Synthesis, Characterization and Photoluminescence of Dimeric and Polymeric Metallaynes of Group 10–12 Metals Containing Conjugation-breaking Diphenylmethane Unit

A novel approach based on conjugation interruption was developed for a luminescent and thermally stable platinum(II) polyyne polymer trans-[–Pt(PBu₃)₂C≡C(C₆H₄)CH₂(C₆H₄)C≡C–] _n (1) containing the diphenylmethane chromophoric spacer. Particular attention was focused on the photophysical properties of this group 10 polymetallayne and comparison was made to its binuclear model complex trans-[Pt(Ph)(PEt₃)₂C≡C(C₆H₄)CH₂(C₆H₄)C≡CPt(Ph)(PEt₃)₂] (2) and their closest group 11 gold(I) and group 12 mercury(II) neighbors, [MC≡C(C₆H₄)CH₂(C₆H₄)C≡CM] (M = Au(PPh₃) (3), HgMe (4)). The regiochemical structures of these angular-shaped compounds were studied by various spectroscopic analyses. Upon photoexcitation, each of them emits an intense purple-blue fluorescence emission in the near UV region in dilute fluid solutions at room temperature. Harvesting of organic triplet emissions harnessed through the strong heavy-atom effects of group 10–12 transition metals was examined. These metal-containing phenyleneethynylenes spaced by the conjugation-breaking CH₂ unit were found to have high optical gaps and high-energy triplet states. The influence of metal and sp³-hybridized methylene conjugation-interrupters on the intersystem crossing rate and the spatial extent of the lowest singlet and triplet excitons was fully elucidated. Our investigations indicate that high-energy triplet states in these materials intrinsically give rise to very efficient phosphorescence with fast radiative decays. Dedicated to Professor Didier Astruc in recognition of his outstanding contribution to metallodendrimers and polymers.     

Synthesis,Characterization and Optoelectronic Properties of Dimeric and Polymeric Metallaynes Derived from 3,6-Bis(buta-1,3-diynyl)-9-butylcarbazole

A thermally stable platinum(II) polyyne polymer incorporating carbazole-based linking units, trans-[–Pt(PBu₃)₂C≡CC≡CRC≡CC≡C–] _n (R = 9-butylcarbazole-3,6-diyl), was prepared by polycondensation polymerization of trans-[PtCl₂(PBu₃)₂] with H–C≡CC≡CRC≡CC≡C–H. We report the optical absorption and photoluminescence spectra of this carbon-rich metallopolymer and compare its photophysics with its molecular dinuclear model complex trans-[Pt(Ph)(PEt₃)₂C≡CC≡CRC≡CC≡CPt(Ph)(PEt₃)₂] as well as the group 11 gold(I) congener, [(PPh₃)AuC≡CC≡CRC≡CC≡CAu(PPh₃)]. Characterization of the polymer and metal complexes was accomplished by FT-IR and NMR spectroscopies and FAB mass spectrometry. Our investigations showed that harvesting of the organic triplet emissions can be achieved by the heavy-atom effect of Pt and Au centers, which enables a very high efficiency of intersystem crossing from the S₁ singlet excited state to the T₁ triplet excited state. The influence of the metal and the C≡C chain length on the intersystem crossing rate and the spatial extent of singlet and triplet excitons is characterized. The present work indicates that high-energy triplet states intrinsically give more efficient phosphorescence in metal-containing diethynylcarbazole systems than in the corresponding bis(butadiynyl) congeners and can thus enhance the radiative decay pathway.Dedicated to Professor Richard J. Puddephatt in recognition of his outstanding contribution to inorganic and organometallic chemistry.     

