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The micropipet delivery--substrate collection (MD--SC) mode of scanning electrochemical microscopy (SECM) is demonstrated. This new mode is intended for the study and imaging of electrochemical as well as electrocatalytic reactions of neutral species that cannot be generated electrochemically. The spontaneous transfer of the analyte from an organic solvent across an interface between two immiscible electrolyte solutions (ITIES) and its diffusion into the aqueous solution served as the mechanism to deliver it to the substrate, where the corresponding electrochemical or electrocatalytic reaction is carried out. High-resolution SECM images of ferrocenemethanol (FcMeOH) oxidation, benzoquinone (BQ) reduction, and the formic acid oxidation reaction (FAOR) at a Pt microelectrode substrate were successfully acquired. Furthermore, this new mode was used for the screening of electrocatalyst arrays for the methanol oxidation reaction (MOR), with the optimization of an efficient candidate, [Pt.sub.80][Ce.sub.20]. Digital simulations produced quantitative information about the expected current response at the substrate in the proposed MD--SC mode of SECM. 10.1021/ac901434a

The electrochemical oxidation of formic acid was studied by the tip generation-substrate collection (TG-SC) mode of scanning electrochemical microscopy (SECM), extending the number of applications of SECM in electrocatalysis. Formic acid was generated at a Hg on Au ultramicroelectrode (UME) tip by reduction of C[O.sub.2] in a 0.1 M KHC[O.sub.3] solution saturated with this gas. The electrocatalytic activity of different Pd-Co bimetallic compositions was evaluated using a Pd-Co electrocatalyst array formed by spots deposited onto glassy carbon (GC) as a SECM substrate. The SECM tip, which generated a constant formic acid flux, was scanned above the array and the oxidation current generated when formic acid was collected by active electrocatalyric spots was displayed as a function of tip position. This generated a SECM image that showed the electrocatalytic activity of each spot. SECM screening identified [Pd.sub.50][Co.sub.50] (Pd/Co = 50:50, atomic ratio) as a better electrocatalyst toward the formic acid oxidation than pure Pd or Pt in 0.1 M KHC[O.sub.3] solution and this result was confirmed by cyclic voltammetry. Positive feedback was observed for the most active compositions of Pd-Co which suggests fast reaction kinetics and chemical reversibility during the oxidation of formic acid to C[O.sub.2]. Moreover this feedback increases the contrast between active and non-active spots in this imaging mode.

The clean electrochemical oxidation of the furan moiety in oligoaryls to obtain corresponding enediones in excellent yield is reported. The furan-containing oligoaryls could be used as hole transporting materials for optoelectronic applications.

The micropipet delivery-substrate collection (MD-SC) mode of scanning electrochemical microscopy (SECM) is demonstrated. This new mode is intended for the study and imaging of electrochemical as well as electrocatalytic reactions of neutral species that cannot be generated electrochemically. The spontaneous transfer of the analyte from an organic solvent across an interface between two immiscible electrolyte solutions (ITIES) and its diffusion into the aqueous solution served as the mechanism to deliver it to the substrate, where the corresponding electrochemical or electrocatalytic reaction is carried out. High-resolution SECM images of ferrocenemethanol (FcMeOH) oxidation, benzoquinone (BQ) reduction, and the formic acid oxidation reaction (FAOR) at a Pt microelectrode substrate were successfully acquired. Furthermore, this new mode was used for the screening of electrocatalyst arrays for the methanol oxidation reaction (MOR), with the optimization of an efficient candidate, Pt80Ce20. Digital simulations produced quantitative infonnation about the expected current response at the substrate in the proposed MD–SC mode of SECM. [ABSTRACT FROM AUTHOR]

A strategy for the synthesis of dibenz[ a , j ]anthracenes (DBAs) from cyclohexa-2,5-diene-1-carboxylic acids is presented. Our approach involves sequential C-H olefination, cycloaddition, and decarboxylative aromatization. In the key step for DBA skeleton construction, the bis-C-H olefination products, 1,3-dienes, are utilized as substrates for [4 + 2] cycloaddition with benzyne. This concise synthetic route allows for regioselective ring formation and functional group introduction. The structural features and photophysical properties of the resulting DBA molecules are discussed.

