl → X²X¹CH₃C^? + Cl^?, with CX¹X^2?? = CH₂^??, CHF^??, CHCl^??, CHBr^??, CHI^??, CF₂^??, CCl₂^??, CBr₂^??, and CI₂^??. The main results are proposed as follows: (a) Based on natural bond orbital (NBO), proton affinity (PA), and ionization energy (IE) analysis, reactant CH₂^?? should be a strongest base among the anion‐containing species (CX¹X^2??) and so more favorable nucleophile. (b) Regardless of frontside attacking pathway or backside one, the S_N2 reaction starts at an identical precomplex whose formation with no barrier. (c) The back‐S_N2 pathway is much more preferred than the front‐S_N2 one in terms of the energy gaps [ΔE(front)?ΔE(back)], steric demand, NBO population analysis. Thus, the back‐S_N2 reaction was discussed in detail. On the one hand, based on the energy barriers (ΔE and ΔE) analysis, we have strongly affirmed that the stabilization of back attacking transition states (b‐TSs) presents increase in the order: b‐TS‐CI₂ < b‐TS‐CBr₂ < b‐TS‐CCl₂ < b‐TS‐CHI < b‐TS‐CHBr < b‐TS‐CHCl < b‐TS‐CF₂ < b‐TS‐CHF < b‐TS‐CH₂. On the other hand, depended on discussions of the correlations of ΔE with influence factors (PA, IE, bond order, and ΔE), we have explored how and to what extent they affect the reactions. Moreover, we have predicted that the less size of substitution (α‐atom) required for the gas‐phase reaction with α‐nucleophile is related to the α‐effect and estimated that the reaction with the stronger PA nucleophile, holding the lighter substituted atom, corresponds to the greater exothermicity given out from reactants to products. © 2012 Wiley Periodicals, Inc. J Comput Chem, 2012     

The UV absorption spectrum and geometry of the HS2 radical

The ultraviolet absorption spectrum of the transient HS₂ radical produced in the flash photolysis of H₂S₂ was recorded. The spectrum observed in the λ = 3070–3800 Å region is assigned to the òA′ ← X²A″ electronic transition, and three progressions to the SS stretching (ν′₁), SSz.sbnd;H bending (ν′₂) and SH stretching (ν′₃) vibrations of the ²A′ upper electronic state. Open-shell CNDO/2 calculations were carried out to optimize the ground state (²A″) molecular geometry. For comparison, similar calculations were also performed on the HO₂ radical. HS₂ is bent in the ground state and nearly linear in the (²A′) and (⁴A″) excited states.     

Synthesis and Characterization of the (5′ → 5″)-Ester of Adenosine 5′-diphosphate with α-D-ribofuranose cyclic 1″,2″-phosphate: A NAD derivative produced during tRNA splicing

The synthesis and spectroscopic properties of the (5′ → 5″)-ester of adenosine 5′-diphosphate with ribofuranose cyclic 1″, 2″-phosphate 3 , a recently discovered metabolite produced during tRNA splicing, are reported.     

A New Phenolic Diglycoside Produced in Response to Copper Toxicity and a New Flavan Dimer from the Leaves of Viburnum ichangense (Hemsl.) Rehd.

A new phenolic digycoside 1 was produced as stress metabolite in the fresh leaves of Viburnum ichangense (Hemsl.) Rehd ., in response to abiotic stress elicitation by CuCl₂. The stress metabolite was characterized as 1‐O‐[α‐L ‐arabinofuranosyl(1→6)‐β‐D ‐glucopyranosyl]‐erythro‐1,2‐bis(4‐hydroxy‐3‐methoxyphenyl)propane‐1,3‐diol ( 1 ). A new flavan dimer, 2,3‐epoxyflavan‐3′,4′,5,7‐tetraol‐(4→8″)‐flavan‐3″,3′′′,4′′′,5′′′,6″‐pentaol ( 2 ), and two known compounds, hovetrichoside A ( 3 ) and asperglaucide ( 4 ), were also isolated. Their structures were established by spectroscopic means.     

