- Photocalorimetry. 6. Enthalpies of Isomerization of Norbornadiene and of Substituted Norbornadienes to Corresponding Quadricyclenes
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The enthalpies of isomerization of norbornadiene and of several substituted norbornadienes to the corresponding quadricyclenes have been determined by the method of photocalorimetry.This method also gives f, the percent of adsorbed light energy of a given wavelength that is stored chemically as a consequence of the photoinduced isomerization.The results for 25 deg C are as follows (compound, solvent, ΔH in kcal mol-1, fwavelength, nm): norbornadiene, cyclohexane, 14.0 +/- 1, f313 = 15.0 +/- 1percent: 2,3-bis(carbomethoxy)norbornadiene, acetonitrile, 25.2 +/- 3.5, f313 = 12.4 +/- 2.2percent; 2,3-dicyanonorbornadiene, acetonitrile, 22.0 +/- 2.3, f313 = 11.2 +/- 1.9percent; 1,2,3-trimethyl-5,6-dicyanonorbornadiene, acetonitrile, 21.0 +/- 2.0, f366 = 15.5 +/- 1.7percent.The position of the first absorption band shifts progressively to longer wavelengths in the above sequence, and the results show that such shifting toward the solar insolation region does not impair the energy storage ability of the system.For the parent, norbornadine system, it was necessary to use acetophenone as sensitizer, and it is possible that minor secondary photolysis effects led to the relatively low ΔH value; the value has the merit that it is the practical one for conditions relevant to actual solar energy storage.
- Harel, Yaacov,Adamson, Arthur W.,Kutal, Charles,Grutsch, Paul A.,Yasufuku, Katsutoshi
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- A solar-energy-derived strained hydrocarbon as an energetic hypergolic fuel
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Quadricyclane (QC), synthesized from photoisomerization and commonly used for solar-energy conversion and storage, is found to be an excellent hypergolic fuel. The ignition delay time of QC-N2O4 is 29 ms, which is decreased to 18 ms by addition of boron nanoparticles. Importantly, quadricyclane has 18.9% higher specific impulsion than currently used but dangerous dimethylhydrazine. This journal is
- Pan, Lun,Feng, Ren,Peng, Hao,Xiu-Tian-Feng,Zou, Ji-Jun,Wang, Li,Zhang, Xiangwen
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- A Silica-supported Inorganic Photosensitizer
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Adsorption of 2+ (bipy = 2,2'-bipyridine) onto silica gel does not adversely affect the efficiency with which this transition metal complex photosensitizes the valence isomerization of norbornadiene to quadricyclene.
- Grutsch, Paul A.,Kutal, Charles
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- Mechanistic Approach to the Sensitization Process of Aromatic Ketones in the Isomerization between Norbornadiene and Quadricyclane
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The quantum yields for norbornadiene(N)-->quadricyclane(Q) and Q-->N isomerization were determined in acetonitrile using several substituted benzophenones (BPs) as triplet sensitizers.For the N-->Q isomerization, BPs with electron-donating substituents exhibited higher quantum efficiency (0.4-0.6) than BPs with electron-accepting substituents.The quantum yields for Q-->N isomerization increased with electron-accepting ability of the substituents on BPs, but were lower than 0.1.The rate constants for quenching of triplet BPs by N and Q were also determined in acetonitrile by means of laser flash photolysis.The rate constants for N were not dependent on the triplet energies (ET) of BPs but dependent on electronic properties of the substituents on BPs.On the contrary, those for Q increased with decreasing ET of BPs and with increasing Hammet's ? constants of the substituents of BPs.Based on these observations an addition-elimination process is proposed for the N-->Q isomerization, and electron transfer process for the Q-->N isomerization.
- Arai, Tatsuo,Oguchi, Takahisa,Wakabayashi, Toshio,Tsuchia, Masahiro,Nishimura, Yoshinobu,et al.
