RADIATION-INDUCED CHANGES IN THE UNSATURATION OF POLYISOPRENE

1965 ◽  
Vol 43 (10) ◽  
pp. 2772-2785 ◽  
Author(s):  
Morton. A. Golub ◽  
Jeanne. Danon
Keyword(s):  
Energy Transfer ◽  
Solid State ◽  
Benzene Solution ◽  
Chain Process ◽  
Energy Transfer Mechanism ◽  
Carbonium Ions ◽  
Intermolecular Energy ◽  
Radiation Induced ◽  
A Chain ◽  
Induced Changes

Polyisoprene in the solid state and in benzene solution undergoes radiation-induced cis-trans isomerization and loss of unsaturation. Starting with various cis or trans polymers, the isomerization approaches an equilibrium in which the cis/trans ratio is around 50/50 for polyisoprenes irradiated in solution or in the solid state. The G(isom.) values for either cis → trans or trans → cis isomerization, i.e., the number of cis (or trans) units isomerized initially per 100 eV absorbed by both polymer and solvent, in 1% solution, and by polymer alone, in the solid state, are about 1.0 and 10, respectively. The energy transfer mechanism proposed previously for polybutadiene and squalene isomerization is assumed to hold for polyisoprene as well. The loss of unsaturation in films irradiated with electrons under nitrogen is twice as rapid as in films γ-irradiated in vacuo, the G(-d.b.) (d.b. = double bond) values being 13.4 and 6.7, respectively. Correspondingly, G(-d.b.) for a γ-irradiated solution is 27, calculated in terms of energy absorbed directly by the polymer; intermolecular energy transfer is again indicated, although phenylation may also contribute to the loss of double bonds in solution. The large drop in unsaturation in solution and in the solid state is attributed to a chain process involving cyclization and some cross-linking, with the participation of both free radicals and carbonium ions. Work with polyisoprene-3-d confirmed the importance of isomerization and loss of unsaturation and gave an activation energy of 1.1 kcal/mole for the latter reaction.

Un exemple d'isomérisation radicalaire en chaînes: la photoinduction de l'isomérisation cis–trans de la pentène-3 one-2

1977 ◽  
Vol 55 (22) ◽  
pp. 3915-3926 ◽  
Author(s):  
Armel Rioual ◽  
André Deflandre ◽  
Jacques Lemaire
Keyword(s):  
Energy Transfer ◽  
Quantum Yields ◽  
Unsaturated Ketone ◽  
Chain Process ◽  
Triplet Energy ◽  
Low Concentrations ◽  
Energy Transfers ◽  
Donor And Acceptor ◽  
A Chain ◽  
Triplet Energy Transfer

Mechanisms of the photosensitized cis–trans photoisomerization of 3-penten-2-one which do not imply only classical triplet–triplet energy transfer are proposed; they are based upon measurements of the variations of initial quantum yields of isomerization with the initial donor and acceptor concentrations, the wavelength of excitation, and the nature of the donor and of the solvent. Carbonyl donors (acetophenone, benzophenone, acetone) induce a radical isomerization by a chain process in reducing solvents; the example of acetophenone is specially interesting. In solvents in which the donor is not photoreduced (as benzene or CCl4) classical triplet–triplet energy transfers occur. Sensitization with aromatic donors (benzene, mesitylene) proceeds through triplet–triplet energy transfer at low concentrations of the acceptor. At higher concentrations of acceptor, an exciplex is formed between the ketone and the aromatic in its singlet excited state; this exciplex is deactivated by dissociation and by causing the isomerization of the α,β-unsaturated ketone.

scholarly journals Photophysical properties and energy transfer mechanism of a praseodymium compound with a two-dimensional layer

2020 ◽  
Vol 44 (5-6) ◽  
pp. 343-348
Author(s):  
Wen-Tong Chen
Keyword(s):  
Energy Transfer ◽  
Solid State ◽  
Hydrothermal Reaction ◽  
Photophysical Properties ◽  
Transfer Mechanism ◽  
Energy Transfer Mechanism ◽  
Two Dimensional ◽  
Monoclinic System ◽  
Reflectance Measurement ◽  
Praseodymium Complex

