Application of photoelectron spectroscopy to biologically active molecules and their constituent parts. II. 1,4-Benzodiazepines

The Hel photoelectron (PE) spectra of 5-phenyl-7-chloro-2H-1,4-benzodiazepin-2-one ( 1 ), its 1-methyl derivative ( 2 ), 3-hydroxy derivative ( 3 ), 1-methyl-3-hydroxy derivative ( 4 ), 3-(S)-methyl derivative ( 5 ), and 1-methyl-3-(S)-methyl derivative ( 6 ) have been recorded. The electronic structure of these compounds is discussed on the basis of the observed ionization energies, and of the semiempirical CNDO/2 calculations on model compounds 1a-6a , which have a hydrogen instead of the phenyl group in the 5-position. As a result the character of the seven highest occupied orbitals in 1–6 have been assigned.     

The Photoelectron Spectra of Ni,Pd, Pt-Diallyl

The He (I) photoelectron (PE.) spectra of bis (π-allyl)palladium (2a) , bis (π-allyl)platinum (3a) , bis (π-methallyl)palladium (2b) and bis (π-methallyl)-platinum (3b) have been recorded and compared with the PE. spectra of bis (π-allyl)nickel (1a) and bis (π-methallyl)nickel (1b) . By use of the He (II) PE. spectra 2a, 2b and 3b and correlations between the PE. spectra of 1–3 it is possible to assign the first seven to eight transitions in the PE. spectra of 1–3 . In contrast to previous assignments it is shown that the first band in the PE. spectrum of 1a corresponds to the ejection of an electron from 7a_u, a pure ligand orbital. The assignment proposed is supported by semiempirical calculations of the INDO-type by considering the relaxation effects explicitly using the ΔSCF and transition operator method.     

HeI photoelectron spectroscopic study of the electronic structure of SSF2 and FSSF compounds

HeI photoelectron (PE) spectra are re-recorded for SSF₂ and FSSF. The assignment of bands has been made with the aid of band shapes, band intensities and ab initio calculations. In the PE spectrum of SSF₂, two sharp peaks at 10.48 and 11.22 eV are considered to result from through-space interaction of lone-pair orbitals in the two S atoms and two sharp peaks at 12.50 and 12.90 eV from through-space interaction of lone-pair orbitals in the two F atoms. The larger splitting of the S atoms can be attributed to the larger 3p orbital of S. The lack of sharp peaks in the PE spectrum of FSSF shows that there is no orbital which embodies the character of a lone-pair. So the PE spectra of SSF₂ and FSSF are examples embodying through-space interaction of lone-pair orbitals.     

SiO_2/PE/Bi_2S_3核壳结构纳米颗粒的合成与性能(英文)

以多层电解质作为微型反应器,制备了SiO2/Polyelectrolyte(PE)/Bi2S3核壳纳米粒子。XRD结果表明Bi2S3颗粒属于正交晶系。由透射电镜和场发射扫描电镜照片可知,在直径为640nm左右的SiO2表面覆盖了厚度35nm的Bi2S3壳层。红外光谱分析结果表明硅烷网络在结构上发生了变化(SiO2表面的硅烷醇键沉积在Bi2S3的表面)。SiO2核和SiO2/PE/Bi2S3的紫外-可见吸收光谱显示在900nm存在典型吸收边。     

Circular dichroism spectra and absolute configuration of some aryl methyl sulfoxides

The absorption and circular dichroism (CD) spectra of three aryl sulfoxides, i.e. (-)-(S)-1-naphthyl methyl sulfoxide, (S)-1, (-)-(S)-1-(2-methyl)naphthyl methyl sulfoxide, (S)-2 and (-)-(S)-9-phenanthryl methyl sulfoxide, (S)-3, have been interpreted by means of the coupled oscillator model formulated by DeVoe. Theoretical spectra have been calculated starting from input geometries provided by molecular mechanics (MMX) calculations and by employing standard spectroscopic parameters to describe the allowed transitions of the aromatic and the sulfoxide chromophores. The satisfactory agreement between the predicted and experimental spectra allows us to confirm the configurational assignment of these compounds as (-)/(S). The analysis of CD spectra, affording the right assignment of the absolute configuration (AC) of the alkyl aryl sulfoxides, then offers a practical alternative to the more complex vibrational circular dichroism spectroscopy and ab initio optical rotation calculation techniques that have been used very recently to assign the AC of (-)-2 and (-)-3.     