Chemiluminescent emissions from the gas phase reactions of ozone with acetylene and allene

Chemiluminescence spectra (300–800 nm) from the reactions of ozone with acetylene and allene have been obtained. These spectra show the production of electronically excited CHO, OH(²Π_i, υ ? 9) and possibly C₂(B³Π_g, υ′ = 0 → X³Π_u, υ″ = 6) from the O₃ + C₂H₂ reaction. CH(²Δ), OH(²Σ⁺) and OH(²Π_j, υ ? 9) emissions were identified from the O₃ + C₃H₄ reaction in addition to the CH₂O(¹A″) emission previously reported.     

CASPT2 and CASSCF studies on the low-lying electronic states of the HCCO radical and its anion

The complete active space self-consistent field and multiconfigurational second-order perturbation theory methods have been used to investigate the low-lying electronic states of the HCCO radical and its anion. The calculated geometrical structure and harmonic vibrational frequencies for the X ²A″ state of HCCO are in good agreement with experimental values. The barrier to 1²П (1²A′) is estimated to be 0.069 eV (554 cm^?1), which is also close to experimental result (540 cm^?1). Moreover, we find that the 2²A′ state is bent, while 2²П (2²A″) is linear. By comparing the oscillator strengths and adiabatic excitation energies, we show that the 2²П (2²A″) ← X ²A″ transition is the most intense among these transitions. The unpaired electrons mainly locate on the C atoms in the 2²A′ and 2²П (2²A″) states according to the Mulliken spin populations. On the other hand, for HCCO^?, the first adiabatic and vertical detachment energies are 2.210 and 2.362 eV, respectively, which reasonably agree with experimental value of 2.338 ± 0.008 eV. Remarkably, we explore several higher excited states of the HCCO radical (1⁴A′, 2⁴A″ and cis-1⁴A′) and its anion (1³A″, 1¹A″ and 1³A′), which have not been reported in previous studies.     

Three new flavonol C-glycosides from Sida cordifolia Linn

Three new flavonol C-glycosides: 3′-(3″,7″-dimethyl-2″,6″-octadiene)-8-C-β-D-glucosyl-kaempferol 3-O-β-D-glucoside (1), 3′-(3″,7″-dimethyl-2″,6″-octadiene)-8-C-β-D-glucosyl-kaempferol 3-O-β-D-glucosyl [1→4]-α-D-glucoside (2) and 6-(3″-methyl-2″-butene)-3′-methoxyl-8-C-β-D-glucosyl-kaempferol 3-O-β-D-glucosyl [1→4]-β-D-glucoside (3) have been isolated from 80% ethanolic extract of the aerial parts of Sida cordifolia Linn followed by partitioning with ethyl acetate. Structures were established by chemical and spectroscopic methods.     

A CASSCF/CASPT2 insight into excited‐state intramolecular proton transfer of four imidazole derivatives

Excited‐state intramolecular proton transfer (ESIPT) of four imidazole derivatives, 2‐(2′‐hydroxyphenyl)imidazole (HPI), 2‐(2′‐hydroxyphenyl)benzimidazole (HPBI), 2‐(2′‐hydroxyphenyl)‐1H‐phenanthro[9,10‐d]imidazole (HPPI) and 2‐(2′‐hydroxyphenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole (HPPPI), were studied by the sophisticated CASSCF/CASPT2 methodology. The state‐averaged SA‐CASSCF method was used to optimize their geometry structures of S₀ and S₁ electronic states, and the CASPT2 calculations were used for the calibration of all the single‐point energies, including the absorption and emission spectra. A reasonable agreement is found between the theoretical predictions and the available experimental spectral data. The forward ESIPT barriers of four target compounds gradually decrease with the increase of molecular size. On the basis of the present calculations, it is a plausible speculation that the larger the size, the faster is the ESIPT rate, and eventually, HPPPI molecule can undergo a completely barrierless ESIPT to the more stable S₁ keto form. Additionally, taking HPI as a representative example, the radiationless decays connecting the S₀ and S₁/S₀ conical intersection structures were also studied by constructing a linearly interpolated internal coordinate (LIIC) reaction path. The qualitative analysis shows that the LIIC barrier of HPI in the keto form is remarkably lower than that of its enol‐form, indicating that the former has a big advantage over the latter in the nonradiative process. © 2015 Wiley Periodicals, Inc.     