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- Synthesis of Annelated Oxetans via Cycloaddition Reactions of Quadricyclane under Thermal and High Pressure Conditions
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Annelated oxetans are synthesized via thermal or pressure assisted cycloaddition of quadricyclane with the appropriate carbonyl bond activated by electron withdrawing groups; the new compounds are very stable and do not undergo the usual cycloreversion of four membered rings.
- Papadopoulos, Mihalis,Jost, Roland,Jenner, Gerard
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- Synthesis and gas-separation properties of metathesis poly(3-fluoro-3-pentafluoroethyl-4,4-bis(trifluoromethyl)tricyclonene-7)
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Metathesis polymerization of 3-fluoro-3-pentafluoroethyl-4,4-bis(trifluoromethyl)tricyclononene-7 (F-PTCN) and the properties of the resulting polymer, particularly gas permeability, have been studied. It has been found that F-PTCN exhibits high thermal stability. The gas separation parameters of the material (P(O2) = 60 Barrer, P(CO2) = 240 Barrer) are close to those of fluorinated polynorbornenes studied previously. The newly synthesized fluorinated metathesis polytricyclononene has a lower gas permeability than metathesis polytricyclononene bearing two Me3Si groups in the monomer unit, but it is significantly superior to the latter in gas separation selectivity for some gas pairs.
- Bermeshev,Starannikova,Sterlin,Tyutyunov,Tavtorkin,Yampolskii, Yu. P.,Finkelshtein, E. Sh.
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- PHOTOISOMERIZATION OF 7-SUBSTITUTED NORBORNADIENE-CYCLODEXTRIN INCLUSION COMPLEXES
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The photoisomerization of 7-substituted norbornadiene-cyclodextrin inclusion complexes, in which the substituents are t-butoxyl, acetoxyl, and hydroxyl groups, gave 7-substituted quadricyclene-cyclodextrin inclusion complexes.
- Yumoto, Takaari,Hayakawa, Kiyoshi,Kawase, Kaoru,Yamakita, Hiromi,Taoda, Hiroshi
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- Possibility of Photochemical Energy Storage in the Norbornadiene - Quadricyclane System. Part II
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Sensitization effect of an organic sensitizer propiophenone in the photoisomeric system norbornadiene - quadricyclane was investigated.Experimental data on the N - Q conversion for various concentrations of the sensitizer and irradiation times were given.Results confirmed a proposed kinetic model.
- Ristic, G. S.,Marinkovic, M. D.,Comor, J. J.,Vasic, V. M.,Ristic, M. S.,Nikolic, R. M.
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- Reactions of quadricyclane with fluorinated nitrogen-containing compounds. Synthesis of 3-aza-4-perfluoroalkyl-tricyclo[4.2.1.02,5]non-3,7- dienes
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The cycloaddition reactions of quadricyclane (1) and polyfluorinated imines and nitriles were studied. Both (CF3)2CNH and (CF 3)2CN(2-FC6H4) were found to have low reactivity towards 1, giving the corresponding [2 + 2 + 2] cycloadducts in a low yield. C2F5NCFCF3 however, reacts with 1 rapidly, giving a mixture of two isomeric cycloadducts in a high yield. Perfluoroalkyl nitriles RfCN (Rf = CF3, C 2F5, n-C3F7) were found to have surprisingly high reactivity to 1 producing exo-3-aza-4-(fluoroalkyl)- tricyclo[4.2.1.02,5]non-3,7-dienes in 56-81% yields at elevated temperature. Exo-3-aza-4-(perfluoroalkyl)-tricyclo[4.2.1.02,5]non-3, 7-dienes rapidly react with CF3Si(CH3)3 in the presence of CsF catalyst. The reaction results in addition of CF 3Si(CH3)3 across the CN bond of the azadienes with selective formation of only one stereoisomer of exo-3-aza-3- (trimethylsilyl)-4,4-bis(perfluoroalkyl)-tricyclo[4.2.1.02,5]non-7- enes. Silyl group in this compounds can be removed either by the action of tetrabutylammonium fluoride hydrate, leading to the formation of the corresponding amine after hydrolysis, or by reaction with HCl resulting in the formation of the corresponding amine hydrochloride. The reaction of quadricyclane with perfluoroazaalkenes and perfluorinated nitriles leads to high yield formation of the corresponding cycloadducts.