Photoelectron spectroscopy of heterocycles. Azaindenes and azaindolizines

The HeI photoelectron (PE) spectra of indole ( 1 ), benzimidazole ( 2 ), indazole ( 3 ), 3-chloro-indazole ( 4 ), imidazo[1,2-b]pyridazine ( 5 ), 6-chloroimidazo[1,2-b]pyridazine ( 6 ), 2-phenyl-imidazo[1,2-b]pyridazine ( 7 ), 2-phenyl-6-chloroimidazo[1,2-b]pyridazine ( 8 ), tetrazolo[1,2-a]-pyridine ( 9 ) and 8-cyanotetrazolo[1,5-a]pyridine ( 10 ) have been recorded. The spectra of 2–10 are of special interest for studying lone pair interactions. The assignment of the PE spectra submitted here, conjointly with the electronic structure of the studied compounds is discussed on the basis of molecular orbital calculations.     

Asymmetry in platinum acetylide complexes: confinement of the triplet exciton to the lowest energy ligand

To determine structure-optical property relationships in asymmetric platinum acetylide complexes, we synthesized the compounds trans-Pt(PBu3)2(C[triple bond]CC6H5)(C[triple bond]C-C6H4-C[triple bond]CC6H5) (PE1-2), trans-Pt(PBu3)2(C[triple bond]CC6H5)(C[triple bond]C-C6H4-C[triple bond]C-C6H4-C[triple bond]CC6H5) (PE1-3) and trans-Pt(PBu3)2(C[triple bond]C-C6H4-C[triple bond]CC6H5)(C[triple bond]C-C6H4-C[triple bond]C-C6H4-C[triple bond]CC6H5) (PE2-3) that have different ligands on either side of the platinum and compared their spectroscopic properties to the symmetrical compounds PE1, PE2 and PE3. We measured ground state absorption, fluorescence, phosphorescence and triplet state absorption spectra and performed density functional theory (DFT) calculations of frontier orbitals, lowest lying singlet states, triplet state geometries and energies. The absorption and emission spectra give evidence the singlet exciton is delocalized across the central platinum atom. The phosphorescence from the asymmetric complexes comes from the largest ligand. Time-dependent (TD) DFT calculations show the S1 state has mostly highest occupied molecular orbital (HOMO) --> lowest unoccupied molecular orbital (LUMO) character, with the LUMO delocalized over the chromophore. In the asymmetric chromophores, the LUMO resides on the larger ligand, suggesting the S1 state has interligand charge transfer character. The triplet state geometries obtained from the DFT calculations show distortion on the lowest energy ligand, whereas the other ligand has the ground state geometry. The calculated trend in the triplet state energies agrees very well with the experimental trend. Calculations of triplet state spin density also show the triplet exciton is confined to one ligand. In the asymmetric complexes the spin density is confined to the largest ligand. The results show Kasha's rule applies to these complexes, where the triplet exciton moves to the lowest energy ligand.     

An investigation of terpene hydrocarbons of the carane series by photoelectron spectroscopy

2- and 3-Carenes and carane have been studied by PE spectroscopy. On the basis of an analysis of orbital interactions and information obtained from the PE spectra of model compounds an assignment has been made of the bands corresponding to ionization from the molecular orbitals of the double bond and of the cyclopropane ring.     

Absolute configurations, predominant conformations, and tautomeric structures of enantiomeric tert-butylphenylphosphinothioic acid.

Vibrational absorption and circular dichroism spectra of dextrorotatory, levorotatory, and racemic mixture of tert-butylphenylphosphinothioic acid have been measured in CCl(4) solutions in the 2000-900 cm(-1) region. The conformations for both tautomeric structures of (S)-tert-butylphenylphosphinothioic acid are investigated using the B3LYP functional with the 6-31G* basis set. For the most stable conformation, the absorption and VCD spectra are predicted ab initio using the B3LYP functional with 6-31G*, 6-311G(2d, 2p), 6-31+G, and 6-311G(3df, 3pd) basis sets. A different functional, B3PW91, was also used with the 6-31G* basis set. The predicted spectra are compared to the experimental spectra. The comparison indicates that (-)-tert-butylphenylphosphinothioic acid is of the (S)-configuration and exists in only one tautomeric structure and one conformation in CCl(4) solution.     

