8-羟基喹啉的丙烯酸酯及其聚合物的荧光光谱研究

在同一分子中既含有电子给体基团,又含有电子受体基团的单体,如甲基丙烯酸二甲氨基苄酯(DMABMA),N-(4-N′,N′-二甲氨基苯基)代丙烯酰胺(DMAPAA)及其聚合物的荧光光谱颇为有趣。     

Experimental and theoretical study on generalized oscillator strengths of the valence-shell electronic excitations in CF4

We report an angle-resolved electron energy loss spectroscopy (EELS) study on the valence-shell electronic excitations in CF(4). Experimentally momentum-transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles for low-lying electronic excitations at 12.6, 13.8, and 14.8 eV are derived from EELS spectra measured at an incident electron energy of 3 keV. We also calculate GOS profiles using theoretical wave functions at the equation-of-motion coupled cluster singles and doubles level. There are good agreements between experiment and theory except for a significant discrepancy at small momentum transfer for the 1t(l) → 3s Rydberg excitation at 12.6 eV. The experimental GOS profile for 1t(l) → 3s exhibits a shape that is typical of a dipole allowed transition, while the excitation is formally dipole forbidden. This symmetry breaking behavior is rationally accounted for by qualitatively analyzing the nature of vibronic coupling effects. For the excitation band at 13.8 eV, a shoulder and extrema are observed in the GOS profile and are then found to be mainly due to the 2(1)T(2) transition. Furthermore, the theoretical GOS profile for the 2(1)T(2) transition exhibits a remarkable oscillatory pattern; its origin is discussed by considering multicenter interference effects. For the 14.8 eV excitation band, the predominant nondipole nature of the underlying transitions are revealed and comparisons with the theoretical calculations show that major contributions to this band come from the 4t(2) → 3p excitation.     

Inner shell excitation spectroscopy of biphenyl and substituted biphenyls: probing ring-ring delocalization

Quantitative optical oscillator strength spectra for C 1s excitation and ionization of gas-phase biphenyl, decafluorobiphenyl, and 2,2'-bis(bromomethyl)-1,1'-biphenyl have been derived from electron energy loss spectroscopy recorded under electric dipole dominated conditions. The C 1s X-ray absorption spectrum of hexaphenylbenzene has been recorded in the solid state. The C 1s spectral features are interpreted with the aid of ab initio calculations for core excitation of benzene, biphenyl, hexafluorobenzene, and decafluorobiphenyl. A weak feature at 287.7 eV in biphenyl is identified as a C 1s --> pi(deloc) transition, characteristic of ring-ring delocalization. Its intensity and position are shown to be related to the average torsion angle and thus the extent of pi-pi-interaction between adjacent aromatic rings. The effects of perfluoro substitution on core excitation spectra are also characterized and discussed.     

Inner-shell excitation spectroscopy and X-ray photoemission electron microscopy of adhesion promoters

The C 1s, Si 2p, Si 2s, and O 1s inner-shell excitation spectra of vinyltriethoxysilane, trimethylethoxysilane, and vinyltriacetoxysilane have been recorded by electron energy loss spectroscopy under scattering conditions dominated by electric dipole transitions. The spectra are converted to absolute optical oscillator strength scales and interpreted with the aid of ab initio calculations of the inner-shell excitation spectra of model compounds. Electron energy loss spectra recorded in a transmission electron microscope on partly cured adhesion promoter, atomic force micrographs, and images and X-ray absorption spectra from X-ray photoemission electron microscopy of as-spun and cured vinyltriacetoxysilane-based adhesion promoter films on silicon are presented. The use of these measurements in assisting chemistry studies of adhesion promoters for electronics applications is discussed.     