Synthesis, Characterization and Photophysical Properties of Metallopolyynes and Metallodiynes of Platinum(II) with Dibenzothiophene Derivatives

Soluble, thermally stable, and easily processable platinum(II) polyyne polymers of the form trans-[–Pt(PBu₃)₂C≡CRC≡C–]_n (R = 2,8-disubstituted dibenzothiophene, 2,8-disubstituted and 3,7-disubstituted dibenzothiophene-S,S-dioxide units) have been prepared in good yields by CuI-catalyzed polymerization involving the dehydrohalogenating coupling of trans-[PtCl₂(PBu₃)₂] and HC≡CRC≡CH. We report their optical absorption and photoluminescence spectra and compare the results with the monomeric model complexes trans-[Pt(Ph)(PEt₃)₂C≡CRC≡CPt(Ph)(PEt₃)₂]. The different electronic properties and linkage geometry of the central R group lead to new organometallic materials with distinct photophysical traits. The polymer with more conjugated 3,7-disubstituted dibenzothiophene-S,S-dioxide mainly displays fluorescence band, while its isomer with less conjugated 2,8-disubstituted spacer effectively enhances the intersystem crossing rate and strong phosphorescence emission can be detected even at room temperature.     

Ring-opening polymerization of (CH3)2Si[CpMo(CO)3]2, a molecule with an –Si(CH3)2– bridge between two cyclopentadienyl ligands

The (CH₃)₂Si[CpMo(CO)₃]₂ complex (1) was synthesized and used to explore ring-opening polymerization (ROP) as a method to prepare high molecular weight polymers containing Mo–Mo bonds along their backbones. Attempts to initiate ROP of 1 using n-BuLi or PtCl₂ did not yield any polymers. The X-ray crystal structure of 1 shows that the Si center is not strained, and it is suggested that no ROP occurred because 1 is less strained than other organometallic ROP monomers, such as the silicon-bridged ferrocenophanes. Thermal ROP (TROP) of 1 was successful and yielded a polymer (M _w = 210,000 g mol⁻¹) containing both Mo–Mo single bonds and Mo≡Mo triple bonds. When CO_(g) is passed over the polymer in the solid state, the Mo≡Mo triple bonds are converted to Mo–Mo single bonds. Attempts to increase the yield of the TROP polymer by increasing the reaction times led to polymer decomposition. The decomposition is likely caused by the weakness of the Mo–Mo bond, cleavage of which causes the polymer to degrade.     

Cyano-Bridged Heteropolynuclear Ni(II), Cu(II) and Cd(II) Complexes, [M(deten)2Ni(μ-CN)2(CN)2] n

Three new complexes [M(deten)₂Ni(μ-CN)₂(CN)₂] _n (M = Ni, Cu and Cd, deten = N,N-diethylethylenediamine) have been synthesized and characterized by chemical, thermal analysis, FT-IR and Raman spectroscopies. The crystal structure of the Cd complex has been determined by X-ray single crystal diffraction. Structural study reveals that the Ni²⁺ and Cd²⁺ ions are located on inversion centers, and adopt slightly distorted square-planar and octahedral geometries, respectively. In the crystal structure, the intermolecular N–H⋯N hydrogen bonds link the polymeric chains into a two dimensional network. Vibrational spectral data indicate the presence of two ν(C≡N) for complexes can be assigned to the terminal and bridging cyanides. The decomposition reaction take places in the temperature range 30–1000 °C in the static air atmosphere.     

Novel carbonaceous coupling products containing sulphur

Summary The coupling of alkali ethynides with CSCl₂, SOCl₂, or SO₂Cl₂ results in new carbonaceous polymeric products; their structures were studied by FTIR and XPS spectra, and the assumptions on reaction mechanism were made with respect to the found elemental composition and model calculations. These macromolecular products, obtained in the yields of 80–92%, contain chlorine in the chain terminals, and alkyne sequences along with inserted C=S, S=O or SO₂ groups. These inserted sulphur groups contribute to the stability of alkyne sequences as evidenced by FTIR spectra. Soluble thioketone iPr₃SiC≡C–CS–C≡CSiiPr₃ (2) prepared by similar coupling of iPr₃SiC≡CLi (1) with CSCl₂ in the yield of 72%, was considered as a support of the suggested coupling mechanism. Similarly monomolecular sulfoxide iPr₃SiC≡C–SO–C≡CSiiPr₃ (3) was prepared by coupling of iPr₃SiC≡CLi (1) with SOCl₂ in the yield 75%.     

