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J.b. Moffat - One of the best experts on this subject based on the ideXlab platform.
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Isomerization of 1-butene on supported and unsupported Metal-Oxygen Cluster compounds (heteropoly oxometalates)
Catalysis Letters, 1996Co-Authors: S. Gao, J.b. MoffatAbstract:On 12-tungstophosphoric acid (HPW) supported on silica, 1-butene is isomerized to cis- and trans-2-butene at 100°C and higher while a temperature of 150°C is required to form isobutene. While the conversion remains at 80–90% regardless of the loading of HPW on the support and the reaction temperature, the selectivity to isobutene reaches a maximum of 33% at a loading of 23% HPW/SiO_2 and 300–350°C. Small quantities of C_ n ( n = 3,..., 8) species are also formed. These results together with those from ammonia poisoning, temperature-programmed desorption of ammonia,^1H MAS NMR and infrared spectroscopy show that HPW/SiO_2 possesses sites of strength as high as or higher than those on HZSM-5, that such sites are required for the skeletal isomerization process and that both mono- and bimolecular processes are occurring on the catalyst. The absence of dependence of conversion of 1-butene and selectivities to cis- and trans-2-butene on loading and reaction temperature can best be rationalized on the basis of a rapid attainment of an equilibrium between the aforementioned three species and sec-butyl carbenium ions from which pool the energy barrier to the primary butyl carbenium and hence to isobutene is surmounted, given appropriate conditions.
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Microporous Metal—Oxygen Cluster Compounds (Heteropoly Oxometalates): Synthetic Variables, Nature and Source of the Porosity, Catalytic Applications, and Shape Selectivity
Advanced Catalysts and Nanostructured Materials, 1996Co-Authors: J.l. Bonardet, G.b. Mcgarvey, K. Carr, J. Fraissard, J. B. Mcmonagle, M. Seay, J.b. MoffatAbstract:Publisher Summary Heteropoly oxometalates (also known as Metal-Oxygen Cluster compounds, MOCC) have been known for more than 150 years. Although another form of oxygen polyanion exists, namely the isopolyanions the heteropoly ions are those that contain two different elements in addition to oxygen. While many possible structures are known for the heteropoly anions, that elucidated by Keggin has been more commonly studied for its catalytic and surface properties. A number of isomers of the Keggin structure are known; of these the α form appears to be the most stable and as a consequence catalytic investigations have generally focused on this isomer. The Keggin structure has a central atom (X) bonded to four oxygen atoms arranged tetrahedrally. Most of the surface and catalytic studies have employed P or Si as the central atom although, as noted earlier, many possibilities exist. The selection of P or Si as the central atom undoubtedly relates to factors of thermal stability, ease of preparation, and cost. The central XO4 tetrahedron is surrounded by 12 octahedra with a peripheral metal atom (M) at each of their approximate centers and oxygen atoms at their vertices. For catalytic purposes the more common peripheral metal atoms are W, Mo, and V. The octahedra share oxygen atoms with each other and with the central atom. The 12 octahedra are arranged in four groups of three edge-shared octahedra, M 3 0 13 , which are linked by shared corners to each other and to the central XO 4 tetrahedron. There are two types of bridging oxygen atoms, those connecting the central atom to the peripheral metal atoms and those joining each of the peripheral metal atoms.
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Metal−Oxygen Cluster Compounds (Heteropoly Oxometalates) of 1B and 3B Monovalent Cations and Their Micropore Structure
Langmuir, 1996Co-Authors: M. A. Parent, J.b. MoffatAbstract:Silver and thallium, representatives from the periodic table's groups 1B and 3B, respectively, were employed as cations to synthesize stoichiometric and nonstoichiometric salts of 12-tungstophosphoric, 12-molybdophosphoric, and 12-tungstosilicic acids. All the solids, except silver 12-molybdophosphate, have high surface areas and microporous structures, as shown from the analysis of nitrogen adsorption−desorption isotherms obtained at 77 °K. Powder X-ray diffraction, temperature-programmed desorption, infrared spectroscopy, and 1H MAS NMR spectroscopy are employed to characterize the synthesized materials.