A study of the intensity-borrowing mechanisms important to optical cycling transitions in laser-coolable polyatomic molecules arising from non-adiabatic coupling, contributions beyond the Franck-Condon approximation, and Fermi resonances is reported. It has been shown to be necessary to include non-adiabatic coupling to obtain computational accuracy that is sufficient to be useful for laser cooling of molecules. The predicted vibronic branching ratios using perturbation theory based on the non-adiabatic mechanisms have been demonstrated to agree well with those obtained from variational discrete variable representation calculations for representative molecules including CaOH, SrOH, and YbOH. The electron-correlation and basis-set effects on the calculated transition properties, including the vibronic coupling constants, the spin-orbit coupling matrix elements, and the transition dipole moments, and on the calculated branching ratios have been thoroughly studied. The vibronic branching ratios predicted using the present methodologies demonstrate that RaOH is a promising radioactive molecule candidate for laser cooling.

An asymmetric double oxidative [3 + 2] cycloaddition is reported. Oxidation of 3-((2,2,2-trifluoroethyl)amino)indolin-2-ones and β-aryl-substituted aldehydes simultaneously and subsequent asymmetric cycloaddition in the presence of the chiral amino catalyst generated highly functionalized chiral CF 3 -containing spiro[pyrrolidin-3,2'-oxindole] with four contiguous stereocenters stereoselectively, which is characterized by directly constructing two C-C bonds from four C(sp 3 )-H bonds. This new method features mild conditions, broad substrate scope, and excellent functional group compatibility.

Three pairs of chiral Ln-Ag(I) clusters d/l-Ln 3 Ag 5 with C 3 symmetry were prepared by d/l-penicillamine as multidentate ligand bridged Ln 3+ and Ag(I) ions. The chiral ligand induced the molecular cluster to be chiral, and the CD spectra of the chiral compounds d/l-Ln 3 Ag 5 were slightly blue-shifted due to the lanthanide contraction. The studies of optical properties indicated that tunable photoluminescence from {AgS}-to-Ln 3+ was achieved by introducing Ln 3+ ions with different emission bands or regulating various excitation light.

A family of nanoclusters, [Ln 33 (EDTA) 12 (OAc) 2 (CO 3 ) 4 (μ 3 -OH) 36 (μ 5 -OH) 4 (H 2 O) 38 ]·OAc· x H 2 O ( x ≈ 50, Ln = Sm for 1 ; x ≈ 70, Ln = Eu for 2 ) and [Gd 32 (EDTA) 12 (OAc) 2 (C 2 O 4 )(CO 3 ) 2 (μ 3 -OH) 36 (μ 5 -OH) 4 (H 2 O) 36 ]· x (H 2 O) ( x ≈ 70 for 3 ; H 4 EDTA = ethylene diamine tetraacetic acid), was prepared through the assembly of repeating subunits under the action of an anion template. The analysis of the structures showed that compounds 1 and 2 containing 33 Ln 3+ ions were isostructural, which were constructed by three kinds of subunits in the presence of CO 3 2- as an anion template, while compound 3 had a slightly different structure. Compound 3 containing 32 Gd 3+ ions was formed by three types of subunits in the presence of CO 3 2- and C 2 O 4 2- as a mixed anion template. The CO 3 2- anions came from the slow fixation of CO 2 in the air. Meanwhile, one kind of high-nuclearity lanthanide clusters showed high chemical stability. The quantum Monte Carlo (QMC) calculation suggested that weak antiferromagnetic interactions were dominant between Gd 3+ ions in 3 . Magnetocaloric studies showed that compound 3 had a large entropy change of 43.0 J kg -1 K -1 at 2 K and 7 T. Surprisingly, compound 2 showed excellent recognition and detection effects for permanganate in aqueous solvents based on the fluorescence quenching phenomenon.

An efficient implementation of the quadratic unitary coupled-cluster singles and doubles (qUCCSD) scheme for calculations of electronic ground and excited states using an unrestricted molecular spin-orbital formulation and an efficient tensor contraction library is reported. The accuracy of the qUCCSD scheme and the efficiency of the present implementation are demonstrated using extensive benchmark calculations of excitation energies and an application to S 0 → S 1 vertical excitation energies for cis - and trans -4 a ,4 b- dihydrotriphenylene. The qUCCSD scheme has been shown to provide improved excitation energies compared with the UCC3 scheme formulated based on perturbation theory. A UCC truncation scheme that can provide excitation energies correct through the fourth order is also presented to further improve the accuracy of the qUCCSD scheme.