Synthesis and gas permeability of poly(<Emphasis Type="Italic">p</Emphasis>-phenyleneethynylene)s having bulky alkoxy or alkyl groups

Dipropynylbenzene with branched alkoxy and alkyl groups [CH₃C≡CRC₆H₂RC≡CCH₃, R = 2-methylpropoxy (1a), 3-methylbutoxy (1b), 4-methylpentoxy (1c), cyclohexylmethoxy (1d), 2-ethylhexoxy (1e), 2-octoxy (1f), 2-ethylhexyl (1g), and 2-octyl (1h)] were polymerized with Mo(CO)₆ in the presence of 4-(trifluoromethyl)phenyl to afford poly(2,5-di(alkoxy or alkyl)-p-phenyleneethynylene)s (2a–h). Polymer 2a was insoluble in any solvents, but the other polymers (2b–h) were soluble in common organic solvents. The polymers with relatively long side chains (2e–h) had high molecular weight over 1.6 × 10⁴ and gave free-standing membranes by solution-casting method. The densities of membranes of 2e–h were 0.914–0.998, and their fractional-free volume values were relatively large (0.094–0.158). The oxygen permeability coefficients of membranes of 2e–h were 18.4, 12.7, 4.85, and 19.3 barrers, respectively. It was found that poly(p-phenyleneethynylene) with 2-octyl side groups, which have the branch at the nearest position from main chain, exhibited the highest gas permeability.     

Preparation of Polymers Containing Metal–Metal Bonds along the Backbone Using Click Chemistry

The [(η⁵-C₅H₄(CH₂)₃OC(O)(CH₂)₂C≡CH)Mo(CO)₃]₂ complex (1) was synthesized and used to explore the feasibility of using the Huisgen cycloaddition reaction (a click reaction) to incorporate molecules with metal–metal bonds into polymer backbones. In a model reaction, coupling of 1 with benzyl azide was observed in 24 h using Cp*Ru(PPh₃)₂Cl as a catalyst. In contrast, the reaction of 1 with benzyl azide using a CuBr/ligand catalyst (where the ligand is either PMDETA or bipyridine), resulted in disproportionation of the Mo–Mo unit in 1. Complex 1 was also coupled with telechelic azide-terminated polystyrene oligomers. With either the CuBr/PMDETA or CuBr/bipyridine catalyst, disproportionation of the Mo–Mo bonded unit occurred before complete coupling was observed. The reaction was also slow when the Cp*Ru(PPh₃)₂Cl catalyst was used; however, no disproportionation products were observed and a high molecular weight polymer (M _n = 120,000 g/mol) was produced. The Cp*Ru(PPh₃)₂Cl catalyst was also used to couple 1 with azide-terminated poly(ethylene glycol). After 15 h, this reaction produced a polymer with M _n = 73,000 g mol⁻¹. It is concluded that, although somewhat slow, click chemistry using the Cp*Ru(PPh₃)₂Cl catalyst is an excellent method for synthesizing high molecular weight polymers with metal–metal bonds along the backbone.     

Hydrosilylation Synthesis of New Ferrocenylene Copolymers Containing Carbosilylene,Carbosiloxy and Cyclopentadienyliron Dicarbonyl Bridges

Bifunctional organometallic silicon precursor monomers and substrates FC(SiMe₂H)₂ (1) [FC = (η⁵-C₅H₄)Fe(η⁵-C₅H₄)]; FC(SiMe₂(CH₂)_xCH=CH₂)₂ [x = 0 (2), 1 (3)], [η⁵-C₅H₄-SiMe₂(CH₂)_xCH=CH₂)]Fe(CO)₂SiMe₂(CH₂)_xCH=CH₂ x = 0 (4), 1 (5) and (η⁵-C₅H₄-SiMe₂H)Fe(CO)₂SiMe₂H (6) have been used to make a series of new iron containing polymers via hydrosilylation reactions. In addition to the vinyl- and allyl-containing substrates 2, 3, 4 and 5 the organosilicon compounds [CH₂=CHSiMe₂]₂O, 1,4-(H₂C=CH-SiMe₂)₂C₆H₄ and (HC≡CH–SiMe₂)₂O were also used as substrates for the hydrosilylation reaction. The reactions between the various SiH and CH=CH₂ and C≡C functionalities were performed in the presence of Pt(0) catalyst and resulted in regioselective (β-isomer and β-(E) isomer) products as determined by NMR spectroscopy. Molecular weights of all the polymers were determined by Gel Permeation Chromatography, which revealed oligomeric materials with narrow polydispersity. Cyclic voltammetric studies of exhibited single reversible redox processes due to the Fe(II)/Fe(III) couple when present, and irreversible oxidation for the presence of any Fp Fe atom. This article is dedicated to Professor Astruc.     