Ultrafast dynamics in thiophene investigated by femtosecond pump probe photoelectron spectroscopy and theory

A hybrid of a time-of-flight mass spectrometer and a time-of-flight "magnetic-bottle type" photoelectron (PE) spectrometer is used for fs pump-probe investigations of the excited state dynamics of thiophene. A resonant two-photon ionization spectrum of the onset of the excited states has been recorded with a tunable UV laser of 190 fs pulse width. With the pump laser set to the first intense transition we find by UV probe ionization first a small time shift of the maxima in the PE spectrum and then a fast decay to a low constant intensity level. The fitted time constants are 80+/-10 fs, and 25+/-10 fs, respectively. Theoretical calculations show that upon geometry relaxation the electronic state order changes and conical intersections between excited states exist. We use the vertical state order S1, S2, S3 to define the terms S1, S2, and S3 for the characterization of the electron configuration of these states. On the basis of our theoretical result we discuss the electronic state order in the UV spectra and identify in the photoelectron spectrum the origin of the first cation excited state D1. The fast excited state dynamics agrees best with a vibrational dynamics in the photo-excited S1 (80+/-10 fs) and an ultrafast decay via a conical intersection, presumably a ring opening to the S3 state (25+/-10 fs). The subsequently observed weak constant signal is taken as an indication, that in the gas phase the ring-closure to S0 is slower than 50 ps. An ultrafast equilibrium between S1 and S2 before ring opening is not supported by our data.     

Functional polymers and sequential copolymers by phase transfer catalysis. XXVI. Synthesis and characterization of thermotropic liquid crystalline polypodants

Thermotropic liquid crystalline (LC) polyethers and copolyethers have been synthesized from 4,4′-dihydroxy-α-methylstilbene (HMS) and α,ω-dichlorooligo(oxyethylene)s having between 2 and 5 as well as 8.7 oxyethylene units. Copolyethers were prepared from a 1:1 mol/mol ratio of two dissimilar spacers. These polymers have been prepared by a phase transfer catalyzed (PTC) polyetherification of bisphenols with these electrophiles by utilizing 50 mol% tetrabutylammonium hydrogen sulfate per phenol group. Kinetic experiments with either 5 or 50 mol% catalyst vs phenol groups in the polyetherification of 4,4%-isopropylidenediphenol with 2-chloroethyl ether have shown that a change in catalyst primarily affects the rate of reaction, with 50 mol % being faster. The prepared polyethers and copolyethers are soluble in common organic solvents. Both polyethers and copolyethers are crystalline. Polymers prepared to contain tetraoxyethylene spacers exhibit monotropic LC behavior. Copolymers prepared to contain tri- and tetraoxyethylene spacers (1 : 1 mol/mol) [PE34] were the only polymers exhibiting enantiotropic LC behavior. Longer spacers tend to destabilize the phase transitions, as suggested by the dependence of thermal transition temperatures upon the differential scanning calorimeter rate. All prepared polymers act as podants in solution, measured by picrate extraction experiments. Solid state complexes have been prepared from the polymer with a pentaoxyethylene spacer [PE5] and PE34 with LiCF₃SO₃. PE5 can dissolve LiCF₃SO₃ in the range of 0.21–2.2 mol salt/mol polymer (m.r.u.) [S/P] without the observation of free salt. PE5 complexes of/or below S/P of 0.43, upon annealing at room temperature, exhibited the two melting transitons observed in the polymer alone. PE5 complexes of/or above S/P of 0.77 only exhibited a T_g. The T_g of PE5 complexes were found to change nonlinearly with S/P, while T_m1 changed linearly. T_m2 was independent of S/P. Only one complex with PE34 gave two transitions (T_m2,Tⁱ) in dynamic DSC experiments. Other PE34 complexes followed a behavior similar to PE5 complexes.     

