Changes in the state of charge of a high-area RuOx electrode in an operating RuOx|Nafion|IrOx supercapacitor were monitored in situ by time-resolved, transmission Ru K-edge X-ray absorption spectroscopy (XAS). Linear and reversible variations in the intensity of the transmitted X-ray beam as a function of time were found by fixing the energy of the incident X-ray beam, Ei, at judiciously selected values within the Ru K-edge X-ray near edge structure (XANES), while the supercapacitor was charged and discharged at constant current. The sign of the slope of these temporal signals was found to vary, depending on the value of Ei. This behavior could be rationalized based on the spectral differences between the Ru K-edge XANES of RuOx in the fully oxidized and fully reduced states, recorded in situ from films of the material electrodeposited on a gold substrate in the fluorescence mode.This paper is dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday for his outstanding contributions to electrochemistry 相似文献
Ozonization reaction of simple alkenes was studied by means of FT infrared absorption gas spectroscopy. The reaction was performed
at 95 K in neat films of the reactants. IR absorption spectra of the gaseous products were recorded. The spectra were analyzed
combining experimental results with theoretical calculations performed at B3LYP 6-311++G (3df, 3pd) level. We found that among
all theoretically predicted conformers of propene secondary ozonide, only one which has the O-O half-chair configuration for
the five membered ring and the radical attached in the equatorial position was present in the sample. Samples of 1-butene and 1-heptene secondary ozonides consist from two conformers of very
similar energy (ΔH=0.3 kJ/mol). The most stable conformer for both ozonides is the one with O-O half-chair configuration of the five membered
ring and the radical attached in equatorial position and the aliphatic chain in gauche position. The second stable conformer has the aliphatic chain in anti position. 相似文献
The photodissociation of pyruvic acid at 193 nm has been studied and one of the photoproducts, methane, was detected using
an infrared diode laser absorption probe technique. Using second-derivative absorption spectroscopy at 1346.326 cm-1[R(-)(7) transition in v4 band], the progress of the reaction was monitored. The quantum yield of formation of methane = 0.09 ± 0.01 and was further
corroborated by a simple measurement of pressure changes following the photolysis. The secondary photolysis of the photoproduct
acetaldehyde via the established route was found to be negligible. This result may help to account for the energetics of the
photodissociation process by a 6.4 eV excimer laser photon. The possibility of using this technique to examine the nascent
methane molecule in real-time domain to gain better insight of the dissociation dynamics is also indicated. 相似文献
To test the molecular exciton theory for heterodimeric chromophores, various heterodimers and clusters, in which two different dyes were stacked alternately, were prepared by hybridizing two oligodeoxyribonucleotides (ODNs), each of which tethered a different dye on D ‐threoninol at the center of the strand. NMR analyses revealed that two different dyes from each strand were stacked antiparallel to each other in the duplex, and were located adjacent to the 5′‐side of a natural nucleobase. The spectroscopic behavior of these heterodimers was systematically examined as a function of the difference in the wavelength of the dye absorption maxima (Δλmax). We found that the absorption spectrum of the heterodimer was significantly different from that of the simple sum of each monomeric dye in the single strand. When azobenzene and Methyl Red, which have λmax at 336 and 480 nm, respectively, in the single strand (Δλmax=144 nm), were assembled on ODNs, the band derived from azobenzene exhibited a small hyperchromism, whereas the band from Methyl Red showed hypochromism and both bands shifted to a longer wavelength (bathochromism). These hyper‐ and hypochromisms were further enhanced in a heterodimer derived from 4′‐methylthioazobenzene and Methyl Red, which had a much smaller Δλmax (82 nm; λmax=398 and 480 nm in the single‐strand, respectively). With a combination of 4′‐dimethylamino‐2‐nitroazobenzene and Methyl Red, which had an even smaller Δλmax (33 nm), a single sharp absorption band that was apparently different from the sum of the single‐stranded spectra was observed. These changes in the intensity of the absorption band could be explained by the molecular exciton theory, which has been mainly applied to the spectral behavior of H‐ and/or J‐aggregates composed of homo dyes. However, the bathochromic band shifts observed at shorter wavelengths did not agree with the hypsochromism predicted by the theory. Thus, these data experimentally verify the molecular exciton theory of heterodimerization. This coherent coupling among the heterodimers could also partly explain the bathochromicity and hypochromicity that were observed when the dyes were intercalated into the duplex. 相似文献
