Dynamic Symmetry Breaking Hidden in Fano Resonance of a Molecule: S1 State of Diazirine Using Quantum Wave Packet Propagation.

Fano resonance in the predissociation of the S1 state of diazirine was studied by applying a time-dependent wave packet propagation method, and dynamic symmetry breaking (DSB) around the stationary structure of S1 was disclosed in a detailed analysis of this theoretical result. The DSB was found to originate in coupling between the asymmetric C-N2 stretching and CH2 wagging modes, suggesting that there is a slight time gap between ring opening and the concurrent dragging of two H atoms of the CH2 moiety. Although the depth of the double well due to DSB is just 0.011 eV, its presence noticeably affects the early time dynamics and observed spectrum.

Prediction of the reduction potential of tris(2,2'-bipyridinyl)iron(III/II) derivatives.

The reduction potentials of a tris(2,2'-bipyridinyl)iron (III/II) and iron(III/II) couples complexed with 2,2'-bipyridinyl derivatives in acetonitrile are predicted using density functional theory. The calculation protocol proposed by Kim et al. (Kim, J. Park, Y. S. Lee, J. Comput. Chem. 2013, 34, 2233) showing reliable performance for the reduction potential is used. The four kinds of the functional groups, a methoxy group, a methyl group, a chlorine atom, and a cyanide group, are substituted at the ligands to examine the electronic effect on the reduction potential. Electron donating/withdrawing effect is analyzed by comparing the reduction potential having different substituents at the same position. The influence of the geometrical strain on the reduction potential is investigated. The good correlation between the experimental results and the calculated results is obtained. Not only the general trend, but also the detailed phenomena are correctly reproduced. The maximum deviation from the experimental value is 0.083 V for the methyl substitution at the position 4. The mean absolute error for the seven couples is 0.047 V. The difference of the reduction potential between the chlorine atom substituted at the positions 4 and 5, 0.1 V, is well described. The difference between the CN and the Cl substitution of 0.318 and 0.228 V for the position 4 and 5 is correctly obtained as 0.325 and 0.213 V, respectively. The simple linear relation between the lowest unoccupied molecular orbital (LUMO) energy of the Fe(III) complexes in solution and the calculated reduction potentials is obtained with the R(2) of 0.977.

Factors Affecting the Branching Ratio of Photodissociation: Thiophenol Studied through Quantum Wavepacket Dynamics.

The photodissociation dynamics of thiophenol (PhSH) excited to the 1(1) ππ* state was investigated by time-dependent quantum wavepacket propagation within two-dimensional (2D) space consisting of the S-H bond and -SH torsion. We systematically studied the dependence of the branching ratio (Ã/X(~)) between the two electronic states of the phenylthiyl radical (PhS(.) ) on several factors of the 2D potential energy surfaces (PESs). The effect of a reduced initial barrier to the first ππ*/πσ* conical intersection (CI) was found to be marginal, whereas the effects of a reduced torsional barrier of -SH on the excited ππ* state and the mitigated slope of the πσ* PES between the first (ππ*/πσ*) and the second (πσ*/S0 ) CIs were noticeable. The effect of the slope on the branching ratio has never been previously noticed. It was shown that the branching ratio can be sufficiently above unity without pre-excitation of the torsion mode of -SH, which has been assumed so far.

Heteroleptic cyclometalated iridium(III) complexes supported by triarylborylpicolinate ligand: ratiometric turn-on phosphorescence response upon fluoride binding.

Heteroleptic cyclometalated iridium(III) complexes (C^N)2Ir(Bpic) (4-6) (C^N = dfppy (4), ppy (5), btp (6)) supported by triarylborylpicolinate (Bpic) ancillary ligand were synthesized and characterized. X-ray diffraction study of 5 confirmed N^O chelation of the Bpic ligand to the iridium center forming an (C^N)2Ir-borane conjugate. While the UV/vis absorption bands of 4-6 remained almost unchanged in the low-energy region upon fluoride addition, a ratiometric turn-on phosphorescence response was observed for 4 and 5. In contrast, the phosphorescence of 6 was little affected by fluoride binding. Experimental and theoretical studies suggest that the LUMO in neutral 4 and 5 is dominated by the Bpic ligand, which makes the weakly emissive (3)ML'CT/(3)LL'CT (L = C^N; L' = Bpic) states as the lowest-energy triplet excited state, while the fluoride binding to 4 and 5 induces the highly emissive (3)MLCT/(3)ππ* states centered on the (C^N)2Ir moiety. Thermally induced conversion from the (3)MLCT/(3)ππ* to the (3)ML'CT/(3)LL'CT states is suggested to be responsible for the low-energy weak phosphorescence in 4 and 5.