DNA binding of mixed-metal supramolecular Ru, Pt complexes

The mixed-metal supramolecular complexes [(tpy)Ru(PEt₂Ph)(dpp)PtCl₂](PF₆)₂ and [(tpy)Ru(PEt₂Ph)(bpm)PtCl₂](PF₆)₂ are of interest in that they couple light absorbing ruthenium centers to a reactive metal site through a communicative bridge (tpy=2,2^′:6^′,2^′′-terpyridine, BPM=2,2^′-bipyrimidine and DPP=2,3-bis(2-pyridyl)pyrazine). These systems have been studied and shown to avidly bind to DNA, greatly reducing its mobility through an agarose gel.     

Vapochromism and Crystallization-Enhanced Emission of 1,1-Disubstituted 2,3,4,5-Tetraphenylsiloles

Effects of solvent vapor on the photoluminescence (PL) of 2,3,4,5-tetraphenylsiloles carrying different 1,1-substituents [(PhC)₄SiRR′, R = Ph, R′ = CH₃ (2); R = Ph, R′ = C≡CH (3); R = R′ = C≡CH (4)] were investigated. The emission of the silole spots on the TLC plates can be turned “off” and “on” continuously and reversibly by wetting by, and de-wetting from, vapors of organic solvents, respectively. After fumigation by solvent vapor, the thin film of 4 coated on the quartz substrate emits stronger and bluer PL owing to the transformation of film morphology from the amorphous to the crystalline phase. Analysis by X-ray diffraction reveals that the molecular conformations of the crystals of 2–4 are locked and stabilized by multiple C–H···π hydrogen bonds. This structural rigidification has made the silole crystals stronger emitters.     

Polymerization of α-olefins and Hydrogenolysis of the Resulting Polyolefins with Hafnium Hydrides Supported on Silica

The reaction of Hf(CH₂ tBu)₄ with a silica surface treated at 800 °C affords the unique single site (≡SiO)Hf(CH₂ tBu)_3, 1, ((≡SiO) = silica surface ligand). Reaction of 1, with dihydrogen at temperatures (θ) ranging from 100 °C to 250 °C leads to different surface hydrides. At θ ≤ 100 °C, there is formation of [(≡SiO)Hf(CH₂ tBu)(H)₂], 2. For 100 ≤ θ ≤ 200 °C, 2 affords, [(≡SiO)₂Hf(H)₂], 3, and [(≡SiO)₃SiH]. For 150 ≤ θ ≤ 250 °C, 3, is totally converted into [(≡SiO)₃Hf(H)], 4, and [(≡SiO)₂Si(H)₂]. These different surface hafnium hydrides 2–4, which are obtained simultaneously but in various proportions were referred to as [Hf]_θ–H, (θ = 75, 100, 125, 150 and 250 °C). [Hf]₁₅₀–H is the most active catalyst in α olefin (ethylene, propene, isobutylene) polymerization at 25 °C and in polyolefin depolymerization at 150 °C under H₂ atmosphere. Although, there is a clear correlation between the catalytic activity both in polymerization and in depolymerization, and the amount of 3 and 4, it is not possible to establish which between the mono and the bis-hydride is the most active.     