- Petrov, Viacheslav A.,Davidson, Frederic,Marshall, Will
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- Photosensitized Isomerization of Norbornadiene to Quadricyclane with (Arylphosphine)copper(I) Halides
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The (arylphosphine)copper(I) halides were studied as sensitizers in the photoisomerization side of a solar energy storage cycle based on the interconversion of norbornadiene (NBD) and quadricyclane (Q).The lowest electronic excited state of these compounds can be effective triplet energy sensitizers as evidenced by a maximum quantum yield of 1.0 with (MePh2P)3CuX.The efficiency of the (MePh2P)3CuX sensitizers is unprecedented compared to other reported inorganic complexes used as sensitizers for the NBD/Q system.The (MePh2P)3CuCl sensitizer has an intersystem crossing triplet yield of 1.0 with a triplet lifetime in benzene at room temperature of 3.3 μs.The triplet energy transfer rate constant with NBD is 8x107 M-1 s-1.While the L3CuX (L=Ph3P, MePh2P) species are the most efficient sensitizers in solution, dissociation of the ligand from the metal in dilute solution detracts from their otherwise attractive features.The much lower quantum efficiency observed for the (Ph3P)3CuX compared to the MePh2P sensitizer is attributed to this extensive ligand dissociation.The coordinately unsaturated (arylphosphine)copper(I) halides produced by ligand dissociation appear to have extremely short lifetimes while the free ligand undergoes photodecomposition.Ground-state complexation of NBD with the coordinately unsaturated (arylphosphine)copper(I) halides is shown to occur in the presence of a large excess of NBD.Photoexcitation of NBD-(MePh2P)CuCl (C1) and NBD-(MePh2P)2CuCl (C2) complexes can produce Q, but with quantum efficiencies less than one.
- Fife, Dennis J.,Moore, William M.,Morse, Karen W.
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- Bond-Coupled Electron Transfer Reactions: Photoisomerization of Norbornadiene to Quadricyclane
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In this paper, we report on the bond coupled electron transfer (BCET) isomerization reaction of norbornadiene (NB) to quadricyclane (Q). We have used several triplet sensitizers to examine electron and energy quenching by NB. In the case of acetophenone, energy transfer generates the detectable 3NB, which rearranges to give 3Q which relaxes to Q. Using chloranil, benzoquinone, and 2,5-dichlorobenzoquinone as triplet sensitizers, the triplet ion pairs are generated, but cannot access either 3NB or 3Q, and so the ion pair undergoes return electron transfer to the ground state. However, with 3,3',4,4'-benzophenonetetracarboxylic dianhydride as the triplet sensitizer, the triplet ion pair is generated, but can undergo BCET to 3Q efficiently, which then relaxes to Q. To our knowledge, this is the first example of an efficient electron-transfer mechanism to photoisomerize NB to Q without the intermediacy of 3NB. Consequently, in the valence isomerization of NB to Q, it is possible to directly access the NB-Q triplet surface by controlling the energy of the triplet ion pair photogenerated, and in effect, the quantum yield can be modulated.
- Cuppoletti, A.,Dinnocenzo, J. P.,Goodman, J. L.,Gould, I. R.
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- Energy storage material based on 2,5-norbornadiene derivative and preparation method thereof
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The invention discloses an energy storage material based on a 2,5-norbornadiene derivative and a preparation method thereof. An esterification method is used for preparing an ortho grafted bisazo benzene 2,5-norbornadiene derivative; two azobenzene groups are introduced at 2,5-norbornadiene in an ortho manner, so that norbornadiene is obviously subjected to Einstein shift; the photon yield is effectively improved. 2,5-norbornadiene and the azobenzene groups are combined, so that the heat storage energy density can be effectively improved; the storage energy is increased. The material has excellent optical performance and is hopeful to be applied in the fields of light and heat conversion and energy storage.