A hydrothermal reaction results in the formation of a novel [Pr2(2,5-PA)2(2,5-HPA)2(H2O)4] n·2 nH2O complex (2,5-H2PA = 2,5-pyridinedicarboxylic acid). The complex is structurally characterized by single-crystal X-ray diffraction and crystallizes in the space group P21 of the monoclinic system with two formula units in one cell. This praseodymium complex is characterized by a two-dimensional layered structure. A solid-state photoluminescence experiment reveals that the praseodymium complex shows an emission in the red region. The complex has Commission Internationale de I’Éclairage chromaticity coordinates of 0.5495 and 0.4492. The photoluminescence emission bands could be assigned to the characteristic emission of the 4 f electron intrashell transition of the 3 P0 → 3 H5, 1 D2 → 3 H4, 3 P0 → 3 H6, 3 P0 → 3 F2, and 3 P1 → 3 F3 of the Pr3+ ions. The energy transfer mechanism is explained by the energy level diagrams of the praseodymium ions and the 2,5-H2PA ligand. A solid-state diffuse reflectance measurement shows that the complex possesses a wide optical band gap of 3.48 eV.

scholarly journals Luminescence properties and energy transfer in Tb3+ and Eu3+ co-doped Ba2P2O7 phosphors

RSC Advances ◽  
2017 ◽  
Vol 7 (25) ◽  
pp. 15222-15227 ◽  
Author(s):  
Baoxing Wang ◽  
Qiang Ren ◽  
Ou Hai ◽  
Xiulan Wu
Keyword(s):  
Energy Transfer ◽  
High Temperature ◽  
Solid State ◽  
Solid State Reaction ◽  
Solid State Reaction Method ◽  
Luminescence Properties ◽  
Energy Transfer Mechanism ◽  
Reaction Method ◽  
Air Atmosphere ◽  
Co Doped

The Ba2P2O7:Tb3+, Eu3+ phosphors were synthesized by a high temperature solid-state reaction method in air atmosphere and their crystal structures, lifetime, luminescence properties, and energy transfer mechanism were investigated in detail.

Solid-State Photodecarbonylation of Diphenylcyclopropenone:  A Quantum Chain Process Made Possible by Ultrafast Energy Transfer

2008 ◽  
Vol 130 (4) ◽  
pp. 1140-1141 ◽  
Author(s):  
Gregory Kuzmanich ◽  
Arunkumar Natarajan ◽  
Khin K. Chin ◽  
Marcel Veerman ◽  
Christopher J. Mortko ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Solid State ◽  
Chain Process ◽  
Quantum Chain

scholarly journals Люминофор ближнего и коротковолнового ИК-диапазона на основе ниобата литий-лантана со структурой кубического граната

2019 ◽  
Vol 61 (5) ◽  
pp. 967
Author(s):  
Я.В. Бакланова ◽  
О.А. Липина ◽  
Л.Г. Максимова ◽  
И.В. Бакланова ◽  
А.Ю. Чуфаров ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Solid State ◽  
Solid Solutions ◽  
Short Wave ◽  
Energy Transfer Mechanism ◽  
Active Centers ◽  
Solid State Method ◽  
Near Ir ◽  
State Method ◽  
High Luminescence Intensity

AbstractCubic garnets activated by neodymium and holmium, Li_6CaLa_2Nb_2O_12:Nd^3+,Ho^3+, were obtained by solid-state method. The main regularities of changes in the luminescence properties of Li_6C-aLa_2Nb_2O_12:Nd^3+,Ho^3+ solid solutions in the visible, near-IR, and short-wave IR ranges under 808 nm laser diode radiation are determined. The energy transfer mechanism between active centers, involving the participation of Nd^3+ ions as sensitizers for the luminescence of Ho^3+ ions, is proposed. Low phonon energy, high luminescence intensity in the range of 2.0–3.0 μm, and weak up-conversion luminescence in the region of 450–780 nm make it possible to consider the cubic lithium–lanthanum niobates Li_6CaLa_2Nb_2O_12:Nd^3+,Ho^3+ as promising phosphors of the short-wave IR range.

scholarly journals Preparation and characterization of a gadolinium compound with high thermal stability

2021 ◽  
Vol 34 (3) ◽  
pp. 479-488 ◽  
Author(s):  
W. T. Chen
Keyword(s):  
Thermal Stability ◽  
Energy Transfer ◽  
Solid State ◽  
Three Dimensional ◽  
Blue Emission ◽  
Energy Transfer Mechanism ◽  
Blue Emission Band ◽  
Characteristic Emission ◽  
Pyridinedicarboxylic Acid ◽  
Cie Chromaticity