Deep red phosphorescence of cyclometalated iridium complexes by o-carborane substitution.

Heteroleptic (C(∧)N)2Ir(acac) (C(∧)N = 5-MeCBbtp (5a); 4-BuCBbtp (5b); 5-BuCBbtp (5c); 5-(R)CBbtp = 2-(2'-benzothienyl)-5-(2-R-ortho-carboran-1-yl)-pyridinato-C(2),N, R = Me and n-Bu; 4-BuCBbtp = 2-(2'-benzothienyl)-4-(2-n-Bu-ortho-carboran-1-yl)-pyridinato-C(2),N, acac = acetylacetonate) complexes supported by o-carborane substituted C(∧)N-chelating ligand were prepared, and the crystal structures of 5a and 5b were determined by X-ray diffraction. While 5a and 5c exhibit a deep red phosphorescence band centered at 644 nm, which is substantially red-shifted compared to that of unsubstituted (btp)2Ir(acac) (6) (λem = 612 nm), 5b is nonemissive in THF solution at room temperature. In contrast, all complexes are emissive at 77 K and in the solid state. Electrochemical and theoretical studies suggest that the carborane substitution leads to the lowering of both the HOMO and LUMO levels, but has higher impact on the LUMO stabilization than the HOMO, resulting in the reduction of the triplet excited state energy. In particular, the LUMO stabilization in the 4-substituted 5b is more contributed by carborane than that in the 5-substituted 5a. The solution-processed electroluminescent device incorporating 5a as an emitter displayed deep red phosphorescence (CIE coordinate: 0.693, 0.290) with moderate performance (max ηEQE = 3.8%) whereas the device incorporating 5b showed poor performance, as well as weak luminance.

Two-component multi-configurational second-order perturbation theory with Kramers restricted complete active space self-consistent field reference function and spin-orbit relativistic effective core potential.

We report the formulation and implementation of KRCASPT2, a two-component multi-configurational second-order perturbation theory based on Kramers restricted complete active space self-consistent field (KRCASSCF) reference function, in the framework of the spin-orbit relativistic effective core potential. The zeroth-order Hamiltonian is defined as the sum of nondiagonal one-electron operators with generalized two-component Fock matrix elements as scalar factors. The Kramers symmetry within the zeroth-order Hamiltonian is maintained via the use of a state-averaged density, allowing a consistent treatment of degenerate states. The explicit expressions are derived for the matrix elements of the zeroth-order Hamiltonian as well as for the perturbation vector. The use of a fully variational reference function and nondiagonal operators in relativistic multi-configurational perturbation theory is reported for the first time. A series of initial calculations are performed on the ionization potential and excitation energies of the atoms of the 6p-block; the results display a significant improvement over those from KRCASSCF, showing a closer agreement with experimental results. Accurate atomic properties of the superheavy elements of the 7p-block are also presented, and the electronic structures of the low-lying excited states are compared with those of their lighter homologues.

A protocol to evaluate one electron redox potential for iron complexes.

Density functional theory calculation has been performed to calculate the redox potential and the correct ground spin state of iron complexes in acetonitrile. Widely used B3LYP functional is applied with the spin state corrected basis sets. The newly developed protocol for the set of 21 iron complexes is to optimize the structure at the level of the B3LYP/6-31G* and to calculate the single point electronic energy with the same functional and the modified basis sets s6-31G* for the iron atom and 6-31+G* for other ligand atoms. The solvation energy is considered through the polarized continuum model and the cavity creation energy is included for the accurate spin state description. Modifying the cavity size by employing the different scaling factor according to the mean absolute value of the natural population analysis charge (MA-NPA) is introduced. The molecule with the large MA-NPA requires the cavity size smaller than the less polar one. This protocol gives only 1 wrong ground spin state among the 18 iron complexes for which experimental data are known. For the open circuit voltage (OCV) calculation, our protocol performs well yielding the mean absolute error of 0.112 V for the test set. The close correlation between the calculated and the experimental OCV are obtained.