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Page/Page column 9
(2018/12/13)
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- A high-purity four cycloheptanes process for the continuous preparation of
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The invention discloses a continuous process for producing high-pure quadricyclane, in which “a reaction-rectification integral process” or “a reaction followed by rectification process” may be employed. The two processes both use a novel composite catalyst which is obtained by loading an organic photo-sensitizer on a solid photocatalyst, and the composite catalyst has a high activity and a good stability. In the reaction-rectification integral process, the composite catalyst is used by being blended with rectification fillers or covering the rectification fillers, so as to achieve the integration of the reaction and the rectification. In the reaction followed by rectification process, the composite catalyst and the rectification fillers are placed separately from each other. The two processes achieve a relatively short residence time of reactants, produce highly-pure quadricyclane, and reduce the formation of cokes.
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Paragraph 0039-0043
(2017/03/14)
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- REDOX-AUXILIARY CATALYSIS
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Disclosed herein is a method of activating a compound for a chemical reaction comprising functionalizing a compound with a redox auxiliary group and oxidizing the redox auxiliary group that is bonded to the compound, thereby activating the compound, wherein the activated compound undergoes a chemical reaction to form a product and the oxidation of the redox auxiliary group is reversible. Methods of making and using these materials are also disclosed.
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Paragraph 0007; 0102
(2015/05/26)
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- Solar driven uphill conversion of dicyclopentadiene to cyclopentadiene: An important synthon for energy systems and fine chemicals
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The retro Diels-Alder conversion of endo-dicyclopentadiene to cyclopentadiene (Cp)-which is thermodynamically uphill under ambient conditions (ΔG = +9.7 kcal mol-1; values based on computation at 273 K following CBS-QB3 methodology)-was carried out at 175-190 °C in neat state using solar energy. The reaction is thermodynamically favorable at elevated temperature. Considering heat release from the reverse reaction (ΔH = -23.4 kcal mol-1), the energy storage efficiency was computed to be ca. 5.5% with respect to the IR component in concentrated solar radiation. Solar energy was further utilized for preparation of a model 2,5-norbornadiene derivative (75% isolated yield) through the cycloaddition reaction of Cp with 4-phenylbut-3-yn-2-one at 150-185 °C. The norbornadiene-quadricyclane system has been proposed for solar energy storage, and its solar assisted synthesis would help reduce its carbon footprint over its life cycle. Norbornadiene synthesis using solar energy may also be of interest for greener processing of fuels derived from this compound. Cookson's cage ketone, which too has been proposed as an energy storage medium, was additionally synthesized from the Diels-Alder adduct of Cp and p-benzoquinone employing concentrated solar photo-thermochemical conditions. The reaction proceeded rapidly (15 min) and gave the desired product in 96% isolated yield. Besides the above applications, Cp is an important synthon in the preparation of fine chemicals.
- Dinda, Milan,Chakraborty, Supratim,Kanti Si, Mrinal,Samanta, Supravat,Ganguly, Bishwajit,Maiti, Subarna,Ghosh, Pushpito K.
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p. 54558 - 54564
(2015/02/05)
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- Synthesis and photochemical properties of imide and amide models containing pentamethylated norbornadiene residues
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Four pentamethylated norbardiene (NBD) models containing imide, bis-imide and diamides were synthesized in the first step of this work with a good yield and characterized by IR, 1HNMR and 13CNMR spectroscopies. These models were used for study, by UV-Visible spectrophotometry, of the photochemical isomerisation under solar radiations of NBD residues, which they contain to quadricyclane (QC). Acquired results show, for all these models, that more than 70 % of NBD are transformed into QC after only 30 minutes of solar radiations and following a first order rate.
