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1.
Murakami H Kawabuchi A Matsumoto R Ido T Nakashima N 《Journal of the American Chemical Society》2005,127(45):15891-15899
The shuttling process of alpha-CyD in three rotaxanes (1-3) containing alpha-cyclodextrin (alpha-CyD) as a ring, azobenzene as a photoactive group, viologen as an energy barrier for slipping of the ring, and 2,4-dinitrobenzene as a stopper was investigated. The trans-cis photoisomerization of 1 by UV light irradiation occurred in both DMSO and water due to the movement of alpha-CyD toward the ethylene group, while the photoisomerization of 2 occurred in DMSO, but not in water. No photoisomerization was observed for 3 in both water and DMSO. The activation parameters of 1 and 1-ref in DMSO are subject to a compensation relation between deltaS(double dagger) and deltaH(double dagger); however, in water, the deltaS(double dagger) terms are not compensated by the deltaH(double dagger) terms. Alternating irradiation of the UV and visible lights resulted in a reversible change in the induced circular dichroism (ICD) bands of trans-1 and cis-1. In contrast, after the UV light irradiation, the ICD band of trans-2 decreased without the appearance of any bands of cis-2. The NMR spectra of 2 in DMSO showed coalescence of the split signals for the methylene and for the viologen protons due to the shuttling of alpha-CyD. Both the NOE differential spectra for cis-1 in water after UV light irradiation and 2 in DMSO after heating to 120 degrees C showed the negative NOE peaks assigned to interior protons of alpha-CyD, suggesting that alpha-CyD in cis-1 exists at the one ethylene moiety, and alpha-CyDs in cis-2 and 2 heated in DMSO exist at the propylene moieties. 相似文献
2.
Ya. N. Malkin N. A. Lysak S. A. Tikhomirov G. B. Tolstorozhev V. A. Lokshin V. A. Kuz'min 《Russian Chemical Bulletin》1987,36(9):1979-1982
Conclusions Photoexcitation of a solution of 6-nitrospiro(2H-l-benzopyran)-2,2-isobenzofuran under picosecond laser photolysis conditions leads to cleavage of a C-O bond in a Franck-Condon state and formation of a shortlived cis-cisoid isomer of the merocyanine form of the spiropyran.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2129–2132, September, 1987. 相似文献
3.
Fourier-Transform infrared (FTIR) spectroscopy and surface energy analysis (contact angle measurements) have been performed as a means of identification and quantification of the functionalization of polystyrene surfaces upon vacuum ultraviolet- (VUV-) photochemically initiated oxidation. Photochemical oxidation was performed in the presence of water vapor and molecular oxygen using a pulsed Xe2-excimer radiation source (lambda(exc): 172 nm). Surface oxidation was studied as a function of two parameters: irradiation time and distance between sample and radiation source. During the first 1-2 min of irradiation, an increase of the concentrations of hydroxyl (OH) and carbonyl (C=O) groups on the surface was observed, both reaching limiting values. As expected, the rate of oxidation diminished exponentially with increasing distance between the radiation source and the surface of the polystyrene film. Changes in the surface energy due to the introduction of these polar (i.e. OH and C=O) groups were also determined. The densities of the functional groups decreased upon washing with acetonitrile, and analysis of the washing solution by means of gas chromatography-mass spectrometry (GC-MS) revealed the presence of a large number of products. The application of pulsed Xe2-excimer radiation sources as a valuable alternative to conventional means (i.e. laser and plasma) for the photochemical oxidation and surface modification of polystyrene is discussed. 相似文献
4.
反应体系的势能面,对了解反应的微观过程起着重要的作用,它的特征决定了化学反应的机理.原则上,由反应体系的Schrodinger方程的解,可得到体系能量随核间距变化的函数,从而获得势能面.除少数简单反应外,几乎无法精确求得复杂反应体系的势能面.因而,除从头算法外,人们先后发展了计算势能面的一些半经验方法.对某一反应,文献中可能记载好几个势能面,因此,在分析反应或计算反应的各物理量时,应当说明所应用的是何种势能面.我们曾指出,过渡态熵的可靠性,有赖于提供过渡态参数的势能面.本文从下述基元反应 相似文献
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6.
Pederzoli M Pittner J Barbatti M Lischka H 《The journal of physical chemistry. A》2011,115(41):11136-11143
Ab initio nonadiabatic dynamics simulations of cis-to-trans isomerization of azobenzene upon S(1) (n-π*) excitation are carried out employing the fewest-switches surface hopping method. Azobenzene photoisomerization occurs purely as a rotational motion of the central CNNC moiety. Two nonequivalent rotational pathways corresponding to clockwise or counterclockwise rotation are available. The course of the rotational motion is strongly dependent on the initial conditions. The internal conversion occurs via an S(0)/S(1) crossing seam located near the midpoint of both of these rotational pathways. Based on statistical analysis, it is shown that the occurrence of one or other pathway can be completely controlled by selecting adequate initial conditions. 相似文献
7.