Ru(0) complex catalyzed polyaddition New synthesis of poly(alkylenebenzoxazole) and poly(alkylenebenzimidazole)

Summary The reactions of α,ω-diyne, HC≡C(CH₂)_mC≡CH (m = 6 and 8), with 3,3'-diaminobenzidine and with 3,3'-diamino-4,4'-dihydroxybiphenyl in the presence of RU₃(CO)₁₂-PPh₃ catalyst give the corresponding poly(alkylenebenzoxazole)s and poly(alkylenebenzimidazole)s, respectively. The former polymers obtained from the equimolar reaction of the monomers are partly soluble in polar organic solvents such as DMF, DMSO, and NMP, while the poly(benzimidazole)s are soluble in these solvents. GPC measurement shows the molecular weights of the polymers, M _n of 4.8−14.1×10³ and M _w of 6.4−19.7×10³. Received: 24 November 1998/Revised version: 21 December 1998/Accepted: 24 December 1998     

H/D Exchange on Silica-Grafted Tantalum(V) Imido Amido [(≡SiO)<Subscript>2</Subscript>Ta<Superscript>(V)</Superscript>(NH)(NH<Subscript>2</Subscript>)] Synthesized from Either Ammonia or Dinitrogen: IR and DFT Evidence for Heterolytic Splitting of D<Subscript>2</Subscript>

The silica-grafted Ta^(V) imido amido complex [(≡SiO)₂Ta(NH)(NH₂)], 2, obtained from the reaction of either ammonia or dinitrogen plus hydrogen with the silica-grafted hydrides [(≡SiO)₂Ta^(III)H], 1a, and [(≡SiO)₂Ta^(V)H₃], 1b, undergoes H/D exchange with D₂. In situ IR spectroscopy shows that the fully labelled compound [(≡SiO)₂Ta(ND)(ND₂)], 2-d, can be obtained by moderate heating (60 °C, 3 h) under D₂ atmosphere (550 torr, 300 eq. with respect to Ta), and that the exchange is reversible. The observed stretching and bending frequencies of 2-d are in agreement with the expected isotopic shift upon H/D replacement with respect to literature values reported for 2 and have been corroborated by the independent synthesis of 2-d by reaction of deuterated 1a and 1b with N₂ and D₂. Density functional theory (DFT) calculations, performed using a periodic or a cluster model, explored the structures and energetics of all minima involved in the reaction with H₂ and showed that among the explored pathways the energetically preferred mechanisms for H₂ reaction with [{(μ-O)[(HO)₂SiO]₂}Ta^(V)(NH)(NH₂)], 2q, is the heterolytic cleavage of either the imido Ta=N or the amido Ta-N bonds, to yield respectively [{(μ-O)[(HO)₂SiO]₂}TaH(NH₂)₂], 3q (ΔE = −9.5 kcal mol⁻¹ and ΔG_298K = +2.6 kcal mol⁻¹ with respect to 2q) and [{(μ-O)[(HO)₂SiO]₂}Ta(NH)(NH₃)], 4q (ΔE = −6.0 kcal mol⁻¹ and ΔG_298K = +7.9 kcal mol⁻¹ with respect to 2q). All activation barriers are moderate (between 17.7 and 30.2 kcal mol⁻¹) in agreement with the observed mild heating conditions necessary for the reaction to occur.     

PdCl2(P(OPh)3)2 Catalyzed Coupling and Carbonylative Coupling of Phenylacetylenes with Aryl Iodides in Organic Solvents and in Ionic Liquids

Efficient cross-coupling and carbonylative coupling of terminal alkynes with aryl iodides catalyzed by PdCl₂(P(OPh)₃)₂ in the presence of NEt₃ in toluene and in ionic liquids is described. In imidazolium ionic liquids, [bmim]PF₆ or [mokt]PF₆ (bmim = 1-butyl-3-methyl imidazolium cation, mokt = 1-methyl-3-octyl imidazolium cation) catalyst was recycled and used in four concecutive catalytic cycles with high activity. In the absence of aryl iodide the same catalytic system catalyzed head-to-tail dimerization of phenylacetylene to the 1,3-diphenyl enyne, trans-PhC ≡ C–C(Ph)=CH₂, with a yield of 85%.     