- Oueslati, Ahmed,Ben Romdhane, Hatem,Mercier, Régis,Chaabouni, Refaat M.
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scheme or table
p. 1406 - 1415
(2011/11/06)
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- Fluorinated monomers, fluorinated polymers having polycyclic groups with fused 4-membered heterocyclic rings, useful as photoresists, and processes for microlithography
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The present invention provides novel fluorine-containing copolymers which comprise at least one fluorinated olefin, at least one polycyclic ethylenically unsaturated monomer with a fused 4-membered heterocyclic ring and, optionally, other components. The copolymers are useful for photoimaging compositions and, in particular, photoresist compositions (positive-working and/or negative-working) for imaging in the production of semiconductor devices. The copolymers are especially useful in photoresist compositions having high UV transparency (particularly at short wavelengths, e.g., 157 nm) which are useful as base resins in resists and potentially in many other applications.
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Page/Page column 9
(2008/06/13)
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- Process of quadricyclane production
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The present invention relates to a process for efficiently producing quadricyclane by the conversion of norbornadiene. A sensitizer, such as a substituted diaminobenzophenone having a solubility in norbornadiene greater than that of Michler's Ketone, may be added to the norbornadiene to form a solution, wherein the sensitizer decreases the induction period at the beginning of the reaction, increases the photon or quantum efficiency of conversion of norbornadiene to quadricyclane, and increases the rate of conversion at the end of the reaction. The solution may be irradiated with light from a metal halide-doped mercury arc lamp and filtered through a sharp cut-off filter to render photochemical transformation of norbornadiene to quadricyclane more efficient than when other light sources are utilized. Furthermore, the addition of a base to the solution tends to result in the formation of fewer by-products in the transformation reaction.
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- Thermal Decomposition of a Series of 1,2-Diazetines
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A homologous series of tricyclic diazetines (6a-c), differing by the number of methylene groups in the saturated bridges of the fused carbon bicycles, was synthesized. The ΔH? of decomposition for each of the diazetines to afford N2 and the corresponding alkene was determined experimentally: 6a, 31.7; 6b, 39.3; 6c, 38.8 kcal/mol. The ground-state strain energy of each diazetine was estimated utilizing computationally obtained ΔHf's for each of the experimentally investigated diazetines as well as several other diazetines whose ΔH?'s had been previously reported in the literature. The sum of the ground-state strain energies and ΔH?'s of decomposition for all of the diazetines was nearly constant, with an average value of 59 kcal/mol, suggesting that all of the diazetines decompose via the same mechanism. Generally, the higher the ground-state strain energy of the diazetine, the less the ΔH? for decomposition. The decomposition transition states for 6a-c and 7 were modeled computationally at the RB3LYP/6-311+G(3df,2p)//UB3LYP/6-31+G(d,p) level. The agreement of the experimentally determined ΔH? values with transition-state energies obtained computationally supports the reaction mechanism originally proposed by Yamabe that the elimination process occurs by an unsymmetrical, yet concerted, transition state with strong biradical character.
- Breton, Gary W.,Shugart, John H.
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p. 8643 - 8649
(2007/10/03)
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- Process of driving a non-polymerization solution-phase photochemical transformation
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The present invention relates to a process for driving a non-polymerization solution-phase photochemical transformation. A sensitizer, such as a substituted diaminobenzophenone having a solubility in norbornadiene greater than that of Michler's Ketone, may be added to norbornadiene to form a solution, wherein the sensitizer decreases the induction period at the beginning of the reaction, increases the photon or quantum efficiency of conversion of norbornadiene to quadricyclane, and increases the rate of conversion at the end of the reaction. If the solution is irradiated with light from a metal halide-doped mercury arc lamp to photochemically transform the norbornadiene to quadricyclane, the conversion is more efficient than when other light sources are utilized. Furthermore, the addition of triethylamine to the solution tends to result in the formation of fewer by-products in the transformation reaction.