Deconvolution of lignin fluorescence spectra: A contribution to the comparative structural studies of lignins

In this work, we deconvoluted the fluorescence spectra of lignin and a lignin model compound using a combination of one symmetric (Gaussian) and the most appropriate number of asymmetric (Log-normal) models. We aimed to obtain new data on the structural characteristics of lignin as a complex molecule using fluorescence spectroscopy in combination with FTIR spectra. We analyzed the emission spectra of the lignin model compound, DHP, and isolated lignins from a deciduous tree, poplar, and a coniferous tree, spruce. The number of applied asymmetric components was varied for each sample until the component positions obtained from deconvolution of a series of spectra became constant. The lignin model compound contains fewer components in the emission spectrum. The same components in the spectra of all three samples show that they contain the same fluorophores. The small shift of the peak position can be attributed to the influence of different environments. The FTIR spectra of the three polymers show a small difference between their structures. The main difference among the IR spectra of the three samples is in the intensity of some peaks. The text was submitted by the authors in English.     

Deconvolution of fluorescence spectra: contribution to the structural analysis of complex molecules

Fluorescence spectroscopy is a sensitive analytical tool in the studies of both simple and complex molecular structures. In complex molecules, however, determining the number and position of components may give a specific insight into the structure, complementary to the other analytical techniques. We applied log–normal model to analyze fluorescence of simple monofluorophore molecule. In order to analyze spectra where both fluorophores and Raman emission bands were present, we developed a method obtained by combination of the symmetric, Gaussian, for Raman and asymmetric, log–normal model, for fluorescence, applicable to the molecules of different complexity. Technically, for each sample we varied excitation wavelength with 5 nm step and recorded the corresponding emission spectra. They were subsequently used for component analysis. Position of each component was plotted against the excitation wavelength. Applying this approach we could identify minimal number of components having stable positions, while their approximate probability density (APD) in a spectral series was correlated with the probable number of fluorophores in the molecule. The method was tested on molecules containing different number of fluorophores: monomers involved in the synthesis of plant polymer lignin—coniferyl alcohol (one fluorophore), ferulic acid (two fluorophores) and on lignin model compound produced from these monomers (many fluorophores). All investigated species belong to benzene-substituted class of compounds, and it is reasonable to assume that they have similar fluorescence band contour. We also report the results of environmental scanning electron microscopy (ESEM) studies showing multilayered dehydrogenative polymer (DHP) structure, in order to show complexity of the polymer. Our results present complementarity of these two approaches in the structural studies of the lignin model compound.     

Dielectric barrier discharge non-thermal micro-plasma for the excitation and emission spectrometric detection of ammonia

Dielectric-barrier discharge (DBD) in argon as a cold source is used for the excitation of gaseous inorganic small molecules at atmospheric pressure. By choosing ammonia as a model molecule, the excitation process and the characteristics of the emission spectra are investigated. The emission spectra are recorded by designing either an open-end or an enclosed DBD excitation/emission source. The enclosed excitation mode effectively eliminates the background emissions arising from the ambient air components, especially those from nitrogen. Two emission lines attributed to the excitation of ammonia, i.e., 326.2 and 336.5 nm, are clearly isolated from the background emission spectra of argon, providing the basis for quantitative analysis. A detection limit of 0.37 ppm is achieved within a linear range of 1.2-35 ppm by monitoring at 326.2 nm. In practice, gaseous samples containing ammonia collected in a public toilet are excited in an enclosed excitation source and the emission at 326.2 nm is monitored for quantitative analysis. An ammonia concentration of 2.4 ppm is derived in the original atmospheric sample, and a spiking recovery of 94.7% is achieved at a 10 ppm ammonia level. This study shows that DBD cold excitation in combination with optical emission spectrometry (OES) offers a promising approach for the detection of ammonia pollution.     

Photolysis of bisphenol‐based polyurethanes in solution

Photolysis of bisphenol‐based polyurethanes, using bisphenols A, S, and AF with methylene diphenyl diisocyanate (MDI), has been shown by the observed changes in fluorescence spectra, reduced viscosity, and UV absorbance. Analysis of the fluorescence spectra of model compounds and polymers showed that para‐photo‐Fries and cleavage‐type products were the major components formed during photolysis. The reduced viscosity and UV absorbance changes are consistent with a two‐step photodegradation process. The reduced viscosity changes indicate that oxygen inhibition on the cleavage process is more significant for bisphenol S‐based polyurethanes than for bisphenol A‐ and bisphenol AF‐based polyurethanes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1331–1339, 1999     

Optical gap measurements on individual boron nitride nanotubes by electron energy loss spectroscopy.