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Microporous Metal-Oxygen Cluster compounds (heteropoly oxometalates) : synthetic variables, nature and the source of the porosity and catalytic applications
Preprints-American Chemical Society Division of Petroleum Chemistry, 1995Co-Authors: J.b. Moffat, G.b. Mcgarvey, J.l. Bonardet, K. Carr, J. Fraissard, J. B. Mcmonagle, M. SeayAbstract:During the last two decades interest in solids containing pore structures has risen markedly. In particular catalysts containing micropores have been shown to posses both interesting and avantageous properties. The solids under discussion in the present report have both similarities and dissimilarities to porous zeolites.
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MICROPOROUS-MESOPOROUS Metal-Oxygen Cluster COMPOUNDS: ION EXCHANGE, STRUCTURE RETENTION AND THE OXIDATIVE DEHYDROGENATION OF ISOBUTYRIC ACID
Multifunctional Mesoporous Inorganic Solids, 1993Co-Authors: G.b. Mcgarvey, J.b. MoffatAbstract:Metal-Oxygen Cluster compounds can be prepared with microporous-mesoporous structures by precipitation of certain of their monovalent cation salts from aqueous solution. Exchange of the cations of these salts can be achieved, although the exchange is not complete and is dependent upon the relative sizes of the entering and leaving cations. Measurements of surface areas, pore size distributions and lattice parameters, before and after cation exchange, show that the microporous-mesoporous structures are semiquantitatively retained, although not surprisingly shifted as a result of the change in size of the cation. The catalytic properties of the exchanged microporous-mesoporous Metal-Oxygen Cluster compounds, as reflected in the conversion of isobutyric acid and selectivity to the various products, show a dependence on the nature and concentration of the cations as well as the expected relationship to the elemental composition of the anions.
John B. Moffat - One of the best experts on this subject based on the ideXlab platform.
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metal oxygen Clusters the surface and catalytic properties of heteropoly oxometalates
2001Co-Authors: John B. MoffatAbstract:1: A Brief Look at the Early History of Heteropoly Oxometalates. I. History. II. References. 2: Synthesis. I. Introduction. II. The 12-heteropoly acids. III. Various Syntheses. IV. References. 3: Characterization. I. Spectroscopy. II. Electrochemical Methods. III. Elemental Analysis. IV. Other Techniques. V. References. Chapter 4: Structure and Bulk Properties. I. Anions. II. Cations and Crystallographic Structure. III. Langmuir Films. IV. References. 5: Stability. I. Thermal Stability. II. pH Stability. III. Regeneration in the Presence of Water. IV. References. 6: Supported Heteropoly Acids and Their Derivatives. I. Supports. II. Formation of Heteropoly Acids from Oxides Supported on Silica. III. References. 7: Microporosity. I. Introduction. II. Microporosity of Salts prepared from the Monovalent Cations of the Group 1 Alkali Metals and Ammonium and Related Cations. III: A. Microporosity of the Salts Prepared from the Monovalent Cations of the Groups 11 and 13 Elements. B. Stoichiometric and Nonstoichiometric Salts of Groups 11 and 13 and Their Morphological Properties. IV. Pore Structures from 129Xe NMR. V. Sorption and Diffusion in Metal-Oxygen Cluster Compounds. VI: A. Cation Exchange and Microporosity. B. Crystal Structure and Morphology Retention on Ion Exchange. VII. Argon Adsorption. VIII.Divalent Salts. IX. Reactions on the Microporous Salts and Shape Selectivity. X. References. 8: The Two Functions: Acidity and Oxidation-Reduction. I. Acidity. II. Oxidation-Reduction. III. References. 9: Acid-Catalyzed Processes. I. Methanol Conversion to Hydrocarbons. II. Ethanol. III. Propene. IV. Propanol. V. Butane. VI. Butene. VII. Isobutane. VIII. Isobutene. IX. Butanol. X. Alkylation Processes. XI. Friedel-Crafts Reactions. XII. C5-C8 Alkanes. XIII. C6-C8 Alkenes. XIV. Ring-Expansion of Methylcyclopentane and Ring-Contraction of Cyclohexane. XV. References. 10: Oxidation Processes. I. A. Methane. B. The Effect of Gas Phase Additives in the Conversion of Methane on Heteropoly Oxometalates. II. Ethane. III. Propane. IV. Butane. V. Isobutane. VI. Methacrolein. VII. Isobutyric Acid. VIII. Pentane. IX. Butadiene. X. 1-Butene. XI. Cyclohexane. XII. Ammoxidation. XIII. References. 11: Environmentally-Related Processes. I. Conversion of Nitrogen Oxides. II. Hydrodesulphurization. III.Polymerization. IV. References.