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(2008/06/13)
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- Experiments towards the formation of 1,6-dehydroquadricyclane and density functional calculations on this and related molecules
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1,6-Dibromoquadricyclane (6) was obtained from norbornadiene (11) by hydroboration, oxidation of the diol 12 to the diketone 14 and its conversion into 2,6-dibromonorbornadiene (20) using tribromodioxaphosphole 16b followed by treatment of the mixture 17/18 with potassium tert-butoxide in DMSO and photocyclization of 20. Reaction of 6 with tBuLi (2 equiv.) led to the formation of 1-bromo-6-lithioquadricyclane 7, the NMR spectra of which were observed up to 0°C. 7 did not lose LiBr to give 4, but could be trapped with H2O and chlorotrimethylsilane to give 21e (53%) and 21f (64%). Reaction of 6 with fBuLi (> 4 equiv.) gave rise to 1,6-dilithioquadricyclane (21c), whose NMR spectra could also be recorded. 21c was converted into the corresponding 1,6-disubstituted quadricyclanes with D2O (87%), chlorotrimethylsilane (92%), dimethyl sulfate (55%), methyl chloroformate (45%), iodine monochloride (62%), and p-toluenesulfonyl chloride (48%). - Density functional calculations using the B3LYP/6-31G* level of theory showed that 1,6-dehydroquadricyclane (4) is a local energy minimum in its singlet electronic state. 4 contains a unique structure with 4 condensed cyclopropane units. The parent hydrocarbons 27 and 28, hitherto unknown, are also local energy minima in their singlet electronic states.
- Glueck-Walther, Susanne,Jarosch, Oliver,Szeimies, Guenter
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p. 493 - 500
(2007/10/03)
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- Rh(III)-photosensitized interconversion of norbornadiene and quadricyclane
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The utility of two Rh(III) diimine complexes, Rh(phen)33+ and Rh(phi)2(phen)3+ (phen = 1,10-phenanthroline, phi = 9,10-phenanthrenequinone diimine), as sensitizers for the interconversion of norbornadiene (N) and quadricyclane (Q) has been investigated using steady-state photochemical and laser flash photolysis (LFP) techniques. Irradiation of acetonitrile solutions of Rh(phen)33+ and N causes slow conversion to Q. The reaction is reversible; irradiation of Rh(phen)33+ in the presence of Q leads to N. Irradiation of acetonitrile solutions of Rh(phi)2(phen)3+ and Q yields N. However, this reaction is irreversible; irradiation of the Rh-(III) complex in the presence of N fails to afford Q. Irradiation of methanol solutions of either Rh(III) complex in the presence of N or Q affords minor amounts of two methanol-C7 adducts but fails to quench the N-Q interconversion reaction. The results are consistent with N-Q interconversion via an exciplex intermediate. The Rh(III)-sensitized deazatization of two cyclic azoalkane derivatives (Azo-N, Azo-Q) of N and Q was also investigated. Deazatization was achieved by Rh(phen)33+ but not Rh(phi)2(phen)3+ sensitization. The results are consistent with a mechanism involving triplet energy transfer, but the involvement of exciplex intermediates cannot be ruled out. Bimolecular rate constants for quenching of the Rh(III) excited states by N, Q, Azo-N, and Azo-Q were determined by LFP.
- Sluggett, Gregory W.,Turro, Nicholas J.,Roth, Heinz D.