Multiphoton excitation promises opportunities for opening new photochemical reaction pathways and controlling photoproduct distributions. We demonstrate photonic control of the 6π photocyclization of ortho -terphenyl to make 4 a ,4 b -dihydrotriphenylene (DHT). Using pump-repump-probe spectroscopy we show that 1 + 1' excitation to a high-lying reactant electronic state generates a metastable species characterized by a red absorption feature that accompanies a repump-induced depletion in the one-photon trans -dihydro product ( trans -DHT); signatures of the new photoproduct are clearer for a structural analogue of the reactant that is sterically inhibited against one-photon cyclization. Quantum-chemical computations support assignment of this species to cis -DHT, which is accessible photochemically along a disrotatory coordinate from high-lying electronic states reached by 1 + 1' excitation. We use time-resolved spectroscopy to track photochemical dynamics producing cis -DHT. In total, we demonstrate that selective multiphoton excitation opens a new photoreaction channel in these photocyclizing reactants by taking advantage of state-dependent correlations between reactant and product electronic states.

The synergetic combination of anion photoelectron spectroscopy and high-level relativistic coupled-cluster calculations was employed to study the anion, HThO - . The atomic connectivity of this anion was found to be HThO - and not ThOH - . Vibrational and electronic energy spacings in the HThO - photoelectron spectrum were measured and calculated, with good agreement between them being found. Computations yielded electronic energies and equilibrium structures as well as enabling orbital analyses. The adiabatic electron affinity (EA a ) of HThO was determined to be 1.297 ± 0.035 eV.

A combined anion photoelectron spectroscopic and relativistic coupled-cluster computational study of the electronic structure of the UN 2 molecule is presented. Because the photoelectron spectrum of the uranium dinitride negative ion, UN 2 - , directly reflects the electronic structure of neutral UN 2 , we have measured and relied upon the photoelectron spectrum of the UN 2 - anion as a means of mapping the electronic structure of neutral UN 2 . In addition to the electron affinity of the UN 2 ground state, energy levels of the UN 2 excited states were well characterized by the close interplay between the experiment and high-level theory. We found that both electron attachment and electronic excitation significantly bend the UN 2 molecule and elongate its U≡N bond. Implications for the activation of UN 2 are discussed.

Benchmark scalar-relativistic delta-coupled-cluster calculations of hetero-site double core ionization energies of small molecules containing second-row elements are reported. The present study has focused on the high-spin triplet components of two-site double core-ionized states, which are single reference in character and consistent with the use of standard coupled-cluster methods. Contributions to computed double core ionization energies from electron-correlation and basis-set effects as well as corrections to the core-valence separation approximation have been analyzed. On the basis of systematic convergence of computational results with respect to these effects, delta-coupled-cluster calculations have been shown to be capable of providing accurate double core ionization energies with remaining errors estimated to be below 0.3 eV, and thus they are recommended for use to facilitate experimental studies of two-site double core-ionized states that are involved in X-ray pump/X-ray probe studies of electronic and molecular dynamics following inner shell ionization or excitation.

Medium resolution (Δν̃ ∼ 3 GHz) laser-induced fluorescence (LIF) excitation spectra of a rotationally cold sample of YbOH in the 17300-17950 cm -1 range have been recorded using two-dimensional (excitation and dispersed fluorescence) spectroscopy. High resolution (Δλ ∼ 0.65 nm) dispersed laser-induced fluorescence (DLIF) spectra and radiative decay curves of numerous bands detected in the medium resolution LIF excitation spectra were recorded. The vibronic energy levels of the X̃ 2 Σ + state were predicted using a discrete variable representation approach and compared with observations. The radiative decay curves were analyzed to produce fluorescence lifetimes. DLIF spectra resulting from high resolution (Δν̃ < 10 MHz) LIF excitation of individual low-rotational lines in the  Ã 2 Π 1/2 (0,0,0)-X̃ 2 Σ + (0,0,0), Ã 2 Π 1/2 (1,0,0)-X̃ 2 Σ + (0,0,0), and [17.73]Ω = 0.5(0,0,0)-X̃ 2 Σ + (0,0,0) bands were also recorded. The DLIF spectra were analyzed to determine branching ratios which were combined with radiative lifetimes to obtain transition dipole moments. The implications for laser cooling and trapping of YbOH are discussed.