Analysis of the stability of finite subspaces in density functional theory

We have studied photodissociation of the A state of the H₂S⁺ ion using the quantum-chemical CAS methods, and the 1² A″ (X ² B ₁) and 1⁴ A″ states are involved in photodissociation of the 1² A′ (A ² A ₁) state (the electronic states in dissociation were studied in the C _s symmetry). The CASPT2 S-loss dissociation potential energy curve (PEC) calculations indicate that the 1² A″ and 1² A′ states correlate with the second limit [H₂ + S⁺(² D)] while the 1⁴ A″ state correlates with the first limit [H₂ + S⁺(⁴S)] and that there are a transition state and a local minimum along the 1² A′ PEC and the repulsive 1⁴ A″ PEC crosses the 1² A″ and 1² A′ PECs. The CASPT2 H-loss dissociation PEC calculations indicate that the 1² A″ and 1⁴ A″ states correlate with the first limit [HS⁺(X ³Σ^?) + H] while the 1² A′ state correlates with the second limit [HS⁺(a ¹Δ) + H] and that the repulsive 1⁴ A″ PEC crosses the 1² A′ PEC. For the crossing doublet and quartet states in pairs, we performed CASSCF minimum energy crossing point (MECP) calculations, and the CASSCF spin-orbit couplings and CASPT2 energies at the MECP geometries were calculated. We examined the two previously proposed mechanisms (mechanisms I and II) for dissociation of the A state to the S⁺ ion, based on our calculation results. We suggest processes for dissociation of the A state to the S⁺ ion (processes I and II, based on mechanisms I and II, respectively) and to the SH⁺ ion (process III) and conclude that photodissociation of the A state mainly leads to the S⁺ ion via the most energetically favorable process II: A ² A ₁ (1² A′) (2.38 eV) → barrier at the linearity (2.96 eV) → X ² B ₁ (1² A″) (0.0 eV) → the 1² A″/1⁴ A″ MECP (3.50 eV, large spin-orbit coupling) → H₂ $ (X^{ 1} \Upsigma_{\text{g}}^{ + } ) $  + S⁺(⁴S) (2.92 eV) (the CASPT2 relative energy values to X ² B ₁ are given in parentheses and the largest value is 3.50 eV at the MECP).     

Are the anions MeO(CO) (n = 1 and 2) methoxide anion donors in the gas phase? A theoretical investigation

• 1. The anions CH₃O‐^–CO and CH₃OCO‐^–CO are both methoxide anion donors. The processes CH₃O‐^–CO → CH₃O^– + CO and CH₃OCO—CO → CH₃O^– + 2CO have ΔG values of +8 and ?68 kJ mol^?1, respectively, at the CCSD(T)/6‐311++G(2d, 2p)//B3LYP/6‐311++G(2d,2p) level of theory.
• 2. The reactions CH₃OCOCO → CH₃OCO + CO (ΔG = ?22 kJ mol^?1) and CH₃COCH(O^–)CO₂CH₃ → CH₃COCH(O^–)OCH₃ + CO (ΔG = +19 kJ mol^?1) proceed directly from the precursor anions via the transition states (CH₃OCO…CO₂)^– and (CH₃COCHO…CH₃OCO)^–, respectively.
• 3. Anion CH₃COCH(O^–)CO₂CH₃ undergoes methoxide anion transfer and loss of two molecules of CO in the reaction sequence CH₃COCH(O^–)CO₂CH₃ → CH₃CH(O^–)COCO₂CH₃ → [CH₃CHO (CH₃OCO‐^–CO)] → CH₃CH(O^–)OCH₃ + 2CO (ΔG = +9 kJ mol^?1). The hydride ion transfer in the first step is a key feature of the reaction sequence.

Copyright © 2010 John Wiley & Sons, Ltd.     

A MS-CASPT2 study of the low-lying electronic excited states of CH2BrCl

The low-lying singlet excited states of CH₂BrCl have been calculated using multiconfigurational CASSCF, second-order perturbation theory CASPT2 and its multistate extension MS-CASPT2. The CASSCF method shows spurious valence–Rydberg mixing and a wrong order of states. Inclusion of dynamical correlation by single root CASPT2 lowers dramatically the energy of the valences states but does not lead to a complete separation between valence and Rydberg states. This situation is improved by the MS-CASPT2 calculations, which gives two valence states for both A^′ and A″ symmetries below the lowest Rydberg state, corresponding to n(Br)→σ^*(C–Br) and n(Cl)→σ^*(C–Cl) transitions at 6.1 eV (203 nm) and 7.2 eV (173 nm), and being repulsive along C–Br and C–Cl coordinates.     

