Generation and conversions of aromatic amine radical cations in acid zeolites

Garcı́a, Hermenegildo; Martí, Vicenç; Casades, Isabel; Fornés, Vicente; Roth, Heinz D.

doi:10.1039/b101383l

Cited by 26 publications

(25 citation statements)

References 28 publications

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“…It has been reported that the protonated aromatic amines can be easily oxidized to form radical cations. In our case, ii‐b was oxidized to form iii. The substituted phosphate (ii‐a) then deprotonated the radical cation (iii) by the abstraction of one proton from the methyl group on iii to form the 4E free radical (iv).…”

Section: Resultsmentioning

confidence: 64%

Ethyl‐4‐(Dimethylamino) benzoate initiation of the spontaneous polymerization of aqueous acidic adhesive formulations in the presence of a base

Bai

Liu

et al. 2013

J of Applied Polymer Sci

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This study indicated that the spontaneous polymerization of an aqueous acidic dental adhesive system containing ethyl-4-(dimethylamino) benzoate (4E) could be activated by various bases. The adhesive was prepared with a monomer mixture of bis[2-(methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA). Various amounts of base [hydroxyapatite (HAP) and its analogues, e.g., Ca(OH) 2 , NaOH, and calcium carbonate] were added. Real-time Fourier transform infrared-attenuated total reflectance spectroscopy was used to monitor the polymerization process. The pH and buffer capacity affected the degree of conversion, and the polymerization rate and induction period were evaluated. The optimal conditions for the pH of this system was between 1.0 and 1.8, and HAP had the best performance on polymerization because of its excellent buffer capacity. The mechanism for the spontaneous polymerization of the 2MP/HEMA adhesive system was proposed with 4E as an initiator.

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Section: Resultsmentioning

confidence: 64%

Ethyl‐4‐(Dimethylamino) benzoate initiation of the spontaneous polymerization of aqueous acidic adhesive formulations in the presence of a base

Bai

Liu

et al. 2013

J of Applied Polymer Sci

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“…1,2 One of the most interesting properties of acid zeolites is their ability to spontaneously generate organic radical cations upon adsorption of electron donor molecules. [3][4][5] These species can also be generated by ␥ radiation of zeolites containing organic molecules. 3,6,7 The ␥ radiation generates a free electron and a hole in the zeolite in such a way that an electron transfer from the guest to the zeolite can occur leading to the desired radical cation.…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5] These species can also be generated by ␥ radiation of zeolites containing organic molecules. 3,6,7 The ␥ radiation generates a free electron and a hole in the zeolite in such a way that an electron transfer from the guest to the zeolite can occur leading to the desired radical cation. This process is suggested to occur when the ionization energy of the guest molecule is lower than 10.0-10.5 eV.…”

Section: Introductionmentioning

confidence: 99%

Electron hole formation in acidic zeolite catalysts

Solans‐Monfort

Branchadell

Sodupe

et al. 2004

The Journal of Chemical Physics

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The formation of an electron hole on an AlO 4 H center of the H-ZSM-5 zeolite has been studied by a hybrid quantum mechanics/shell-model ion-pair potential approach. The Becke-3-Lee-Yang-Parr ͑B3LYP͒ and Becke-Half&Half-Lee-Yang-Parr ͑BHLYP͒ hybrid density functionals yield electron holes of different nature, a delocalized hole for B3LYP and a hole localized on one oxygen atom for BHLYP. Comparison with coupled cluster calculations including single and double substitutions and with perturbative treatment of triple substitutions CCSD͑T͒ and with experimental data for similar systems indicate that the localized description obtained with BHLYP is more accurate. Generation of the electron hole produces a substantial geometry relaxation, in particular an elongation of the Al-O distance to the oxygen atom with the unpaired electron. The zeolite framework stabilizes the positive charge by long-range effects. Our best estimates for the vertical and adiabatic ionization energies are 9.6 -10.1 and 8.4 -8.9 eV, respectively. Calculations for silicalite, the all-silica form of ZSM-5, also yield a localized electron hole, but the energy cost of the process is larger by 0.6 -0.7 eV. The deprotonation energy of H-ZSM-5 is found to decrease from 12.86 to 11.40 eV upon electron hole formation.