Phosphorescence color tuning of cyclometalated iridium complexes by o-carborane substitution.

Heteroleptic (C(^)N)(2)Ir(acac) (C(^)N = 4-CBppy (1); 5-CBppy (2), 4-fppy (4) CB = ortho-methylcarborane; ppy = 2-phenylpyridinato-C(2),N, 4-fppy = 2-(4-fluorophenyl)pyridinato-C(2),N, acac = acetylacetonate) complexes were prepared and characterized. While 1 exhibits a phosphorescence band centered at 531 nm, which is red-shifted compared to that of unsubstituted (ppy)(2)Ir(acac) (3) (λ(em) = 516 nm), the emission spectrum of 2 shows a blue-shifted band at 503 nm. Comparison with the emission band for the 4-fluoro-substituted 4 (λ(em) = 493 nm) indicates a substantial bathochromic shift in 1. Electrochemical and theoretical studies suggest that while carborane substitution on the 4-position of the phenyl ring lowers the (3)MLCT energy by a large contribution to lowest unoccupied molecular orbital (LUMO) delocalization, which in turn assigns the lowest triplet state of 1 as [d(π)(Ir)→π*(C(^)N)] (3)MLCT in character, the substitution on the 5-position raises the (3)MLCT energy by the effective stabilization of the highest occupied molecular orbital (HOMO) level because of the strong inductive effect of carborane. An electroluminescent device incorporating 1 as an emitter displayed overall good performance in terms of external quantum efficiency (6.6%) and power efficiency (10.7 lm/W) with green phosphorescence.

Novel reversible Zn2+-assisted biological phosphate "turn-on" probing through stable aryl-hydrazone salicylaldimine conjugation that attenuates ligand hydrolysis.

A novel reversible zinc(II) chemosensing ensemble (2·Zn(2+)) allows for selective "turn-on" fluorescence sensing of ATP and PPi in aqueous media (detection limits: 2.4 and 1.0 µM, respectively) giving selective binding patterns: ATP ∼ PPi > ADP ≫ AMP > monophosphates ≈ remaining ions tested. The conjugated hydrazone [C═N-NH-R] resists hydrolysis considerably, compared to the imine [C═N-CH2-R, pyridin-2-ylmethanamine] functionality, and generalizes to other chemosensing efforts. Prerequisite Zn(2+)·[O(phenol)N(imine)N(pyr)] binding is selective, as determined by UV-vis and NMR spectroscopy; ATP or PPi extracts Zn(2+) to regenerate the ligand-fluorophore conjugate (PPi: turn-on, 512 nm; detection limit, 1.0 µM). Crystallography, 2-D NMR spectroscopy, and DFT determinations (B3LYP/631g*) support the nature of compound 2. 2-Hydrazinyl-pyridine-salicylaldehyde conjugation is unknown, as such; a paucity of chemosensing-Zn(2+) binding reports underscores the novelty of this modifiable dual cation/anion detection platform. A combined theoretical and experimental approach reported here allows us to determine both the potential uniqueness as well as drawbacks of this novel conjugation.

Two-component Kramers restricted complete active space self-consistent field method with relativistic effective core potential revisited: theory, implementation, and applications to spin-orbit splitting of lower p-block atoms.

The relativistic two-component complete active space self-consistent field theory in Kramers restricted formalism (KRCASSCF) through the framework of the spin-orbit relativistic effective core potential is implemented into the KPACK package. This paper continues the development previously reported [Y. S. Kim and Y. S. Lee, J. Chem. Phys. 119, 12169 (2003)] and extends the theory by means of adding time-reversal symmetry into the relevant expressions so as to complete the course of theoretical development. We retained the usage of elementary spinor excitation operator for defining the spinor rotation operator and derived the gradient and Hessian in simpler forms than previously found. To eliminate redundant computation resulting from repeating sums in the derivatives, a suitable decomposition method is proposed, which also facilitates the implementation. The two-step near second-order approach is employed for convergence. The present implementation is applicable for both closed- and open-shell systems and is used to calculate the atoms of lower p-block. The results for 5p and 6p are in good agreement with the experiments, and those for 7p are comparable to multi-reference configuration interaction results, showing that KRCASSCF is a versatile tool for the relativistic electronic structure calculation of molecules containing moderate-weight through superheavy elements.