Greenhouse gas emissions and final compost properties from co-composting bovine specified risk material and mortalities with manure

The increased disposal costs of cattle specified risk materials (SRM) have reduced the competitiveness of the Canadian beef industry. The SRM materials include the skull, brain, trigeminal ganglia, eyes, palatine tonsils, spinal cord and dorsal root ganglia. This study investigates greenhouse gas (GHG) emissions and final compost properties from open windrow co-composting of manure with bovine SRM and mortalities. There were two compost treatments with four replications: SRMC consisting of SRM, cattle manure and barley straw and COWC consisting of cattle mortalities, cattle manure and barley straw. Average windrow temperature was higher (P < 0.05) for SRMC (47.1°C) than for COWC (44.1°C) over the first 139 days. The final compost coliform count, moisture, pH and TC contents were not significantly different between treatments while TN and available N (NH₄ ⁺ + NO₃ ⁻ + NO₂ ⁻) were lower for SRMC than for COWC. The average surface GHG flux from SRMC were 24.3 g C day⁻¹ m⁻² and 0.17 g N day⁻¹ m⁻² for CO₂ and N₂O, respectively, and were not significantly different from those from COWC (31.6 g C day⁻¹ m⁻² and 0.17 g N day⁻¹ m⁻² for CO₂ and N₂O, respectively), but CH₄ emissions from SRMC (0.47 g C day⁻¹ m⁻²) were lower than from COWC (1.57 g C day⁻¹ m⁻²). While a few large bones were left in the cattle mortality treatment, composting decomposed all SRM suggesting that it may be a viable alternative to rendering for SRM disposal.     

Poly(di(ω-alkylphenyl)stannane)s

Poly(di(ω-alkylphenyl)stannane)s, [Sn(C _n H_2n Ph)₂] _m with n = 2–4, and a copolymer of di(3-propylphenyl)stannane and dibutylstannane of weight-average molar masses of 2–8 · 10⁴ g/mol were synthesized by dehydropolymerization of stannanes of the composition H₂SnR₂ using Wilkinson’s catalyst [RhCl(PPh₃)₃]. At least two methylene groups were required as spacers between the phenyl group and the tin atom for polymerization to occur. The polystannanes were characterized by, among other techniques, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, thermal analysis and X-ray diffraction. The polymers featured properties different from those of the corresponding poly(dialkylstannane)s. Specifically, the [Sn(C _n H_2n Ph)₂] _m family displayed glass transitions at remarkably low temperatures, down to ca. −50 °C, and a lower value for a copolymer (−68 °C). Polymers [Sn(C_nH_2nPh)₂]_m with n = 2 and 3 and a copolymer at room temperature were of a gel-like concistence, which enabled facile orientation with shear forces. Finally, the temperature-dependent electrical conductivity was determined for poly(di(3-propylphenyl)stannane), which followed the law of typical semiconductors, with an activation energy for conduction of 0.12 eV.     

Conformational analysis for hydrated ethylene oxide oligomer models by quantum chemical calculations

Hydrate effects on the conformations of ethylene oxide oligomers (EO-x, x = 1–8 mers) were examined using quantum chemical calculations (QCC). Conformational analyses were carried out by RHF/6-31G. The models were constructed by locating a water molecule to each ether–oxygen in the structures optimized for non-hydrate oligomers. Hydrate ratio, h (h = H₂O_mol/O_{mol in oligomer}), was set from 0 to 1.0. The six type conformations with repeated units of O–C, C–C and C–O bonds were examined. Conformational energy, E _c (HF), was calculated as difference between the energy of oligomer with water molecules and that of non-hydrogen and/or hydrogen bonding water molecules. Hydrate energies for each conformer, ∆μ _h (kcal/m.u., based on E _c in non-hydrate state), were negative and linearly decreased with the increase of h values, and such effects with the increase of h values were weaken with increasing x values. These results were consistent with our previous results calculated using the permittivity, ε (ε = 0–80.1), by QCC. In non-hydrate (h = 0), the (ttt) _x conformers were the most stable independent of x. However, in hydrate states (h = 0.44–0.67), the (tg⁺t) _x conformers were the most stable independent of x values, and in h = 1, the (tg⁺t)₈ conformer (8-mer) was most stable [∆E _c(g) = −1.3 kcal/m.u., ∆E _c(g): energy difference between a given oligomer and the (ttt) _x oligomer]. These results supported the experimental those based on NMR analyses using dimethoxyethane and triglyme solutions. Molecular lengths (l) of (tg⁺t) _x , (tg⁺g⁻) _x and (g⁺g⁺g⁺) _x conformers having higher x values significantly decreased with increasing h values. Such contraction with hydration, however, was independent of ΔE _c(g) values of each conformer.     