Experimentally and theoretically determined magnetic and electric dipole moments, bond distances, and vibrational spacings are used for a comparative study of the bonding in ThF and ThCl. Numerous bands in the visible electronic spectra between 16 400 and 18 800 cm -1 of supersonically cooled molecular beam samples have been detected using medium-resolution (Δν ≈ 0.1 cm -1 ) 2D spectroscopy. High-resolution (Δν < 20 MHz) field-free, Stark, and Zeeman spectroscopy of the detected [18.6]Ω = 3/2 - X 2 Δ 3/2 band of ThF near 538.4 nm and the [18.2]Ω = 3/2 - X 2 Δ 3/2 band of ThCl near 551.0 nm have been recorded and analyzed. Stark shifts and splitting were analyzed to produce | μ⃗ el | values of 1.453(7) D and 0.588(9) D for the X 2 Δ 3/2 and [18.6]Ω = 3/2 states of ThF, respectively, and 2.022(35) D and 3.020(55) D for the X 2 Δ 3/2 and [18.2]Ω = 3/2 states of ThCl. Zeeman splittings and shifts were analyzed to produce g e values of 1.038(4) and 1.079(4) for the X 2 Δ 3/2 and [18.6]Ω = 3/2 states of ThF and 1.130(4) and 1.638(4) for the X 2 Δ 3/2 and [18.2]Ω = 3/2 states of ThCl. Analysis of g e values demonstrates that the X 2 Δ 3/2 and [18.6]Ω = 3/2 states of ThF and the X 2 Δ 3/2 state of ThCl are predominately 2 Δ 3/2 spin-orbit components, whereas the [18.2]Ω = 3/2 state of ThCl is an admixture of 2 Δ 3/2 and 2 Π 3/2 spin-orbit components. A molecular orbital description of the ground states is used to rationalize the observed | μ⃗ el |values for the ThX (X = F, Cl, O, and S) series and garner insight into the bonding mechanism. The dipole moments in the ground state of ThF and ThCl have been calculated using relativistic coupled-cluster methods. It is demonstrated that the systematic inclusion of electron-correlation contributions plays an essential role in obtaining accurate predictions for the dipole-moment values in ThF and ThCl.

A joint experimental-computational study of the molecular structure and vibrational spectra of the XeF 6 molecule is reported. The vibrational frequencies, intensities, and in particular the isotopic frequency shifts of the vibrational spectra for 129 XeF 6 and 136 XeF 6 isotopologues recorded in the neon matrix agree very well with those obtained from relativistic coupled-cluster calculations for XeF 6 in the C 3v structure, thereby strongly supporting the observation of the C 3v conformer of the XeF 6 molecule in the neon matrix. A C 3v transition state connecting the C 3v and O h local minima is located computationally. The calculated barrier of 220 cm -1 between the C 3v minima and the transition state corroborates the experimental observation of the C 3v conformer and the absence of the O h conformer in solid noble gas matrices. For comparison matrix-isolation spectra have also been recorded and analyzed for the 129 XeOF 4 and the 136 XeOF 4 isotopologues. The matrix-isolation complexation shifts obtained for the XeF 6 ·NCCH 3 relative to those of free matrix isolated XeF 6 and CH 3 CN are in good agreement with those reported for crystalline XeF 6 ·NCCH 3 .

Benchmark scalar-relativistic coupled-cluster calculations for dissociation energies of the 20 diatomic molecules containing 3d transition metals in the 3dMLBE20 database ( J. Chem. Theory Comput. 2015 , 11 , 2036 ) are reported. Electron correlation and basis set effects are systematically studied. The agreement between theory and experiment is in general satisfactory. For a subset of 16 molecules, the standard deviation between computational and experimental values is 9 kJ/mol with the maximum deviation being 15 kJ/mol. The discrepancies between theory and experiment remain substantial (more than 20 kJ/mol) for VH, CrH, CoH, and FeH. To explore the source of the latter discrepancies, the analysis used to determine the experimental dissociation energies for VH and CrH is revisited. It is shown that, if improved values are used for the heterolytic C-H dissociation energies of di- and trimethylamine involved in the experimental determination, the experimental values for the dissociation energies of VH and CrH are increased by 18 kJ/mol, such that D 0 (VH) = 223 ± 7 kJ/mol and D 0 (CrH) = 204 ± 7 kJ/mol (or D e (VH) = 233 ± 7 kJ/mol and D e (CrH) = 214 ± 7 kJ/mol). The new experimental values agree quite well with the calculated values, showing the consistency of the computation and the measured reaction thresholds.