A. L. Attwood D. M. Murphy J. L. Edwards T. A. Egerton R. W. Harrison 《Research on Chemical Intermediates》2003,29(5):449-465
The formation of a series of oxygen-centred radicals on different TiO2 samples (P25 and two different rutile materials) under various conditions was investigated using X-band c.w. Electron Paramagnetic Resonance (EPR) spectroscopy. The radicals were formed either on thermally-reduced TiO2, or by UV irradiation of the oxide under an oxygen atmosphere. The nature and stability of the radicals was also explored as a function of surface hydration. On thermally reduced TiO2, containing surface and bulk Ti3+ centres, oxygen adsorption at 300 K results in the preferential formation and stabilisation of O2
- anions on the P25 surface, but O- and O3
- anions are generated on the rutile surfaces. Superoxide anions (O-) and trapped holes (O2
-) were also identified after photo-irradiation of the thoroughly dehydrated TiO2 samples under oxygen. The O- anions were only visible at low temperatures under continuous irradiation, while the O2
- anions were stable for days at 300 K. By comparison, on fully hydrated surfaces, no stable oxygen centred radicals could be detected on P25, while O2
- anions were easily observed on the rutile surfaces. On partially hydrated P25, the O-, O2
- and HO2 anions were detected after UV irradiation at 77 K; all radicals decayed upon warming to 298 K. On partially hydrated rutile, the O- and O2
- anions were detected and, unlike the case for P25, were found to be stable for days under the same conditions. The results illustrate the varied formation and stability of the oxygen centred radicals on TiO2 surfaces depending on the pretreatment conditions. 相似文献
8.
Zhi Zheng Jie Xu Youyi Sun Jingli Zhou Biao Chen Qijin Zhang Keyi Wang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(10):3210-3219
A series of optically active methacrylic homopolymers, poly[(4‐{4′‐[(S)‐2‐methyl‐1‐butyloxycarbonyl]phenylazo}phenoxyl)x‐methylene methacrylate] (x = 0, 2, 6, or 11), were synthesized. The structures of the polymers were characterized by IR, 1H NMR, UV, differential scanning calorimetry, and gel permeation chromatography. The chiroptical properties of the polymers in films were investigated with circular dichroism (CD) measurements. The CD and UV spectra of the films suggested that CD absorptions occurred in the films of the polymers with long spacers (x = 6 or 11) but not in the films of the polymers with short spacers (x = 0 or 2). After irradiation with linearly polarized light at 442 nm, the CD values were amplified in all the polymeric films. The amplificatory values of the CD bands in the absorption region (260–360 nm) of azobenzene chromophores suggested that the spacer length had an effect on both the transfer of chirality and photoinduced chirality in the polymeric films. The largest level of photoinduced chirality was induced in the polymer containing six methylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3210–3219, 2006 相似文献
9.
Galindo MA Houlton A Clegg W Harrington RW Dobado J Santoyo-Gonzalez F Linares F Romero MA Navarro JA 《Chemical communications (Cambridge, England)》2008,(32):3735-3737
The cyclic trinuclear system, [(en)(3)Pd(3)(4,7-phen)(3)](6+), undergoes a ligand exchange reaction with 5-R-2-hydroxypyrimidine derivatives (HRpymo; R = ethynylferrocene, 5-(dimethylamino)-N-(2-propynyl)-1-naphthalene sulfonamide) to give [(en)(3)Pd(3)(4,7-phen)(2)(Rpymo)](5+), functional supramolecular receptors of mononucleotides. 相似文献
10.
A series of azobenzenes was studied using ab initio methods to determine the substituent effects on the isomerization pathways. Energy barriers were determined from three-dimensional potential energy surfaces of the ground and electronically excited states. In the ground state (S(0)), the inversion pathway was found to be preferred. Our results show that electron donating substituents increase the isomerization barrier along the inversion pathway, whereas electron withdrawing substituents decrease it. The inversion pathway of the first excited state (S(1)) showed trans --> cis barriers with no curve crossing between S(0) and S(1). In contrast, a conical intersection was found between the ground and first excited states along the rotation pathway for each of the azobenzenes studied. No barriers were found in this pathway, and we therefore postulate that after n --> pi (S(1) <-- S(0)) excitation, the rotation mechanism dominates. Upon pi --> pi (S(2) <-- S(0)) excitation, there may be sufficient energy to open an additional pathway (concerted-inversion) as proposed by Diau. Our potential energy surface explains the experimentally observed difference in trans-to-cis quantum yields between S(1) and S(2) excitations. The concerted inversion channel is not available to the remaining azobenzenes, and so they must employ the rotation pathway for both n --> pi and pi --> pi excitations. 相似文献
11.