Electromagnetic response of individual boron nitride nanotubes (BNNTs) has been studied by spatially resolved electron energy loss spectroscopy (EELS). We demonstrate how dedicated EELS methods using subnanometer electron probes permit the analysis of local dielectric properties of a material on a nanometer scale. The continuum dielectric model has been used to analyze the low-loss EEL spectra recorded from these tubes. Using this model, we demonstrate the weak influence of the out-of-plane contribution to the dielectric response of BNNTs. The optical gap, which can be deduced from the measurements, is found to be equal to 5.8 +/- 0.2 eV, which is close to that of the hexagonal boron nitride. This value is found to be independent of the nanotubes configuration (diameter, helicity, number of walls, and interaction between the different walls).     

A UV resonance Raman (UVRR) spectroscopic study on the extractable compounds of Scots pine (Pinus sylvestris) wood. Part I: lipophilic compounds

The wood resin in Scots pine (Pinus sylvestris) stemwood and branch wood were studied using UV resonance Raman (UVRR) spectroscopy. UVRR spectra of the sapwood and heartwood hexane extracts, solid wood samples and model compounds (six resin acids, three fatty acids, a fatty acid ester, sitosterol and sitosterol acetate) were collected using excitation wavelengths of 229, 244 and 257 nm. In addition, visible Raman spectra of the fatty and resin acids were recorded. Resin compositions of heartwood and sapwood hexane extracts were determined using gas chromatography. Raman signals of both conjugated and isolated double bonds of all the model compounds were resonance enhanced by UV excitation. The oleophilic structures showed strong bands in the region of 1660-1630 cm(-1). Distinct structures were enhanced depending on the excitation wavelength. The UVRR spectra of the hexane extracts showed characteristic bands for resin and fatty acids. It was possible to identify certain resin acids from the spectra. UV Raman spectra collected from the solid wood samples containing wood resin showed a band at approximately 1650 cm(-1) due to unsaturated resin components. The Raman signals from extractives in the resin rich branch wood sample gave even more strongly enhanced signals than the aromatic lignin.     

Inner-shell excitation spectroscopy and fragmentation of small hydrogen-bonded clusters of formic acid after core excitations at the oxygen K edge

Inner-shell excitation spectra and fragmentation of small clusters of formic acid have been studied in the oxygen K-edge region by time-of-flight fragment mass spectroscopy. In addition to several fragment cations smaller than the parent molecule, we have identified the production of HCOOH.H+ and H3O+ cations characteristic of proton transfer reactions within the clusters. Cluster-specific excitation spectra have been generated by monitoring the partial ion yields of the product cations. Resonance transitions of O1s(C[double bond]O/OH) electrons into pi(CO)* orbital in the preedge region were found to shift in energy upon clusterization. A blueshift of the O1s(C[double bond]O)-->pi(CO)* transition by approximately 0.2 eV and a redshift of the O1s(OH)-->pi(CO)* by approximately 0.6 eV were observed, indicative of strong hydrogen-bond formation within the clusters. The results have been compared with a recent theoretical calculation, which supports the conclusion that the formic-acid clusters consist of the most stable cyclic dimer andor trimer units. Specifically labeled formic acid-d, HCOOD, was also used to examine the core-excited fragmentation mechanisms. These deuterium-labeled experiments showed that HDO+ was formed via site-specific migration of a formyl hydrogen within an individual molecule, and that HD2O+ was produced via the subsequent transfer of a deuterium atom from the hydroxyl group of a nearest-neighbor molecule within a cationic cluster. Deuteron (proton) transfer from the hydroxyl site of a hydrogen-bond partner was also found to take place, producing deuteronated HCOOD.D+ (protonated HCOOH.H+) cations within the clusters.     