Theoretical investigation of one- and two-photon absorption properties of platinum acetylide chromophores

In this paper, we have theoretically investigated bis((4-phenylethynyl)phenyl) ethynyl)bis(trimethylphosphine)platinum(II) (PE2) and its analogs three platinum acetylide complexes (1-3) that feature highly pi-conjugated ligands (alkynyl-dimethylfluorene substituted with electron-donating or -withdrawing moieties). The geometrical and electronic structures are calculated at the ECP60MWB//6-31G*(H, C, P, N, S) basis set level by the density functional theory (DFT) method; one-photon absorption properties have been calculated by using time-dependent DFT (TDDFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods, and two-photon absorption (TPA) properties are obtained with the ZINDO/sum-over-states method. The values of beta(sp) and beta(d) for Pt are adjusted to -1 eV and -28.5 eV, respectively, to make one-photon absorption spectra calculated by ZINDO closest to the experimental data and TDDFT results. The calculated results indicate that all molecules in this work (involving cis isomers of molecules 1-3) take on two TPA peaks in the 600-800 nm region. The peak at 700-750 nm should not be simply attributed to the appearance of noncentrosymmetric cis isomers in solution, although trans and cis isomers adhere to a different selection rule. Every TPA peak results from its transition character. Molecules 1-3 show greater two-photon absorption strength compared with PE2 and retain good transparency.     

Emission spectra and electronic energy levels of the rotational isomers of pyridinecarboxaldehyde vapors

Emission and excitation spectra of 2-, 3- and 4-pyridinecarboxaldehyde (2-, 3- and 4-PCA, respectively) vapors have been measured at different temperatures and compared to one another. The emission spectra of these vapors are shown to consist of the T(1)(n, pi) --> S(0) phosphorescence accompanied by the weak thermally activated S(1)(n, pi) --> S(0) delayed fluorescence. Two peaks originating from the two rotamers (syn and anti) have been identified in the fluorescence, phosphorescence and excitation spectra of 3-PCA vapor. Analyses of the temperature dependence and vibrational structure of the spectra of 3-PCA vapor provide the syn-anti energy difference of 190 +/- 30 cm(-1) in the T(1) (n, pi) state, 200 +/- 30 cm(-1) in the S(1)(n, pi) state, and 290 +/- 35 cm(-1) in the ground state. The ground-state energy difference is in agreement with the result of density functional theory (DFT) calculation for 3-PCA vapor. DFT calculation demonstrated also that the syn rotamer exists as a less stable isomer in the ground state for 2- and 3-PCA vapors.     

Zero kinetic energy photoelectron study of SO2+(X2A1) using coherent extreme ultraviolet radiation

Using our newly built extreme ultraviolet (XUV) photoelectron and photoion spectrometer, we have obtained the pulsed field ionization zero kinetic energy (ZEKE) photoelectron spectra of SO2+(X2A1)<--SO2(X1A1) by coherent XUV radiation in the energy range of 12.29-12.82 eV. The adiabatic ionization potential (IP) of SO2 is 12.3458+/-0.0002 (eV), which was determined by comparing the partially resolved rotational branch contour with the simulated one. Besides the bending vibrational mode (upsilon2) which was found to be exclusive in the photoelectron spectra (PE) reported previously, we also observed the other two modes: the symmetric stretching (upsilon1) and the antisymmetric stretching (upsilon3) vibrations. The fundamental of the symmetric stretching (upsilon(1)) is 1057 cm(-1) and the overtone of the antisymmetric stretching (2upsilon(3)) is 2494 cm(-1). The new vibrational progressions (upsilon(1)00)+, (1upsilon(2)0)+, (2upsilon(2)0)+, and (0upsilon(2)2)+ have also been observed, and these new observations suggested that the irregular structure of (0upsilon(2)0)+ assigned to the previous PE spectra should be reconsidered. The comparison of the intensities of these vibrational bands with the calculated Franck-Condon factors with harmonic approximation was also made.     

Cyclic Acetals. Structural Analysis of 1,3-Dioxepine and Related Compounds

The He(I) PE spectra of 1,3-dioxepine ( 1 ) and the related bicyclic acetals 1,3,7,7-tetramethyl-2,11-dioxabicyclo[4.41]undeca-3,5-dien-10-one ( 2 ) and 1,3,7,7-tetramethyl-10-methylidene-2,11-dioxabicyclo[4.4.1]undeca-3,5-diene ( 3 ) have been recorded and analyzed. Interpretation of the PE data indicate strong orbital interactions between the diene and acetal moieties in 1 . Different conformations have been evaluated by a joint MMP2 molecular mechanics and ab initio molecular orbital analysis, which shows 1 to prefer a slightly boat-shaped conformation with the diene part being planar and the CH₂ group placed considerably out-of-plane. The bicyclic acetals 2 and 3 show a frontier orbital picture similar to 1 superimposed with the characteristics of the C?O and C?C groups, respectively. The crystal structure of the keto-acetal 2 was determined by an X-ray analysis.     