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“…Stabilized radical cations CBZ •+ were also detected in low temperature polymer matrices 31 and in zeolites. 32 The position of the maximum and the widths of spectral bands are strongly dependent on the environment. Localization of the excess electron in acetonitrile has been an intensively debatable issue (see Ref.…”

Section: Resultsmentioning

confidence: 99%

Intra- and intermolecular quenching of carbazole photoluminescence by imidazolidine radicals

et al. 2010

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Mechanisms of carbazole photoluminescence quenching by the free and chemically bound nitroxyl radicals in the model bound system "carbazole (CBZ)-imidazolidine nitroxyl radical R • " were investigated and the photophysical properties of the system were studied and com pared with those of free CBZ and R • in solution. The quantum yield and lifetime of fluores cence from the local singlet excited state of the carbazole moiety in the bound CBZ-R • system is three orders of magnitude lower than in free CBZ. The lifetime of the local triplet excited state of the carbazole moiety in the bound system is shorter than 50 ns. The rate constants for intermolecular quenching of the singlet and triplet excited states of free CBZ by R • in acetoni trile were found to be (1.4±0.1)•10 10 and (1.5±0.2)•10 9 L mol -1 s -1 , respectively. The most plausible mechanisms of both free and covalently bound carbazole luminescence quenching by nitroxyl radicals are exchange energy transfer and acceleration of internal conversion due to electron exchange.Keywords: spin labeled luminophores, laser flash photolysis, fluorescence quenching.Spin catalysis of chemical reactions by paramagnetic species occurs in triads of paramagnetic species where spin conversion in a pair of species is initiated by the third electron spin. 1,2 This phenomenon was experimentally confirmed for a number of photochemical, biochemical, and radiation chemical systems. 3-5 The third spin plays the role of the source of external magnetic field in which a spin correlated radical pair created in some (e.g., radia tion chemical) way is placed. Systematic research on spin catalysis requires some model compounds comprising a paramagnetic fragment bound to a partner from the rad ical pair.In this connection, spin labeled luminophores are of particular interest. Theoretical calculations predict a num ber of interesting effects in radiation processes involving them. 6 However, in most cases the paramagnetic center acts as an efficient quencher of the luminescence of such compounds. 4,7-9 It should be noted that it was proposed to use the reverse effect, viz., the rise of the luminescence of fluorophore-nitroxide radical dyads due to reduction of the nitroxide group, for the design of sensors for the superoxide radical, antioxidants, hydrogen peroxide in bi ological systems, 10 and for alkyl radicals in polymers. 11The accelerated internal conversion proceeding by the electron exchange mechanism is the main quenching mechanism of the fluorescence of chemically bound sys tems "luminophore-nitroxide radical". 7,8 However, some other mechanisms of quenching in these systems were pro posed, e.g., acceleration of intersystem crossing (ISC) from the excited singlet to triplet state. 7 These assumptions are based on the fact that quenching of singlet states of lumi nophores by free (chemically unbound) nitroxide radicals (this process has been studied in more details) can follow all known channels including energy transfer, 12,13 elec tron transfer, 14 ISC, 15,16 and internal convers...

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Generation and conversions of aromatic amine radical cations in acid zeolites

Cited by 26 publications

References 28 publications

Ethyl‐4‐(Dimethylamino) benzoate initiation of the spontaneous polymerization of aqueous acidic adhesive formulations in the presence of a base

Ethyl‐4‐(Dimethylamino) benzoate initiation of the spontaneous polymerization of aqueous acidic adhesive formulations in the presence of a base

Electron hole formation in acidic zeolite catalysts

Intra- and intermolecular quenching of carbazole photoluminescence by imidazolidine radicals

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