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The interaction of nitrogen oxides with Metal-Oxygen Cluster compounds (heteropoly oxometalates)
Journal of Molecular Catalysis A: Chemical, 1996Co-Authors: R Bélanger, John B. MoffatAbstract:Abstract Nitrogen dioxide is sorbed by the solid heteropoly acids, the first sorbates producing HNO3 while those subsequently taken up remain strongly bound on the acid, up to three NO2 per heteropoly anion. The sorption of NO2 is shown to be dependent on the elemental composition of the anions of the solid acids and hence on the acid strengths of these materials. The sorbed NO2 associates with both the surface and bulk protons to form HNO2+ thus demonstrating that NO2 is capable of penetrating into the crystallographic structure of the solid acid. Prior sorption of NO2 facilitates the takeup of NO which forms N2O3. 12-tungstophosphoric acid (HPW) supported on silica produces quantitatively different but qualitatively similar results. The microporous ammonium salt of HPW produces markedly different results when exposed to NO2 with the predominant product being N2 evidently resulting from the ammonium cation functioning as a source of the reductant ammonia.
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Comparison of the Conversion of Methane and Ethane on Metal-Oxygen Cluster Compounds
Methane and Alkane Conversion Chemistry, 1995Co-Authors: S. Hong, S. Kasztelan, E. Payen, John B. MoffatAbstract:Studies of the conversion of methane and ethane on Metal-Oxygen Cluster compounds, in particular silica-supported 12-molybdophosphoric acid (H3PMo12O40, abbreviated to HPMo), show interesting similarities. The partial oxidation products from methane and ethane, formaldehyde and acetaldehyde, respectively, are obtained only in the presence of the catalyst. With both alkanes optimum results are obtained for loadings of approximately 20 wt% of HPMo on the support, corresponding to a molecular surface occupancy of 1000 A2. The conversions of the alkanes and selectivities to the various products remain constant, for a given reaction temperature, up to a catalyst pretreatment temperature of 500–550°C, a value significantly higher than the usually accepted decomposition temperature of HPMo, thereby suggesting the enhancement of the thermal stability of the active catalyst presumably resulting from a strong interaction between the support and the supported material. With ethane selectivities to acetaldehyde and ethylene of 62 and 30% have been obtained, both of which appear to be primary products. Since the oxidants appear to be primarily functioning as regenerators of the active sites on the catalysts, a mechanism in which the anionic oxygen species act as the active sites is tentatively postulated.
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A comparative study of the adsorption and reaction of nitrogen oxides on 12-tungstophosphoric, 12-tungstosilicic, and 12-molybdophosphoric acids
Journal of Catalysis, 1995Co-Authors: R Bélanger, John B. MoffatAbstract:The sorption and conversion of NO and NO2 on the three heteropoly acids (Metal-Oxygen Cluster compounds), 12-tungstophosphoric (HPW) 12-molybdophosphoric (HPMo), and 12-tungstosilicic (HSiW) acids are investigated and compared. Substantial quantities of NO2 are taken up by the tungsten-containing acids. In contrast, relatively small amounts of NO2 are sorbed by HPMo. In the absence of presorbed NO2 comparatively small quantities of NO are sorbed by any of the three solids. However, HPW and HSiW with presorbed NO2 sorb substantial quantities of NO. No evidence for reduction of either NO or NO2 is found. Temperature-programmed desorption, thermal gravimetry, infrared spectroscopy, and X-ray diffraction are employed to provide interpretive data. The results are interpreted as indicative of the formation of HNO3 from the reaction of NO2 and water as well as the substitution of the protons by NO+2 in establishing a charge balance mechanism.