The peroxyiodomethyl radical, CH2IOO, was generated in cryogenic matrices using tandem supersonic nozzles. One hyperthermal nozzle decomposes diiodomethane (CH2I2) to generate intense beams of CH2I radicals, while the second nozzle continuously deposits O2/argon (Ar) on the matrix at 10 K. The CH2I and O2 in the Ar matrix react to produce the target peroxy radical (CH2IOO). The absorption spectra of the products are monitored with a Fourier transform infrared spectrometer. Eight of the 12 fundamental infrared bands for CH2IOO were observed in an argon matrix at 5 K. The experimental frequencies (cm(-1)) are ν3 = 1407.3, ν4 = 1230.4, ν5 = 1223.2, ν6 = 1085.3, ν7 = 919.9, ν8 = 839.9, ν9 = 567.5, and ν10 = 496.2. Additional confirmation for the vibrational assignment comes from a study of the CH2I(18)O(18)O isotopic species. The six observed frequencies (cm(-1)) for CH2I(18)O(18)O are ν3 = 1407.8, ν4 = 1228.0, ν6 = 1030.8, ν7 = 899.6, ν8 = 836.0, and ν10 = 494.6. Unlike CH2I(16)O(16)O, the ν5 and ν9 bands were not observed for CH2I(18)O(18)O. To guide the experimental analysis, ab initio calculations of the infrared spectrum based on second-order vibrational perturbation theory were performed using force fields computed with relativistic coupled-cluster methods. The experimental frequencies are shown to be in good agreement with the computed fundamental frequencies except for ν9 (for CH2IOO) and ν10 (for CH2I(18)O(18)O). Our findings were compared with the study by Lee and Lee conducted in a para-H2 matrix. The fundamental frequencies are in good agreement (within 6 cm(-1)) except for the two low-frequency modes, ν9 (for CH2IOO) and ν10 (for CH2I(18)O(18)O) likely due to different matrix shifts for para-H2 and Ar matrices. In addition, our calculations are in somewhat better agreement with the experiment values than the calculations by Lee and Lee. Our study also shows that reaction CH2I + O2 produces the peroxy radical CH2IOO in cold matrices (10 K) instead of Criegee intermediate CH2OO, which is generated in gas phase (300 K and low pressure); the same finding was also reported by Lee and Lee.

The (6,0)[16.0]1.5-X(2)Δ(5/2) and (7,0)[16.0]3.5-X(2)Δ(5/2) bands of IrSi have been recorded using high-resolution laser-induced fluorescence spectroscopy. The field-free spectra of the (191)IrSi and (193)IrSi isotopologues were modeled to generate a set of fine, magnetic hyperfine, and nuclear quadrupole hyperfine parameters for the X(2)Δ(5/2)(v = 0), [16.0]1.5(v = 6), and [16.0]3.5 (v = 7) states. The observed optical Stark shifts for the (193)IrSi and (191)IrSi isotopologues were analyzed to produce the permanent electric dipole moments, μ(el), of -0.414(6) D and 0.782(6) D for the X(2)Δ(5/2) and [16.0]1.5 (v = 6) states, respectively. Properties of the X(2)Δ(5/2) state computed using relativistic coupled-cluster methods clearly indicate that electron correlation plays an essential role. Specifically, inclusion of correlation changes the sign of the dipole moment and is essential for achieving good accuracy for the nuclear quadrupole coupling parameter eQq0.

Electrochemical oxidation of pentaaryl 2 containing two furan moieties occurs sequentially to give diketone 8 after two-electron transfer. Further oxidation with another two-electron transfer gives the corresponding tetraketone 9. Radical cation intermediate is detected by absorption spectroscopy. The radical intermediates of different regiochemistry have been shown to exhibit different oxidation potentials as revealed by the differential pulse voltammetry.

The reaction of beta-lactam carbenes with aryl isonitriles proceeded in a novel [2 + 2] fashion to give high yields of 2-azetidinonylidene indoles 4, which underwent an unprecedented rearrangement to furnish 4-arylimino-delta-carbolin-2-ones 5 in almost quantitative yields. Acid catalyzed rearrangement and the subsequent hydrolysis of 2-azetidinonylidene indoles 4 produced two types of delta-carbolin-2,4-diones 10 and 11, respectively, in good to excellent yields. The photophysical study showed that both delta-carbolin-2,4-diones 10 and 11 are highly fluorescent with the fluorescent quantum yields being up to 0.43.

The nucleophilic addition of beta-lactam-4-ylidenes 2, a type of ambiphilic cyclic amidocarbene, to aryl isocyanates has been studied and their application in organic synthesis has been demonstrated. Thermolysis of spiro[beta-lactam-4,2'-oxadiazolines] 1 in the presence of aryl isocyanates afforded both N-lactam and O-lactam substituted spiro[azetidine-2-one-4,3'-indole-2'-one] derivatives 5 and 6 in the total yield of 65-86%. Upon hydrolysis, products 5 and 6 were converted into spiro[azetidine-2-one-4,3'-indole-2'-one] 9 that was analogous to known biologically active compounds.

[structure: see text] Furan-containing oligoaryl cyclophanene 1 and the corresponding cyclophane 2 were synthesized from propargylic dithioacetal 3. The electrochemical and photophysical properties and the fluxional behavior of these molecules have been examined. The emission of 1 appeared at 499 nm whereas that of 2 appeared at 389 nm.