A new lanthanide compound [Gd(2,5-HPA)(2,5-PA)]n (1; 2,5-H2PA = 2,5-pyridinedicarboxylic acid) was obtained through hydrothermal reactions and structurally characterized by single-crystal X-ray diffraction. It possesses a three-dimensional (3-D) framework structure. Solid-state photoluminescence experiment revealed that it shows dark blue emission band, which can be assigned to the characteristic emission of the 4f electron intrashell transition of 6P7/2 → 8S7/2 (Gd3+). The energy transfer mechanism was explained by an energy level diagram of the gadolinium ion and 2,5-pyridinedicarboxylic acid ligand. It displayed remarkable CIE chromaticity coordinates of 0.1346 and 0.0678. The solid-state UV/Vis diffuse reflectance spectra unveiled that it possesses a wide optical band gap of 3.52 eV. Thermogravimetry (TG) measurements revealed that this compound is highly thermal stable up to around 500 °C.                     KEY WORDS: CIE, Energy transfer, Lanthanide, Photoluminescence, Thermal stability   Bull. Chem. Soc. Ethiop. 2020, 34(3), 479-488. DOI: https://dx.doi.org/10.4314/bcse.v34i3.5

Untersuchung der cis-trans-Isomerie des WITTIGschen Kohlenwasserstoffs / Investigation of the cis-trans-Isomerism of the WITTIG Hydrocarbon

1976 ◽  
Vol 31 (6) ◽  
pp. 810-815 ◽  
Author(s):  
Rolf Sartorius ◽  
Reinhard Schmidt ◽  
Hartwig Kelm ◽  
Hans-Dieter Brauer
Keyword(s):  
Energy Transfer ◽  
Solid State ◽  
Fluorescence Spectroscopy ◽  
Trans Isomer ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Exciting Radiation ◽  
Energy Transfer Mechanism ◽  
Enthalpy Difference ◽  
Cis Isomer

The cis-trans-isomerism of the WITTIG hydrocarbon was investigated in solid state and solution by means of fluorescence spectroscopy. The fluorescence behavior of both isomers in 2-methyltetrahydrofurane was determined as a function of concentration, temperature, and wavelength of exciting radiation. Furthermore, irradiation experiments were undertaken with light of various wavelengths.The results obtained are in agreement with the assumption that the WITTIG hydrocarbon behaves with regard to the cis-trans-isomerism like a 1,3-butadien derivative, i.e. a thermal but no photochemical cis-trans-isomerisation can be detected. The enthalpy difference between the two isomers was estimated to ΔΗ = 250 ± 50 cal/mole. It could be shown that the fluorescence of the cis-isomer is quenched by the trans-isomer. This quenching occurs probably according to the resonance energy transfer mechanism.

Synthetic application of α-hydroxydiazene systems. II. Uncatalyzed and phenol catalyzed radical chain hydro-tert-butylation of unsaturated compounds with tert-butylazodiphenylcarbinol

1976 ◽  
Vol 54 (9) ◽  
pp. 1345-1348 ◽  
Author(s):  
Dominic W. K. Yeung ◽  
John Warkentin
Keyword(s):  
Benzene Solution ◽  
Chain Process ◽  
The Novel ◽  
Radical Chain ◽  
Tert Butyl ◽  
Radical Adduct ◽  
Butyl Radical ◽  
A Chain ◽  
Radical Traps ◽  
Synthetic Application

tert-Butylazodiphenylcarbinol 1 decomposes in benzene solution by a chain mechanism involving tert-butyl radicals. Many olefinic compounds and azobenzene act as radical traps and are hydro-tert-butylated by 1. The regiochemistry of hydro-tert-butylation of unsymmetric alkenes is that expected for a mechanism which involves addition of tert-butyl radical so as to form the most stable radical adduct, which subsequently abstracts hydrogen from 1.In some cases phenol acts as a catalyst for the hydroalkylation process. The novel catalytic effect of phenol in a radical chain process is attributed to the favourable thermochemistry for induced, concerted decomposition of 1 by radical attack at hydroxyl hydrogen.

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