The reaction of metallocycle cluster compounds Mx?1C4H8(M = Ti; V; Cr; Mo; W or Fe) with nitrobenzene yields aniline and azobenzene, while the reaction with azobenzene yields aniline only. By means of mass spctrometry 15N isotope fractionation in a region where a natural abundance of the nitrogen isotope occurs it was stated that aniline and azobenzene arise independently of each other, and the reaction follows the nitrene mechanism. On the other hand aniline from azobenzene is formed as a result of -NN- cleavage to the multimetallic cluster centre. 相似文献
12.
Using density-functional-based molecular dynamics simulations, we have performed comparative studies of the trans-cis isomerizations of azobenzene and bridged azobenzene (B-Ab) 5,6-dihydrodibenzo[c,g][1,2]diazocine induced by nπ* electronic excitation. The quantum yields found in our calculations, 45% for the bridged azobenzene versus 25% for azobenzene, are consistent with the experiment. Both isomerization processes involve two steps: (1) Starting from the trans structure, each molecule moves on its S(1) excited-state potential energy surface, via rotation around the NN bond, to an avoided crossing near the S(1)/S(0) conical intersection, where de-excitation occurs. (2) Subsequently, in the electronic ground state, there is further rotation around the NN bond, accompanied by twisting of the phenyl rings around their CN bonds, until the cis geometry is achieved. Because of its lower symmetry and smaller initial CNNC dihedral angle, the bridged azobenzene has a much shorter lifetime for the S(1) excited state, about 30 fs, as compared to about 400 fs for azobenzene. However, we find that the complete isomerizations have approximately the same time scales. Although the bridging feature in trans-B-Ab does not hinder rotation around the NN bond in step 1, it makes twisting of the two phenyl rings around the CN bonds much slower in step 2. 相似文献
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14.
Azobenzene-functionalized nanotubes recognized and attached onto well-defined complementary regions of thiolated alpha-CD SAM/Au substrates via host-guest molecular recognition. The binding between the azobenzene nanotubes and the alpha-CD SAM/Au substrates was controlled by UV irradiation. The light-induced attachment-detachment of the azobenzene nanotubes on the alpha-CD SAMs was reversible. Some of the nanotubes were capable of interconnecting two Au substrates. This smart building block may be applied to build photoactive nanometer-sized mechanical switches in electronics. 相似文献
15.
Thermolysis of azobenzene in a melt and in solution results in the formation of aniline. The possible directions of the reaction are considered. Comparison of the enthalpies of the reaction proves that the cleavage of a -bond in the N=N group to form a biradical intermediate is thermodynamically more favorable than that of a C-N -bond.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1562–1564, September, 1993. 相似文献
16.
《Bioelectrochemistry and bioenergetics (Lausanne, Switzerland)》1993,29(3):337-346
The activity of diaphorase (from Bacillus stearothermophilus) immobilized on glassy carbon (GC) electrodes was determined by analyzing the catalytic currents for oxidation of the immobilized enzyme using digital simulation techniques, which gives the concentration of the active enzyme at the electrode surface. Results show that the immobilization by the cross-linking reaction with glutaraldehyde deactivates the enzyme and only about 10% of the total enzyme remains active at the electrode surface. 相似文献
17.
Hofmann M 《Inorganic chemistry》2008,47(13):5546-5548
Computations suggest that in contrast with small models the active site geometry of reduced dimethyl sulfoxide reductase might prefer a triplet over a singlet electronic state. 相似文献
18.
Haruhisa Akiyama Kazuaki Kudo Kunihiro Ichimura 《Macromolecular rapid communications》1995,16(1):35-41
Polymethacrylates with laterally attached azobenzenes were prepared to cause molecular reorientation of this chromophore in their thin films by linearly polarized irradiation with an exposure energy of less than ca. 100 mJ/cm2. A homogeneous alignment was induced by assembling a nematic liquid crystal cell using a substrate plate covered with the photoirradiated films. The alignment direction of the cell was controlled by changing the electric vector of the actinic light. 相似文献
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20.
Hiroaki Horiuchi Toru Fukushima Changli Zhao Tetsuo Okutsu Shoji Takigami Hiroshi Hiratsuka 《Journal of photochemistry and photobiology. A, Chemistry》2008,198(2-3):135-143
Conformational change of the main chain of poly(methylphenylsilane) functionalized with pendant azobenzene has been studied in the solution and in the film state. The conformation of the main chain was found to depend on the molar ratio of the Si units with and without the pendant azobenzene moiety. The inflection region for the conformational change was 0.3–0.5 of the molar ratio. The conformation of the main chain changed by the photoisomerization of the pendant azobenzene moiety in the film state. The efficiency of the conformational change of the main chain increased with the decrease of the molar ratio, accompanied by the highest final value of degree of the conformational change at the molar ratio of 0.5. The reverse conformational change was induced by heating. 相似文献