Nuclear motion captured by the slow electron velocity imaging technique in the tunnelling predissociation of the S1 methylamine.

Predissociation dynamics of methylamines (CH(3)NH(2) and CH(3)ND(2)) on the first electronically excited states are studied using the slow-electron velocity imaging method to unravel the multi-dimensional nature of the N-H(D) chemical bond dissociation reaction which occurs via tunnelling. The nearly free internal rotation around the C-N bond axis is found to be strongly coupled to the reaction pathway, revealing nuclear motions actively involved in the tunnelling process on the S(1) potential energy surfaces. The vibrational state-resolved energy and angular distributions of photoelectron, ejected from the ionization mediated by the metastable intermediate S(1) state provide a unique way for mapping the predissociative potential energy surfaces.

Ambient carbon dioxide capture by boron-rich boron nitride nanotube.

Carbon dioxides (CO(2)) emitted from large-scale coal-fired power stations or industrial manufacturing plants have to be properly captured to minimize environmental side effects. From results of ab initio calculations using plane waves [PAW-PBE] and localized atomic orbitals [ONIOM(wB97X-D/6-31G*:AM1)], we report strong CO(2) adsorption on boron antisite (B(N)) in boron-rich boron nitride nanotube (BNNT). We have identified two adsorption states: (1) A linear CO(2) molecule is physically adsorbed on the B(N), showing electron donation from the CO(2) lone-pair states to the B(N) double-acceptor state, and (2) the physisorbed CO(2) undergoes a carboxylate-like structural distortion and C═O π-bond breaking due to electron back-donation from B(N) to CO(2). The CO(2) chemisorption energy on B(N) is almost independent of tube diameter and, more importantly, higher than the standard free energy of gaseous CO(2) at room temperature. This implies that boron-rich BNNT could capture CO(2) effectively at ambient conditions.

Electronic and chelation effects on the unusual C2-methylation of N-(para-substituted)phenylaziridines with lithium organocuprates.

Density functional theory calculations with the B3LYP functional were performed for the title ring-opening reaction to understand the intrinsic activating and directing effects of the N-substituents, as well as the electron donating effect of the para-substituted (Y = Cl, H, Me) phenyl group at the more hindered benzylic C2 atom. The N-tosyl group (i.e., N-Tos) or the N-(2-pyridyl)sulfonyl group (i.e., N-Py) was introduced to activate the ring nitrogen atom (N1) and the para-substituted (Y = Cl, H, Me) phenyl group for the activation of the C2 atom. Conformational searches and geometry optimizations were performed for the N-(para-substituted)phenylaziridines (1∼6). Calculations indicate that the aziridine 6 (i.e., Py/Me) has the most elongated C2-N1 bond intrinsically due to the electronic activating effects, implying the aziridine 6 to be the most potent candidate for the more-hindered C2 opening. Transition states (TSs) were investigated for the prospective ring-opening paths (I∼IV), considering the types of intermolecular push-pull interactions between the N-activated phenylaziridines and the cuprate. The N-Py group provides an unique C2-favored TS along the path IV, which the N-Tos group cannot afford, due to the less charge transfer from the nucleophilic CH 3δ- of the cuprate into the electrophilic C2 atom. Furthermore, the e-donating effect of the para-substituents (Y = Cl, H, Me) enhances the C2 opening for the path IV. This study enables us to understand the unusual ring-opening phenomena in terms of electronic and directing effects and hence may serve as a tool to design substrates for highly regioselective ring openings.

Control of on-off or off-on fluorescent and optical [Cu²âº] and [Hg²âº] responses via formal Me/H substitution in fully characterized thienyl "scorpionate"-like BODIPY systems.