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p. 8834 - 8838
(2007/10/03)
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- Reactivity and thermochemistry of quadricyclane in the gas phase
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The gas-phase acidity of quadricyclane C7H8 has been determined using a flowing after-glow selected ion flow tube at room temperature. Measurements of forward and reserve rate constants for the proton transfer reaction B- + C7H8 ? C7H7- + BH where BH = NH3, CH3NH2 and C6H6 give ΔacidG300(C7H8) = 394.7±0.8 kcal/mol and ΔacidH300(C7H8) = 403.0±1.1 kcal/mol. Combining this value with the electron affinity, 0.868±0.006 eV, of the quadricyclyl radical, gives 109.4±1.3 kcal/mol for the C-H bond dissociation energy of quadricyclane at Cl. Reactions of quadricyclane ion with various reagents have been studied, and branching ratios of product channels have been determined. These results along with ab initio calculations and a companion photoelectron spectroscopy study, indicate that there are two isomers of quadricyclane ion which have similar energies. The gas-phase acidity of quadricyclane, C7H8, has been determined using a flowing afterglow-selected ion flow tube at room temperature. Measurements of forward and reverse rate constants for the proton transfer reactions B- + C7H8 ? C7H7- + BH where BH = NH3, CH3NH2, and C6H6 give Δ(acid)G300(C7H8) = 394.7 ± 0.8 kcal/mol and Δ(acid)H300(C7H8) = 403.0 ± 1.1 kcal/mol. Combining this value with the electron affinity, 0.868 ± 0.006 eV, of the quadricyclyl radical, gives 109.4 ± 1.3 kcal/mol for the C-H bond dissociation energy of quadricyclane at C1. Reactions of quadricyclanide ion with various reagents have been studied, and branching ratios of product channels have been determined. These results, along with ab initio calculations and a companion photoelectron spectroscopy study, indicate that there are two isomers of quadricyclanide ion which have similar energies.
- Lee, Hack Sung,DePuy, Charles H.,Bierbaum, Veronica M.
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p. 5068 - 5073
(2007/10/03)
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- Electron transfer induced deazatization of cyclic Azo derivatives of quadricyclane and norbornadiene
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The photosensitized oxidation of two cyclic azoalkane derivatives (Azo-Q, Azo-N) of quadricyclane (Q) and norbornadiene (N) has been investigated using steady-state and laser flash photolysis techniques as well as chemically induced dynamic nuclear polarization (CIDNP). Irradiation of acetonitrile solutions of 9,10-dicyanoanthracene (DCA), 2,6,9,10-tetracyanoanthracene (TCA), or chloranil (Chl) in the presence of Azo-Q results in rapid and efficient deazatization to afford N. Similar irradiation of DCA, TCA, and Chl in the presence of Azo-N yields N and Q. CIDNP experiments reveal that polarized N is formed as a cage product in the Chl sensitized photolysis of Azo-Q while polarized N and Q are both formed as cage products from Azo-N. The results are consistent with competitive fragmentation of Azo-N?+ to N?+ and Q?+, and selective deazatization of Azo-Q?+ to N?+. Irradiation of 1-cyanonaphthalene in the presence of Azo-Q or Azo-N affords Q and/or N in chemical yields similar to those obtained from direct and naphthalene sensitized irradiations, indicative of singlet energy transfer quenching. Bimolecular rate constants for quenching by Azo-N and Azo-Q were determined by steady-state fluorescence methods for singlet sensitizers, or by laser flash photolysis (LFP) for 3Chl*.
- Sluggett, Gregory W.,Turro, Nicholas J.,Roth, Heinz D.
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p. 9982 - 9989
(2007/10/03)
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- Electron Transfer Photoisomerization of Norbornadiene to Quadricyclane Cosensitized by Dibenzoylmethanatoboron Difluoride and Aromatic Hydrocarbons
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Chemically induced dynamic nuclear polarization (CIDNP) was used to study the valence isomerization of norbornadiene (NBD) to quadricyclane (QC) sensitized by dibenzoylmethanatoboron difluoride (DBMBF2).While DBMBF2 readily sensitized QC to NBD via an electron transfer mechanism, it did not promote the reverse isomerization.In contrast, in the presence of an aromatic co-sensitizer, such as toluene, ethylbenzene, biphenyl or durene, DBMBF2 sensitized NBD isomerization to QC.The novel result is rationalized by invoking a photoinduced electron transfer mechanism, involving triplexes, as the key intermediate which facilitates triplet recombination of the ion radical pair.