A CAS study on S‐loss and O‐loss dissociation mechanisms of the SO2+ ion in the C,D, and E states

In the present work, we mainly study dissociation of the C ²B₁, D²A₁, and E²B₂ states of the SO₂⁺ ion using the complete active‐space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) methods. We first performed CASPT2 potential energy curve (PEC) calculations for S‐ and O‐loss dissociation from the X, A, B, C, D, and E primarily ionization states and many quartet states. For studying S‐loss predissociation of the C, D, and E states by the quartet states to the first, second, and third S‐loss dissociation limits, the CASSCF minimum energy crossing point (MECP) calculations for the doublet/quartet state pairs were performed, and then the CASPT2 energies and CASSCF spin‐orbit couplings were calculated at the MECPs. Our calculations predict eight S‐loss predissociation processes (via MECPs and transition states) for the C, D, and E states and the energetics for these processes are reported. This study indicates that the C and D states can adiabatically dissociate to the first O‐loss dissociation limit. Our calculations (PEC and MECP) predict a predissociation process for the E state to the first O‐loss limit. Our calculations also predict that the E²B₂ state could dissociate to the first S‐ and O‐loss limits via the A²B₂ ← E²B₂ transition. On the basis of the 13 predicted processes, we discussed the S‐ and O‐loss dissociation mechanisms of the C, D, and E states proposed in the previous experimental studies. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Theoretical prediction on HBeN− and HNBe− anions using multiconfiguration second‐order perturbation theory

The HBeN^? and HNBe^? anions have been investigated for the first time using the CASSCF, CASPT2, and DFT/B3LYP methods with the contracted atomic natural orbital (ANO) and cc‐pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO and B3LYP/cc‐pVTZ levels. The ground and the first excited states of HBeN^? are predicted to be X²Π and A²Σ⁺ states, respectively. It was predicted that the ground state of HNBe^? is X²Σ⁺ state. The A²Π state of HNBe^? has unique imaginary frequency. A bend local minimum M1 was found along the 1²A″ potential energy surface and the A²Π state of HNBe^? should be the transition state of the isomerization reactions for M1 ? M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HBeN bond angle. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

MRD CI study of the photodissociation of HO2 into OH(X2II) + O(3P, 1D)

A MRD CI procedure has been used to calculate several electronic states of the hydroperoxyl radical. The basis set is of double-zeta plus polarization quality augmented with s- and p-type bond and Rydberg functions. The vertical excitation energies of the lowest eight doublet and six quartet states are reported. Oscillator strengths for transitions form the ground to upper doublet states were calculated. A cut of the potential energy surfaces along the OOH fragmentation pathway is used to discuss the mechanisms of HO₂ photodissociation below 6.4 eV. Arguments are presented which indicate O(¹D) rather than O(³P) is the primary dissociation product, and so support the experimental findings rather than theory in the conflict raised earlier on this matter. Ostensibly the dissociation proceeds diabatically on the surface of the initially populated ²A″(1a″ → 2a″) state yielding OH(X²II) + O(¹D).     

Theoretical study of the gas‐phase SN2 reactions of X− with CH3OY (X,Y = Cl,Br, I)

The gas‐phase nucleophilic substitution reactions at saturated oxygen X^? + CH₃OY (X, Y = Cl, Br, I) have been investigated at the level of CCSD(T)/6‐311+G(2df,p)//B3LYP/6‐311+G(2df,p). The calculated results indicate that X^? preferably attacks oxygen atom of CH₃OY via a S_N2 pathway. The central barriers and overall barriers are respectively in good agreement with both the predictions of Marcus equation and its modification, respectively. Central barrier heights (ΔH and ΔH) correlate well with the charges (Q) of the leaving groups (Y), Wiberg bond orders (BO) and the elongation of the bonds (O? Y and O? X) in the transition structures. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Theoretical investigation of the relative stabilities of XSSX and X2SS isomers (X = F,Cl, H,and CH3)