Following on from a previous work (Punter et al., IJQC 2019, 119, 23), pseudopotential sets are developed and tested for a variety of sp2 and sp3 carbon fragments. These fragments contain only one or two explicit protons and electrons, and make use of non-atom-centered potentials. They are tested with density functional theory calculations in a selection of chemical environments in which several physical characteristics, including orbital and first ionization energies, are found to be well reproduced. They are then employed in the reproduction of molecular absorption spectra for large organic molecules and carbon allotropes, and are found to recreate both absorption and electronic circular dichroism spectra to a high accuracy. They are also found significantly to increase the computational efficiency of time dependent density functional theory (TDDFT) calculations in which they are used. 相似文献
The synthesis of organometallic complexes of modified 26π-conjugated hexaphyrins with absorption and emission capabilities in the third near-infrared region (NIR-III) is described. Symmetry alteration of the frontier molecular orbitals (MOs) of bis-PdII and bis-PtII complexes of hexaphyrin via N-confusion modification led to substantial metal dπ–pπ interactions. This MO mixing, in turn, resulted in a significantly narrower HOMO–LUMO energy gap. A remarkable long-wavelength shift of the lowest S0→S1 absorption beyond 1700 nm was achieved with the bis-PtII complex, t -Pt2-3 . The emergence of photoacoustic (PA) signals maximized at 1700 nm makes t -Pt2-3 potentially useful as a NIR-III PA contrast agent. The rigid bis-PdII complexes, t -Pd2-3 and c -Pd2-3 , are rare examples of NIR emitters beyond 1500 nm. The current study provides new insight into the design of stable, expanded porphyrinic dyes possessing NIR-III-emissive and photoacoustic-response capabilities. 相似文献
β‐Carotene in n‐hexane was examined by femtosecond transient absorption and stimulated Raman spectroscopy. Electronic change is separated from vibrational relaxation with the help of band integrals. Overlaid on the decay of S1 excited‐state absorption, a picosecond process is found that is absent when the C9‐methyl group is replaced by ethyl or isopropyl. It is attributed to reorganization on the S1 potential energy surface, involving dihedral angles between C6 and C9. In Raman studies, electronic states S2 or S1 were selected through resonance conditions. We observe a broad vibrational band at 1770 cm?1 in S2 already. With 200 fs it decays and transforms into the well‐known S1 Raman line for an asymmetric C=C stretching mode. Low‐frequency activity (<800 cm?1) in S2 and S1 is also seen. A dependence of solvent lines on solute dynamics implies intermolecular coupling between β‐carotene and nearby n‐hexane molecules. 相似文献
Ultrafast optical control of intramolecular charge flow was demonstrated, which paves the way for photocurrent modulation and switching with a highly wavelength-selective ON/OFF ratio. The system that was explored is a fac-[Re(CO)3(TTF-DPPZ)Cl] complex, where TTF-DPPZ=4’,5’-bis(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2’,3’-c]phenazine. DFT calculations and AC-Stark spectroscopy confirmed the presence of two distinct optically active charge-transfer processes, namely a metal-to-ligand charge transfer (MLCT) and an intra-ligand charge transfer (ILCT). Ultrafast transient absorption measurements showed that the ILCT state decays in the ps regime. Upon excitation to the MLCT state, only a long-lived 3MLCT state was observed after 80 ps. Remarkably, however, the bleaching of the ILCT absorption band remained as a result of the effective inhibition of the HOMO–LUMO transition. 相似文献
A series of chlorin-bacteriochlorin dyads (derived from naturally occurring chlorophyll-a and bacteriochlorophyll-a), covalently connected either through the meso-aryl or β-pyrrole position (position-3) via an ester linkage have been synthesized and characterized as a new class of far-red emitting fluorescence resonance energy transfer (FRET) imaging, and heavy atom-lacking singlet oxygen-producing agents. From systematic absorption, fluorescence, electrochemical, and computational studies, the role of chlorin as an energy donor and bacteriochlorin as an energy acceptor in these wide-band-capturing dyads was established. Efficiency of FRET evaluated from spectral overlap was found to be 95 and 98 % for the meso-linked and β-pyrrole-linked dyads, respectively. Furthermore, evidence for the occurrence of FRET from singlet-excited chlorin to bacteriochlorin was secured from studies involving femtosecond transient absorption studies in toluene. The measured FRET rate constants, kFRET, were in the order of 1011 s−1, suggesting the occurrence of ultrafast energy transfer in these dyads. Nanosecond transient absorption studies confirmed relaxation of the energy transfer product, 1BChl*, to its triplet state, 3Bchl*. The 3Bchl* thus generated was capable of producing singlet oxygen with quantum yields comparable to their monomeric entities. The occurrence of efficient FRET emitting in the far-red region and the ability to produce singlet oxygen make the present series of dyads useful for photonic, imaging and therapy applications. 相似文献