- Liu, Zhong-Li,Zhang, Mao-Xi,Yang, Li,Liu, You-Cheng,Chow, Yuan L.,Johansson, Carl I.
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p. 585 - 590
(2007/10/02)
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- Photochemistry of "salted" quadricyclane and norbornadiene: Alkali halide color centers as catalysts
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Quadrtcyclane "salted" in CsI or KBr or in with is rapidly into norbornadiene under condition that induce color centre formation in the haide: rapid-growth vapor or UV or X-ray irradiation. The reaction proceeds at where the H centers are mobile. At lower temperatures, UV irradiation of norbornadiene converts it into quadricyclane in the fashion.
- Kirkor, Ewa S.,Maloney, Vincent M.,Michl, Josef
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p. 148 - 151
(2007/10/02)
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- Reactivity and selectivity in host-guest inclusion compounds
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The reaction processes which occur in the solid state are thoroughly investigated for the specific case of host-guest inclusion compounds with particular attention to the isomerization of cis-trans-olefines, to valence isomerization of norbornadiene and to the isomerization vs. disproportionation of xylenes.The steric constraints which are particularly important in reactions inside the cavities ot these compounds are discussed and shown to be a decisive factor in determining the reaction path as well as the yields of isomerization products.
- Guarino, A.,Possagno, E.,Bassanelli, R.
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p. 253 - 258
(2007/10/02)
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- Photochemical conversion of norbornadiene into quadricyclane in the presence of acridinone-type sensitizers
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In this study, a series of acridinones and benzo-fused acridinones have been used for the first time as efficient photosensitizers for the norbornadiene-quadricyclane isomerization by near UV and visible iradiation.Their triplet energies (240-280 kJ.Mol-1) are well below the value of 290 kJ.Mol-1 which is generally assumed for norbornadiene.A mechanism is postulated involving an exciplex between sensitizer and norbornadiene.Limiting quantum yields of 0.5 and higher have been determined for this valence isomerization extrapolated to infinite norbornadiene concentration.Exciplex formation is supported by measurements of the rate of constant k2 for quenching of excited sensitizer by norbornadiene, yielding values which are much smaller than the diffusion-controlled quenching constant.
- Tinnemans, A. H. A.,Ouden, B. den,Bos, H. J. T.,Mackor, A.
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p. 109 - 116
(2007/10/02)
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- Stereochemistry of the Bicyclopentane Ringopening; Thermolysis of Tricyclo2,4>heptane Derivatives
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Thermolysis of the anti-tricyclic compounds 6, 22 and 34 proceeds preferentially by concerted 2s+?2a>-reactions and leads to cis,trans-olefines 8, 24 and 37.The rearrangement of the syn-isomers on the other hand seems to be a nonconcerted reaction yielding the diradicals 15, 27 and 36.
- Roth, Wolfgang R.,Klaerner, Frank-Gerit,Grimme, Wolfram,Koeser, Hans G.,Busch, Ralf,et al.
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p. 2717 - 2737
(2007/10/02)
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- Photoconversion of norbornadiene to quadricyclene in the presence of a copper(I) carbonyl compound
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A detailed study of the thermal and photochemical behavior of Cu[HB(pz)3](CO) [HB(pz)3- is hydrotris(1-pyrazolyl)borate] in the presence of norbornadiene (NBD) is reported. In solution NBD displaces CO from the coordination sphere of copper to produce a new complex formulated as Cu[HB(pz)3](NBD). This ground-state process is readily discernible by a shift in the absorption spectrum of the system to longer wavelengths. Irradiation of the complex with 313-nm light induces the valence isomerization of norbornadiene to quadricyclene with high quantum efficiency. The occurrence of this pathway is explicable in terms of the bonding changes that result from populating an excited state possessing Cu-NBD charge-transfer character.
- Sterling, Rosstain F.,Kutal, Charles
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p. 1502 - 1505
(2008/10/08)
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