The orbital sequence in cyclic 1,3-diketones

The He(I) photoelectron (PE) spectra of the cyclic 1,3-diketones 1–5 have been recorded. Based on a comparison between experimental and calculated (MINDO/3) results it is shown, that in all cases the n_(A) orbital is on top of the n₊(S) orbital. This sequence is confirmed by the comparison between the PE spectra of 1–5 with those of the corresponding vic.triketones 6–10.     

The He(Iα) Photoelectron Spectra of Substituted 1,2-Dithietes

The He(Iα) photoelectron (PE.) spectra of a series of substituted 1,2-dithietes have been recorded and assigned with respect to the orbital sequence derived from an STO-3G model calculation and by correlation with the PE. spectra of related compounds. The results provide additional support for the presence of a closed, four-membered ring moiety in all the 1,2-dithietes investigated. In all cases the two highest occupied molecular orbitals are b₂(π)= HOMO, a₂(π), with exception of 3,4-bis(trifluoromethyl)-1,2-dithiete where the sequence b₂(π), a₂(π) or a₂(π), b₂(π) is uncertain.     

The Electronic Structure of Phenylene and Naphthylene Bicyclobutanes. Photoelectron spectroscopy and model calculations

The photoelectron (PE.) spectra of 1,2,3-methenoindane ( 2 ), 1,2,3-metheno-2,3-dihydro-1H-cyclopenta [b]naphthalene ( 3 ) and 1,2,3-metheno-2,3-dihydro-1H-phenalene ( 4 ) are investigated. The PE. spectrum of 1,3-methano-2,3-dihydrophenalene ( 7 ) is reported and compared with that of 4 . The experimental results are analyzed in terms of empirical correlation diagrams and the results of semiempirical MINDO/3 and CNDO/S calculations. The analysis indicates that the strong impact of the bicyclobutylene group on the spectroscopic properties of the aromatic π-systems in 2 , 3 and 4 is due to hyperconjugative interactions involving bicyclobutane Walsh orbitals.     

Absolute configuration of tert-butyl-1-(2-methylnaphthyl)phosphine oxide

The enantiomers of tert-butyl-1-(2-methylnaphthyl)phosphine oxide 1 have been separated using a homemade HPLC column and an analytical gradient system. Vibrational absorption and circular dichroism spectra for both enantiomers have been measured in CD2Cl2 and CH2Cl2 solutions in the 2000-900 cm(-1) region. The fully relaxed potential energy surface of (S)-tert-butyl-1-(2-methylnaphthyl)phosphine oxide, obtained using the B3LYP functional with a 6-31G basis set, indicated two stable conformers with their populations in a approximately 2:1 ratio. The vibrational absorption and VCD spectra are predicted for these two conformers using the B3LYP functional with a 6-31G basis set. The comparison of predicted and experimental spectra indicated that (+)-tert-butyl-1-(2-methylnaphthyl)phosphine oxide is in the (S)-configuration. This assignment is supported by the ab initio prediction of positive optical rotation for the most stable conformer with an (S)-configuration and the nonequivalence sense of the tert-butyl group chemical shift observed in the 1H NMR spectrum of this enantiomer measured in the presence of (+)-(S)-mandelic acid as a chiral solvating agent.     

Reactions between CO and small molybdenum suboxide cluster anions

Reaction products resulting from small molybdenum suboxide cluster anions and carbon monoxide were studied with both mass spectrometry and anion photoelectron (PE) spectroscopy. In addition to the C6O6- product proposed previously, a number of unsaturated carbonyls were identified as terminal products in these reactions. A new PE spectrum of what may be C6O6-, in which the contribution from the Fe(CO)4- contaminant is subtracted, is reported. Additionally, the PE spectra of Mo(CO)5-, MoO(CO)3-, and MoO2(CO)n- (n=1 and 2) are presented, along with a new PE spectrum of an additional contaminant, Ni(CO)3-. Evidence of photodissociation of MoO(CO)3- to MoO-+3 CO is observed in the PE spectrum of MoO(CO)3-.