Structures of Pd/zeolites immersed in solvents were measured by in situ X‐ray absorption fine structure (XAFS). Systematic studies revealed that the selection of an appropriate support (USY‐zeolite), thermal treatment temperature of USY, solvent (o‐xylene), H2 partial pressure (6 %), and the use of a Pd amine complex affect the structure of Pd. As a result, we found that monomeric Pd can be obtained in the USY support with H2 bubbling in o‐xylene. The structural properties of Pd correlate well with its catalytic performance in the Suzuki–Miyaura coupling reactions; a very high TON of up to 11 000 000 was obtained over the monomeric Pd.相似文献
A hexanuclear gold(I) selenido cluster and its sulfido counterpart, [Au6{μ‐Ph2PN(CH2‐o‐Py)PPh2}3(μ3‐E)2](ClO4)2 (E = S, Se), with bridging bis(diphenylphosphino)amine ligands were synthesized and characterized. The X‐ray crystal structure of the selenido cluster was determined, with the gold core possessing a distorted heterocubane structure. Intramolecular aurophilic interactions with short Au(I)?Au(I) contacts of around 3.09–3.13 Å were observed. The complexes were found to emit strongly in the solid state with orange to red emission colors. Their electronic absorption and emission properties were also investigated. 相似文献
The complexation of 1-[(4-benzothiazolyl)phenyl]-4,7,10,13-tetraoxa-1-aza-cyclopenta-decane with Ba2+ and Ca2+ cations was investigated spectrophotometrically and spectrofluorometrically. The stability constants of the complexes formed are: for Ba2+ logKst=3.17±0.01 (absorption) and logKst=2.95±0.03 (fluorescence); for Ca2+ logKst=3.71±0.02 (absorption) and logKst=3.58±0.05 (fluorescence). Protonation of the ligand leads to fluorescence quenching. AM1 and PPP quantum chemical calculations were used to predict molecular geometry, proton affinities and the spectra of the compounds studied.Dedicated to Prof. Dr. Karl-Heinz Drexhage on the occasion of his 60th birthday 相似文献
采用全电子相对论密度泛函理论探索多种六聚吡咯大环锕酰基配合物(nAn;n=1~3;An=U,Np and Pu)的电子结构本质、成键规律和化学反应特性。结构优化发现大环配体空穴大小与锕酰离子尺寸相当时,配合物锕酰基采用性对规则的六角双锥结构,而当空穴尺寸相对大时,配合物则采取扭曲结构以降低体系能量。当配体相同时,随着铀、镎、钚变化,An=O伸缩振动频率逐渐变小,这与优化的键长和键级变化规律相一致。QTAIM(quantum theory of atoms in molecule)拓扑分析显示An-N为弱共价单键特征,具有较大离子性成分。依据不同铀源,得到与大环配体的反应自由能均小于146 kJ·mol~(-1),与实验合成配合物的反应能计算数值相当。对含铀配合物电子吸收光谱计算显示,低能(近红外和可见光区)的吸收带具有全部或较大的配体→金属电荷转移性质贡献。 相似文献
As highly reactive acylphosphine oxide‐based photoinitiators (PIs) are limited in the application for dental materials by their absorption behavior, we were interested to prepare acylgermane 1 . UV‐Vis absorption maximum of the important n–π* transition was red shifted about 30 nm compared to monoacylphosphine oxides. Photo‐DSC results with a dental LED lamp showed nearly the same reactivity for 1 compared to camphorquinone (CQ), while monoacylphosphine oxides are not reactive. In broadband irradiation experiments, significantly higher reactivity compared to CQ was found. Application‐oriented tests showed sufficient storage stability of the formulation and excellent photobleaching behavior.
New fulgides of the indole series with adamantylidene fragments were synthesized: 3-(adamant-2-ylidene)-2-[1-(3-indolylethylidene)]succinic anhydride (I) and 3-(adamant-2-ylidene)-2-(3-indolylmethylene)]succinic anhydride (2). By means of electronic absorption and1H NMR spectroscopy and X-ray diffraction analysis, fulgides1 and2 were shown to haveZ- andE-configurations, respectively. The photochemical properties of1 and2 were studied. It was shown that along withZ-E photoisomerization of these compounds, in solution they undergo a cyclization reaction to yield a colored photoproduct. Specific structural features of fulgide1 affecting its photochemical properties were discussed. The introduction of a bulky adamantylidene group decreases the extent of the conversion of compound1 into cyclic isomerC.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2301–2305, September, 1996. 相似文献
The magnetic properties of LnIII and AnIII complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single-crystal X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal–ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher-order terms of the dipolar and contact contributions are required, especially for the lightest LnIII and almost all the studied AnIII. Bleaney's parameters <Sz>a and relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of <Sz>a and . However, the values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for LnIII. Other parameters, such as the crystal field parameter and the hyperfine constants Fi obtained from the experimental data of the [An(ethyl-dpa)3]3− complexes (ethyl-dpa=4-ethyl-2,6-dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory. 相似文献