One 8-phenyl and two 8-mesityl-substituted "scorpionate"-like BODIPY-type species of the formula [3,4,4-tris(5-R-(2-thienyl))-8-(2,4,6-R'-phenyl)-4-bora-3a,4a-diaza-s-indacene (R = H, R' = H, 3a; R, = H, R' = Me, 2a; R, = Me, R' = Me, 2b)] have been synthesized and fully characterized. Importantly, differences in their solution (MeCN) optical Cu(2+) and Hg(2+) probing capacity via SSS-chelation were investigated. Compounds 2a-3a were prepared from the requisite 8-substituted BODIPY complexes. They were characterized first by complete (1)H, (11)B and (13)C NMR spectroscopic assignments (CD(3)Cl or CD(3)C(O)CD(3)); the molecular structures of 2a and 3a were determined by X-ray crystallography. Compounds 2a-3a were studied by UV-vis and fluorescence spectroscopy [Φ(F) = 0.27 ± 0.013 (2a); 0.024 ± 0.0016 (2b); 0.0034 ± 0.00047 (3a)]. Importantly, low [Cu(2+)] with 3a (<3.0 × 10(-5) M) gave rise to an increase of fluorescence intensity (off-on; 6.3-fold), whereas with 2a it decreased (on-off). When [Hg(2+)] (<3.0 × 10(-5) M) was added to 2b, the λ(em,max) value increased (off-on; 3.2-fold), and for 2a, it decreased (on-off). The association constant (K(a)) for Hg(2+)·2a was determined to be 3120 ± 307 M(-1). An approximate stoichiometric 1:1 binding determined by Job plot analysis is in line with successful DFT modeling of SSS-Cu(2+) binding for this system type. (1)H NMR spectroscopy also revealed tentative sets of product complex peaks. These simple differences caused by formal ligand Me-group incorporation are the first for any related fluorophores, to the best of our knowledge.

Molecular structures, energetics, and electronic properties of neutral and charged Hg(n) clusters (n = 2-8).

The geometric and electronic structures of small mercury clusters, Hg(n), Hg(n)(+), and Hg(n)(-) (n

Spin-orbit density functional and ab initio study of HgX(n) (X=F, Cl, Br, and I; n=1, 2, and 4).

Quantum chemical calculations of HgX(n) (X=F, Cl, Br, and I; n=1, 2, and 4) in the gas phase are performed using the density functional theory (DFT), two-component spin-orbit (SO) DFT, and high-level ab initio method with relativistic effective core potentials (RECPs). Molecular geometries, vibrational frequencies, and various thermochemical energies are calculated and compared with available experimental results. We assess the performances of DFT functionals for calculating various molecular properties. The PBE0 functional is generally reasonable for the molecular geometries and the vibrational frequencies, but the M06 functional is more appropriate for estimating thermochemical energies. Both shape-consistent and energy-consistent RECPs correctly describe the SO effect.

Consequences of a linear two-coordinate geometry for the orbital magnetism and Jahn-Teller distortion behavior of the high spin iron(II) complex Fe[N(t-Bu)2]2.

Mossbauer, EPR, magnetic susceptibility, and DFT studies of the unusual two-coordinate iron(II) amide Fe[N(t-Bu)(2)](2) show that it retains a linear N-Fe-N framework due to the nonbonding delta nature of the (xy, x(2)-y(2)) orbitals. The resulting near-degenerate ground state gives rise to a large magnetic moment and a remarkably large internal hyperfine field. The results confirm that extraordinary orbital magnetic effects can arise in linear transition metal complexes in which orbital degeneracies are not broken by Jahn-Teller or Renner-Teller distortions.

Synthesis and properties of salen-aluminum complexes as a novel class of color-tunable luminophores.