Effects of spin transitions degeneracy in pulsed EPR of the fullerene C70 triplet state produced by continuous light illumination

X-band echo-detected electron paramagnetic resonance (ED EPR) spectra of triplet state of fullerene C(70) generated by continuous light illumination were found to correspond below 30K to a non-equilibrium electron spin polarization. Above 30K spectra are characteristic of Boltzmann equilibrium. Spectra were simulated fairly well with zero-field splitting parameters D=153 MHz and E and distributed within the range of 6-42 MHz. The origin of E distribution is attributed to the Jahn-Teller effect, which in glassy matrix is expected to depend on the local surrounding of a fullerene molecule (a so-called E-strain). In the center of ED EPR spectra a narrow hole was observed. With increase of the microwave pulse turning angle this hole transforms into a single narrow absorptive line. Numerical simulations by density matrix formalism confirm that central hole originates from a simultaneous excitation of both allowed electron spin transitions of the triplet (T(0)?T(+) and T(0)?T(-)), because of their degeneracy at this spectral position. Also explanations are given why this hole has not been observed in the previously reported experiments on continuous wave EPR and on ED EPR under laser pulse excitation.     

Intrachain electron and energy transfer in conjugated organometallic oligomers and polymers

The synthesis of polymers of the type (-Cz-C[triple chemical bond]C-PtL(2)-C[triple chemical bond]C-Cz-X-)(n) along with the corresponding model compounds (Ph-PtL'(2)-C[triple chemical bond]C-Cz)(2)-X-, where Cz=3,3'-carbazole, X=nothing, Cz, or F (2,2'-fluorene), L=PBu(3), and L'=PEt(3) are reported. The electronic spectra (absorption, excitation, emission, and ns-transient spectra) and the photophysics of these species in 2-methyltetrahyrofuran (2MeTHF) at 298 and 77 K are presented. Evidence for singlet electron and triplet energy transfer from the Cz chromophore to the F moiety are provided and discussed in detail. The rate for electron transfer is very fast (>4 x 10(11) s(-1)), whereas that for triplet-triplet energy transfer is much slower (approximately 10(3) s(-1)). This work represents a very rare example of studies that address electronic communication in the backbone of a conjugated organometallic polymer.     

Photoionization and ionic dissociation of the C3H3NS molecule induced by soft X‐ray near the C1s edge

Time of flight mass spectrometry, electron‐ion coincidence, and ion yield spectroscopy were employed to investigate for the first time the thiazole (C₃H₃NS) molecule in the gas phase excited by synchrotron radiation in the soft X‐ray domain. Total ion yield (TIY) and photoelectron‐photoion coincidence (PEPICO) spectra were recorded as a function of the photon energy in the vicinity of the carbon K edge (C1s). The C1s resonant transitions as well as the core ionization thresholds have been determined from the profile of TIY spectrum, and the features were discussed. The corresponding partial ion yields were determined from the PEPICO spectra for the cation species produced upon the molecular photodissociation. Additional ab initio calculations have also been performed from where relevant structural and electronic configuration parameters were obtained for this molecule.     

Competitive charge- and energy-transfer processes following core ionization in the Na- CO cluster

Anion-molecule clusters constitute a very suitable class of systems for studying intermolecular (interatomic) charge-transfer (CT) processes following core ionization. A weakly bound electron of the anion in these clusters can be easily transferred to the core-ionized molecule. The screening effect of this electron may have a dramatic impact on core-level spectra and even account for a breakdown of the quasiparticle picture of core ionization. This is demonstrated here by calculating the O1s(-1) and C1s(-1) core ionization spectra of the Na- CO cluster using an ab initio fourth-order Green's-function method. Interestingly, along with the CT processes in this cluster there exist also very efficient energy-transfer (ET) processes favored by the low excitation energies of Na-. These ET processes constitute an appreciable part of the electronic excitations following core ionization of Na- CO and exert thereby a strong influence on the spectra studied. The spectral features attributed to the ET processes are as pronounced as those attributed to the CT processes. Major differences in the behavior of CT and ET satellites as a function of the anion-molecule separation are found and explained. We compare also the O1s(-1) core ionization spectra of the Na- CO and Na- H2O clusters. Along with a certain similarity, these spectra exhibit substantial differences which are essentially attributed to the distinct cluster geometries.     