Kinetic Study of the Prooxidant Effect of α-Tocopherol. Hydrogen Abstraction from Lipids by α-Tocopheroxyl Radical

A kinetic study of the prooxidant effect of α-tocopherol was performed. The rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) by α-tocopheroxyl radical in toluene were determined, using a double-mixing stopped-flow spectrophotometer. The second-order rate constants (k _p) obtained are <1 × 10⁻² M⁻¹ s⁻¹ for 1, 1.90 × 10⁻² M⁻¹ s⁻¹ for 2, 8.33 × 10⁻² M⁻¹ s⁻¹ for 3, 1.92 × 10⁻¹ M⁻¹ s⁻¹ for 4, and 2.43 × 10⁻¹ M⁻¹ s⁻¹ for 5 at 25.0 °C. Fatty acid esters 3, 4, and 5 contain two, four, and six –CH₂– hydrogen atoms activated by two π-electron systems (–C=C–CH₂–C=C–). On the other hand, fatty acid ester 2 has four –CH₂– hydrogen atoms activated by a single π-electron system (–CH₂–C=C–CH₂–). Thus, the rate constants, k _abstr/H, given on an available hydrogen basis are k _p/4 = 4.75 × 10⁻³ M⁻¹ s⁻¹ for 2, k _p/2 = 4.16 × 10⁻² M⁻¹ s⁻¹ for 3, k _p/4 = 4.79 × 10⁻² M⁻¹ s⁻¹ for 4, and k _p/6 = 4.05 × 10⁻² M⁻¹ s⁻¹ for 5. The k _abstr/H values obtained for 3, 4, and 5 are similar to each other, and are by about one order of magnitude higher than that for 2. From these results, it is suggested that the prooxidant effect of α-tocopherol in edible oils, fats, and low-density lipoproteins may be induced by the above hydrogen abstraction reaction.     

Structures and pyroelectric properties for [111]-oriented Mn-doped rhombohedral 0.36PIN-0.36PMN-0.28PT crystal

The crystal structures, pyroelectric properties, and thermal stability of [111]-oriented 0.5 mol% Mn-doped 0.36Pb(In_1/2Nb_1/2)O₃-0.36Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ (Mn-0.36PIN-0.36PMN-0.28PT) ternary single crystal were investigated. The temperature dependence of the Raman spectra and dielectric properties revealed that the crystal exhibited a rhombohedral (R) structure at room temperature, and ferroelectric R → tetragonal (T) and ferroelectric T to paraelectric cubic (C) phase transitions at 130 and 175°C respectively. The single crystal had a high remnant polarization of P_r = 38 μC cm^–2 and coercive field of E_C = 12 kV cm^–1 at room temperature and a frequency of f = 100 Hz. The values of P_r and E_C decreased with increasing temperature, exhibiting anomalies near their phase-transition temperatures, which coincided with changes in the Raman spectra and dielectric properties. Furthermore, at 25°C and f = 100 Hz, the single crystal had high pyroelectric coefficients of p = 8.7 × 10⁻⁴ C m⁻² K⁻¹, figures of merit for the current responsivity of F_i = 3.5 × 10⁻¹⁰ m V⁻¹, the voltage responsivity of F_v = 0.08 m² C⁻¹, and the detectivity of F_d = 30.1 × 10⁻⁵ Pa^−1/2. These values were weakly dependent on temperature below 120°C. In addition, the room-temperature pyroelectric coefficients of the ternary single crystal maintain over 83% of the original value at thermal annealing temperatures below 120°C. These outstanding pyroelectric properties, together with high thermal stability, indicate that [111]-oriented rhombohedral Mn-0.36PIN-0.36PMN-0.28PT ternary single crystal is a new potential candidate for infrared detection applications.