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The oxidative dehydrogenation of ethane on silica-supported Metal-Oxygen Cluster compounds
Applied Catalysis A: General, 1994Co-Authors: S.s. Hong, John B. MoffatAbstract:Abstract The oxidative dehydrogenation of ethane with nitrous oxide and oxygen on silica-supported metaloxygen Cluster compounds (MOCC) has been investigated. The effects of several variables such as reaction temperature, partial pressure of reactants, nature of the oxidants (N2O and O2), residence time, loading of the catalysts, and pretreatment environment, on the conversion, product distribution and the kinetics have been studied. With nitrous oxide, on unsupported H3PMo12O40 and on the silica support no acetaldehyde was observed in the product stream while significant amounts of acetaldehyde are found with the supported MOCC. With nitrous oxide as an oxidant, acetaldehyde and ethylene were the principal products, while carbon monoxide and ethylene were the predominant products with oxygen. On H3PMo12O40the conversion of ethane and the yield of acetaldehyde have maximum values at a loading of 20 wt.-%. The results from studies of the effect of contact time suggest that acetaldehyde and ethylene are primary products. Increases in the relative amounts of the oxidants produce changes in the selectivities which are strongly dependent on the nature of the oxidant. For catalyst pretreatment temperatures greater than 500°C, the conversion of ethane and selectivity to acetaldehyde decrease. At partial pressures of ethane between 0.1 and 0.8 atm the rate of ethane conversion is of approximate order 0.8 and 0.6 in ethane and nitrous oxide, respectively and 0.7 and 0.4 in ethane and oxygen, respectively. The results show striking correspondences with those reported earlier for methane with MOCC and thus suggest that the mechanisms for the two processes may depend on the lability of the terminal oxygen atoms of the MOCC anion, the production of oxygen vacancies and the ability of the oxidant to regenerate the active oxygen sites in the anion.
Xiaoyu Ren - One of the best experts on this subject based on the ideXlab platform.
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Organic–Inorganic Hybrids Composed of Keggin-Type [PMo₁₀V₂O₄₀]⁵– Anions and Porphyrins: The Synthesis, Characterization, and Influence of Porphyrin Substituents on Optical Nonlinearities
The Journal of Physical Chemistry, 2020Co-Authors: Farooq Khurum Shehzad, Arshad Iqbal, Yunshan Zhou, Lijuan Zhang, Ting Wang, Xiaoyu RenAbstract:In order to understand the influence of porphyrin substituents on the nonlinear optical properties of organic–inorganic hybrids composed of an anionic metal–oxygen Cluster and a porphyrin cation, porphyrins bearing different functional groups (4-pyridyl, 4-hydroxyphenyl, and 3,4-dimethoxyphenyl) were chosen as prototypes to react with the well-known Keggin-type polyanion α-[PMo₁₀V₂O₄₀]⁵–, which acted as an electron acceptor; this led to formation of three electrostatically bonded disalts with formal formulas of [C₄₀H₂₈N₈][H₄PMo₁₀V₂O₄₀]₂ (1), [C₄₄H₃₂N₄O₄][H₄PMo₁₀V₂O₄₀]₂ (2), and [C₅₂H₄₈N₄O₈][H₄PMo₁₀V₂O₄₀]₂ (3), respectively. These hybrids were systematically characterized by a variety of means. The nonlinear optical properties of these compounds were studied using the Z-scan technique, conducted with irradiation at λ = 532 nm with a 6 ns duration and a repetition rate of 10 Hz at focus E₀ = 4.2 μJ. While all the hybrids showed an enhanced NLO response compared to their corresponding mother porphyrins, they also exhibited reverse saturation absorption, self-defocusing performance, and an enhancement of the second hyperpolarizability value γ in the order of γ(1) < γ(2) < γ(3), which is parallel to the electron- or charge-donor ability of the functional groups on the porphyrin. Namely, the greater the electron-donor ability of functional groups on the porphyrin, the greater the NLO response.