Vibrational assignment, structure and intramolecular hydrogen bond study of 3-amino-1-phenyl-2-buten-1-one

Fourier transform infrared and Fourier transform Raman spectra of 3-amino-1-phenyl-2-buten-1-one and its deuterated analogue were recorded in the regions 400-4,000 and 150-4,000 cm(-1), respectively. Furthermore, the molecular structure and vibrational frequencies of title compound were investigated by a series of density functional theoretical, DFT, and ab initio calculations at the post-Hartree-Fock (MP2) level. Although, the calculated frequencies are generally in agreement with the observed spectra but the DFT results are in much better quantitative agreement with the observed spectra than the MP2 results. The observed wavenumbers were analyzed and assigned to different normal modes of vibration of the molecule. The calculated geometrical parameters show a strong intramolecular hydrogen bond with a N...O distance of 2.621-2.668 A. This bond length is shorter than that of its parent, 4-amino-3-penten-2-one (with two methyl groups in the beta-position), which is in agreement with spectroscopic results. The topological properties of the electron density contributions for intramolecular hydrogen bond in 3-amino-1-phenyl-2-buten-1-one and 4-amino-3-penten-2-one have been analyzed in term of the Bader theory of atoms in molecules (AIM). These results also support the stronger hydrogen bond in the title compound with respect to the parent molecule.     

Electronic states of tetrahydrofuran molecules studied by electron collisions

Electronic states of tetrahydrofuran molecules were studied in the excitation energy range 5.5-10 eV using the technique of electron energy loss spectroscopy in the gas phase. Excitation from the two conformations, C(2) and C(s), of the ground state of the molecule are observed in the measured energy loss spectra. The vertical excitation energies of the (3)(n(o)3s) triplet state from the C(2) and C(s) conformations of the ground state of the molecule are determined to be 6.03 ± 0.02 and 6.25 ± 0.02 eV, respectively. The singlet-triplet energy splitting for the n(o)3s configuration is determined to be 0.31 eV. It is also found that excitation from the C(s) conformation of the ground state has a higher cross section than that from the C(2) conformation.     

Electron energy loss spectroscopy of van-der-Waals clusters

A method to measure electron energy loss spectra (EELS) of clusters with a high resolution (30 meV) has been developed and has been applied to some van der Waals clusters (Ar _n , Kr _n ). Structures have been found which relate to the excitation of atoms on the surface and inside the cluster. An influence of the cluster size on the spectra has been observed.     

Structural dynamics in floppy systems: ultrafast conformeric motions in Rydberg-excited triethylamine

Rotations about its three carbon-nitrogen bonds give triethylamine a complex, 3-dimensional potential energy landscape of conformeric structures. Electronic excitation to Rydberg states prepares the molecule in a high-energy, nonequilibrium distribution of such conformers, initiating ultrafast transitions between them. Time-resolved Rydberg electron binding energy spectra, observed using photoionization-photoelectron spectroscopy with ultrashort laser pulses, reveal these time-evolving structures. The time-dependent structural fingerprint spectra are assigned with the aid of a computational analysis of the potential energy landscape. Upon 209 nm electronic excitation to the 3p Rydberg state, triethylamine decays to 3s with a 200 fs time constant. The initially prepared conformer reacts to a mixture of structures with a time constant of 232 fs and settles into a final geometry distribution on a further subpicosecond time scale. The binding energy of the Rydberg electron is found to be an important determinant of the conformeric energy landscape.     

Theoretical Auger electron spectra of polymers by density functional theory calculations using model dimers

We propose a new approach for analysis of Auger electron spectra (AES) of polymers by density functional theory (DFT) calculations with the Slater's transition-state concept. Simulated AES and X-ray photoelectron spectra (XPS) of four polymers [(CH2CH2)n (PE), (CH2CH(CH3))n (PP), (CH2CH(OCH3))n (PVME), and (CH2CH(COCH3))n (PVMK)] by DFT calculations using model dimers are in a good accordance with the experimental ones. The experimental AES of the polymers can be classified in each range of 1s-2p2p, 1s-2s2p, and 1s-2s2s transitions for C KVV and O KVV spectra, and in individual contributions of the functional groups from the theoretical analysis.