The structures and relative stabilities of a series of disulfide (XSSX) and thiosulfoxide (X₂SS) isomers have been studied for X = F, Cl, CH₃, and H, using various levels of conventional ab initio and density functional theory (DFT). The XSSX isomers are more stable than the X₂SS isomers for all substituents. The energy gap ΔE(X) between the two isomers increases (i.e., XSSX becomes more stable with respect to X₂SS), and the S? S bond contracts in the series for X = F, Cl, CH₃, H. The results are interpreted by means of natural population analysis (NPA) (e.g., the interaction between the disulfide moiety S and the two substituents X·). The bonding in the hypervalent X₂SS species is similar to the bonding in the nonhypervalent XSSX and does not involve a special role for sulfur-3d orbitals. These orbitals acquire only minimal populations and are not to be conceived as valence orbitals. The DFT and conventional ab initio results, Xα/DZP and MP2/6-31G** optimized structures and isomerization energies (at the highest levels of both methods), agree well. © 1995 by John Wiley & Sons, Inc.     

Assignment on the X,A, B,C, and D states of the C6H5Br+ cation based on high‐level calculations

Geometries, frequencies, and energies of the 1²B₁, 1²A₂, 1²B₂, 2²B₁, 2²B₂, and 1²A₁, of the C₆H₅Br⁺ ion were calculated by using CASSCF and CASPT2 methods in conjunction with an ANO‐RCC basis. The CASPT2//CASSCF adiabatic excitation energies and CASPT2 relative energies for the six states are in good agreement with experiment. The X, A, B, C, and D electronic states of the C₆H₅Br⁺ ion were assigned to be X²B₁, A²A₂, B²B₂, C²B₁, and D²B₂ based on the CASSCF and CASPT2 calculations. The assignment on the D state of the C₆H₅Br⁺ ion is different from the previously published works. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Syntheses and electroluminescence properties of conjugated poly(p‐phenylene vinylene) derivatives bearing dendritic pendants

A series of new poly(p‐phenylene vinylene) derivatives with different dendritic pendants—poly{2‐[3′,5′‐bis(2″‐ethylhexyloxy)benzyloxy]‐1,4‐phenylenevinylene} (BE–PPV), poly{2‐[3′,5′‐bis(3″,7″‐dimethyl)octyloxy]‐1,4‐phenylenevinylene} (BD–PPV), poly(2‐{3′,5′‐bis[3″,5″‐bis(2?‐ethylhexyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene) (BBE–PPV), poly(2‐{3′,5′‐bis[3″,5″‐bis(3?,7?‐dimethyloctyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene) (BBD–PPV), and poly[(2‐{3′,5′‐bis[3″,5″‐bis(2?‐ethylhexyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene)‐co‐(2‐{3′,5′‐bis[3″,5″‐bis(3?,7?‐dimethyloctyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene)] (BBE‐co‐BBD–PPV; 1:1)—were successfully synthesized according to the Gilch route. The structures and properties of the monomers and the resulting conjugated polymers were characterized with ¹H and ¹³C NMR, elemental analysis, gel permeation chromatography, thermogravimetric analysis, ultraviolet–visible absorption spectroscopy, photoluminescence, and electroluminescence spectroscopy. The obtained polymers possessed excellent solubility in common solvents and good thermal stability, with a 5% weight loss temperature of more than 328 °C. The weight‐average molecular weights and polydispersity indices of BE–PPV, BD–PPV, BBE–PPV, BBD–PPV, and BBE‐co‐BBD–PPV (1:1) were in the range of 1.33–2.28 × 10⁵ and 1.35–1.53, respectively. Double‐layer light‐emitting diodes (LEDs) with the configuration of indium tin oxide/polymer/tris(8‐hydroxyquinoline) aluminum/Mg:Ag/Ag devices were fabricated, and they emitted green‐yellow light. The turn‐on voltages of BE–PPV, BD–PPV, BBE–PPV, BBD–PPV, and BBE‐co‐BBD–PPV (1:1) were approximately 5.6, 5.9, 5.5, 5.2, and 4.8 V, respectively. The LED devices of BE–PPV and BD–PPV possessed the highest electroluminescent performance; they exhibited maximum luminance with about 860 cd/m² at 12.8 V and 651 cd/m² at 13 V, respectively. The maximum luminescence efficiency of BE–PPV and BD–PPV was in the range of 0.37–0.40 cd/A. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3126–3140, 2005