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Organic–Inorganic Hybrids Composed of Keggin-Type [PMo10V2O40]5– Anions and Porphyrins: The Synthesis, Characterization, and Influence of Porphyrin Substituents on Optical Nonlinearities
The Journal of Physical Chemistry C, 2020Co-Authors: Farooq Khurum Shehzad, Arshad Iqbal, Yunshan Zhou, Lijuan Zhang, Ting Wang, Xiaoyu RenAbstract:In order to understand the influence of porphyrin substituents on the nonlinear optical properties of organic–inorganic hybrids composed of an anionic metal–oxygen Cluster and a porphyrin cation, p...
G.b. Mcgarvey - One of the best experts on this subject based on the ideXlab platform.
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Microporous Metal—Oxygen Cluster Compounds (Heteropoly Oxometalates): Synthetic Variables, Nature and Source of the Porosity, Catalytic Applications, and Shape Selectivity
Advanced Catalysts and Nanostructured Materials, 1996Co-Authors: J.l. Bonardet, G.b. Mcgarvey, K. Carr, J. Fraissard, J. B. Mcmonagle, M. Seay, J.b. MoffatAbstract:Publisher Summary Heteropoly oxometalates (also known as Metal-Oxygen Cluster compounds, MOCC) have been known for more than 150 years. Although another form of oxygen polyanion exists, namely the isopolyanions the heteropoly ions are those that contain two different elements in addition to oxygen. While many possible structures are known for the heteropoly anions, that elucidated by Keggin has been more commonly studied for its catalytic and surface properties. A number of isomers of the Keggin structure are known; of these the α form appears to be the most stable and as a consequence catalytic investigations have generally focused on this isomer. The Keggin structure has a central atom (X) bonded to four oxygen atoms arranged tetrahedrally. Most of the surface and catalytic studies have employed P or Si as the central atom although, as noted earlier, many possibilities exist. The selection of P or Si as the central atom undoubtedly relates to factors of thermal stability, ease of preparation, and cost. The central XO4 tetrahedron is surrounded by 12 octahedra with a peripheral metal atom (M) at each of their approximate centers and oxygen atoms at their vertices. For catalytic purposes the more common peripheral metal atoms are W, Mo, and V. The octahedra share oxygen atoms with each other and with the central atom. The 12 octahedra are arranged in four groups of three edge-shared octahedra, M 3 0 13 , which are linked by shared corners to each other and to the central XO 4 tetrahedron. There are two types of bridging oxygen atoms, those connecting the central atom to the peripheral metal atoms and those joining each of the peripheral metal atoms.
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Microporous Metal-Oxygen Cluster compounds (heteropoly oxometalates) : synthetic variables, nature and the source of the porosity and catalytic applications
Preprints-American Chemical Society Division of Petroleum Chemistry, 1995Co-Authors: J.b. Moffat, G.b. Mcgarvey, J.l. Bonardet, K. Carr, J. Fraissard, J. B. Mcmonagle, M. SeayAbstract:During the last two decades interest in solids containing pore structures has risen markedly. In particular catalysts containing micropores have been shown to posses both interesting and avantageous properties. The solids under discussion in the present report have both similarities and dissimilarities to porous zeolites.
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MICROPOROUS-MESOPOROUS Metal-Oxygen Cluster COMPOUNDS: ION EXCHANGE, STRUCTURE RETENTION AND THE OXIDATIVE DEHYDROGENATION OF ISOBUTYRIC ACID
Multifunctional Mesoporous Inorganic Solids, 1993Co-Authors: G.b. Mcgarvey, J.b. MoffatAbstract:Metal-Oxygen Cluster compounds can be prepared with microporous-mesoporous structures by precipitation of certain of their monovalent cation salts from aqueous solution. Exchange of the cations of these salts can be achieved, although the exchange is not complete and is dependent upon the relative sizes of the entering and leaving cations. Measurements of surface areas, pore size distributions and lattice parameters, before and after cation exchange, show that the microporous-mesoporous structures are semiquantitatively retained, although not surprisingly shifted as a result of the change in size of the cation. The catalytic properties of the exchanged microporous-mesoporous Metal-Oxygen Cluster compounds, as reflected in the conversion of isobutyric acid and selectivity to the various products, show a dependence on the nature and concentration of the cations as well as the expected relationship to the elemental composition of the anions.