Showing their true colors? Full emission color tuning in the visible region can be achieved with salen-aluminum complexes that are electronically modulated at C5 of the phenoxide ring in the salen moiety. Emission spectra for various substituents R(5) are shown (EWG: electron-withdrawing group, EDG: electron-donating group).A series of salen-aluminum complexes, [{(R(5))(2)-salen(3-tBu)(2)}Al(OC(6)H(4)-p-C(6)H(5))] (salen=N,N'-bis(salicylidene)ethylenediamine; R(5)=H (1), tBu (2), Br (3), Ph (4), OMe (5), NMe(2) (6)) and [{5,5'-(NMe(3))(2)-salen(3-tBu)(2)}Al(OC(6)H(4)-p-C(6)H(5))][OTf](2) (7; OTf=CF(3)SO(3)) that are electronically modulated directly at C5 of the phenoxide ring in the salen moiety has been prepared. The crystal structures of 1, 4, 6, and 7 determined by X-ray diffraction reveal distorted square-pyramidal geometries around the Al atoms. Complexes 1-7 are all air-stable in both the solid and solution states and have high thermal stability (decomp 313-338 degrees C). Differential scanning calorimetric analyses show that they can form amorphous glasses with glass transition temperatures of 95-132 degrees C depending on the C5 substituent. UV/Vis absorption spectra of the complexes exhibit major bands at lambda=338-413 nm assignable to salen-centered pi-pi* transitions with a gradual red shift of the absorption maximum wavelengths as the substituent is varied from an electron-withdrawing (NMe(3)) to an electron-donating group (NMe(2)). The maxima in the emission spectra of 1-7 occur over the entire visible region, ranging from lambda=438 nm for 7 to lambda=599 nm for 6, with high fluorescence quantum efficiencies of up to Phi=0.40 for 4 in solution. DFT calculations suggest that the low-energy electronic transitions in 1-7 are characterized by HOMO(-i)-LUMO(+1) (i=1 for 1-6 or i=4 for 7) transitions localized on the salen moiety, with much involvement of the C5 position in the HOMO(-i). Thus, the electronic alteration at the C5 position of the phenoxide ring, which mainly affects the HOMO(-i) energy levels of salen-Al luminophores, is responsible for the observed emission color-tuning properties over the entire visible region.

Photodissociation dynamics of thiophenol-d1: the nature of excited electronic states along the S-D bond dissociation coordinate.

The S-D bond dissociation dynamics of thiophenol-d1 (C6H5SD) pumped at 266, 243, and 224 nm are examined using the velocity map ion imaging technique. At both 266 and 243 nm, distinct peaks associated with X and A states of the phenylthiyl radical (C6H5S*) are observed in the D+ image at high and low kinetic energy regions, respectively. The partitioning of the available energy into the vibrational energy of the phenylthiyl radical is found to be enhanced much more strongly at 266 nm compared to that at 243 nm. This indicates that the pipi* electronic excitation at 266 nm is accompanied by significant vibrational excitation. Given the relatively large anisotropy parameter of -0.6, the S-D dissociation at 266 nm is prompt and should involve the efficient coupling to the upper-lying n(pi)sigma* repulsive potential energy surface. The optical excitation of thiophenol at 224 nm is tentatively assigned to the pisigma* transition, which leads to the fast dissociation on the repulsive potential energy surface along the S-D coordinate. The nature of the electronic transitions associated with UV absorption bands is investigated with high-level ab initio calculations. Excitations to different electronic states of thiophenol result in unique branching ratios and vibrational excitations for the fragment of the phenylthiyl radical in the two lowest electronic states.

Influence of phenolic hydroxyl groups on second-order optical nonlinearity at an example of 2,4- and 3,4-dihydroxyl hydrazone isomorphic crystals.

We investigate the crystal structure and physical properties of 2,4- and 3,4-dihydroxybenzaldehyde-4-nitrophenylhydrazone (DHNPH) isomer crystals to understand the relation between molecular ordering with noncovalent interactions based on phenolic OH groups. The microscopic and macroscopic optical nonlinearities of 2,4- and 3,4-DHNPH crystals are investigated experimentally and theoretically by using density functional theory calculations. Although the two isomer crystals possess a very similar molecular orientation based on a similar supramolecular synthon, 2,4-DHNPH exhibits a 1.7 times larger powder second harmonic generation efficiency than 3,4-DHNPH, which is attributed to their different intermolecular interactions involving phenolic OH groups. We show that the microscopic nonlinearity of the DHNPH molecules is particularly sensitive to variations in phenolic OH characteristics such as the orientation and intermolecular interactions.