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The Role of the Proton in Oxidation Processes on Metal-Oxygen Cluster Compounds
Studies in Surface Science and Catalysis, 1993Co-Authors: Slavik Kasztelan, G.b. Mcgarvey, John B. MoffatAbstract:Abstract Studies of the partial oxidation of methane and the oxidative dehydrogenation of isobutyric acid on Metal-Oxygen Cluster compounds (MOCC) show that the anion of the MOCC is a prerequisite for the catalysis of these oxidation processes. However the results also clearly show the importance of the proton in both processes. The observations may be interpreted in terms of oxygen vacancies which may serve as sites for the dissociation of the gas phase oxidant, as adsorption sites for reactant molecules or as sites for the production of oxidizing species.
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Characterization of the compounds formed from the interaction of divalent cations with inorganic molecular metal—oxygen Cluster compounds
Journal of Molecular Catalysis, 1993Co-Authors: G.b. Mcgarvey, N.j Taylor, J.b. MoffatAbstract:Abstract Infrared spectroscopy, powder X-ray diffraction, differential thermal analysis and nitrogen adsorption—desorption measurements were carried out on a series of solids prepared from 12-molybdophosphoric and 12-tungstophosphoric acids and the alkaline earth hydroxides. A single crystal investigation and data analysis were done for the Ba2+ /PMo12O403− system. It is concluded that the reaction of simple divalent salts with 12-molybdophosphoric acid produces a mixture of the parent acid and a divalent compound rather than a divalent heteropoly salt.
Farooq Khurum Shehzad - One of the best experts on this subject based on the ideXlab platform.
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Organic–Inorganic Hybrids Composed of Keggin-Type [PMo₁₀V₂O₄₀]⁵– Anions and Porphyrins: The Synthesis, Characterization, and Influence of Porphyrin Substituents on Optical Nonlinearities
The Journal of Physical Chemistry, 2020Co-Authors: Farooq Khurum Shehzad, Arshad Iqbal, Yunshan Zhou, Lijuan Zhang, Ting Wang, Xiaoyu RenAbstract:In order to understand the influence of porphyrin substituents on the nonlinear optical properties of organic–inorganic hybrids composed of an anionic metal–oxygen Cluster and a porphyrin cation, porphyrins bearing different functional groups (4-pyridyl, 4-hydroxyphenyl, and 3,4-dimethoxyphenyl) were chosen as prototypes to react with the well-known Keggin-type polyanion α-[PMo₁₀V₂O₄₀]⁵–, which acted as an electron acceptor; this led to formation of three electrostatically bonded disalts with formal formulas of [C₄₀H₂₈N₈][H₄PMo₁₀V₂O₄₀]₂ (1), [C₄₄H₃₂N₄O₄][H₄PMo₁₀V₂O₄₀]₂ (2), and [C₅₂H₄₈N₄O₈][H₄PMo₁₀V₂O₄₀]₂ (3), respectively. These hybrids were systematically characterized by a variety of means. The nonlinear optical properties of these compounds were studied using the Z-scan technique, conducted with irradiation at λ = 532 nm with a 6 ns duration and a repetition rate of 10 Hz at focus E₀ = 4.2 μJ. While all the hybrids showed an enhanced NLO response compared to their corresponding mother porphyrins, they also exhibited reverse saturation absorption, self-defocusing performance, and an enhancement of the second hyperpolarizability value γ in the order of γ(1) < γ(2) < γ(3), which is parallel to the electron- or charge-donor ability of the functional groups on the porphyrin. Namely, the greater the electron-donor ability of functional groups on the porphyrin, the greater the NLO response.
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Organic–Inorganic Hybrids Composed of Keggin-Type [PMo10V2O40]5– Anions and Porphyrins: The Synthesis, Characterization, and Influence of Porphyrin Substituents on Optical Nonlinearities
The Journal of Physical Chemistry C, 2020Co-Authors: Farooq Khurum Shehzad, Arshad Iqbal, Yunshan Zhou, Lijuan Zhang, Ting Wang, Xiaoyu RenAbstract:In order to understand the influence of porphyrin substituents on the nonlinear optical properties of organic–inorganic hybrids composed of an anionic metal–oxygen Cluster and a porphyrin cation, p...