Optical Spin Polarization of a Narrow-Linewidth Electron-Spin Qubit in a Chromophore/Stable-Radical System

Photoexcited organic chromophores appended to stable radicals can serve as qubit and/or qudit candidates for quantum information applications. 1,6,7,12-Tetra-(4-tert-butylphenoxy)-perylene-3,4 : 9,10-bis(dicarboximide) (tpPDI) linked to a partially deuterated α,γ-bisdiphenylene-β-phenylallyl radical (BDPA-d₁₆) was synthesized and characterized by time-resolved optical and electron paramagnetic resonance (EPR) spectroscopies. Photoexcitation of tpPDI-BDPA-d₁₆ results in ultrafast radical-enhanced intersystem crossing to produce a quartet state ( Q ) followed by formation of a spin-polarized doublet ground state ( D ₀). Pulse-EPR experiments confirmed the spin multiplicity of Q and yielded coherence times of T_m=2.1±0.1 μs and 2.8±0.2 μs for Q and D ₀, respectively. BDPA-d₁₆ eliminates the dominant ¹H hyperfine couplings, resulting in a single narrow line for both the Q and D ₀ states, which enhances the spectral resolution needed for good qubit addressability.     

Injectivity and Graded Injectivity

In this paper, we study the injectivity and graded injectivity of modules. Injective testing sets of semiprime Noetherian rings and FBN rings are Particularly investigated. For commutative Artinian Z-graded rings, we prove that gr-injectivity implies injectivity and hence show that the gr-global dimesion and global dimesion are the same.AMS Subject Classification (1991): Primary 18G05, Secondary 18G20, 16P40.     

电极过程自由基中间体的ESR研究(Ⅳ)——脂肪胺的电解氧化

本文用自旋捕捉技术与ESR相结合的方法研究了6种脂肪胺电解氧化过程中产生的瞬态自由基。结果表明,阳极上脂肪胺氧化产生相应的正离子自由基,而后脱去α-C上的质子得到一碳中心自由基,此自由基能被捕捉剂PBN所捕获;阴极上发生H~+还原反应,所得的氢原子也可被PBN捕获。     

Intramolecular reactions of 2-indolylacyl radicals: cyclisation upon aromatic rings

The generation of 2-indolylacyl radicals from the corresponding selenoesters under reductive (tributyltin hydride-AIBN) and nonreductive (hexabutylditin, 300 W) conditions and their behaviour in cyclisation reactions upon benzene rings attached either to the indole nitrogen or the C-3 ring position have been studied.     

Vicinal alkylation-carboxymethylation of electron-poor alkenes by radical-chain reactions with O-alkyl O-silyl ketene acetals and their [3+2] annulation by reaction with O-cyclopropylcarbinyl O-silyl ketene acetals

O-Silyl ketene acetals of the type H₂CC(OR)OSiMe₂Bu^t, in which R is a tertiary or secondary alkyl group, react with electron-poor alkenes to bring about vicinal alkylation-carboxymethylation of the latter. When R is a cyclopropyldimethylcarbinyl group such reactions take a more complex course involving ring opening of the cyclopropylcarbinyl radical and lead ultimately to [3+2] annulation of the alkene.     

Xanthates derived from 1,3-dithiane and its monosulfoxide; one-carbon radical equivalents

The behaviour and synthetic scope of the C-2 centred radicals derived from 1,3-dithiane and 1,3-dithiane 1-oxide have been studied. Both radicals are available from the corresponding xanthates and have proved suitable substrates for the xanthate transfer reaction. However, the synthetic scope of the former is severely limited by the fact that it does not add to unactivated olefins. The latter on the other hand is a more promising radical precursor and undergoes smooth radical addition to a wide range of alkenes. Furthermore, subsequent transformations of some of the radical adducts confirm its utility as a synthetic equivalent of both the methyl and the formyl radical.     

The effect of dose on light-sensitivity of radicals in alanine EPR dosimeters

In this work we present a study of light-induced effects on free radicals and their transformations in gamma-irradiated pure L-alanine and in commercially available alanine detectors: rods, pellets and films. Samples irradiated to doses from 2 Gy to 4000 kGy were exposed to light from a fluorescent lamp and to ordinary daylight. The observed changes in EPR spectra of the samples were analyzed with regard to their intensity and shape. The shape analysis was based on numerical decomposition of the measured spectra into model spectra reflecting contributions of R1, R2 and R3 radical populations in the samples. The illumination of alanine dosimeters resulted in significant decrease of the central EPR line and was accompanied by distinct variations in the shape of EPR spectra. The rate of light-induced decay in spectra amplitude was found to be dependent on dose of ionizing radiation--the sensitivity to light was decreasing with increase in dose in all detectors in the 2-5x10(5) Gy dose range. The exposure of gamma-irradiated (to 300 Gy) alanine to normal, diffused daylight resulted in decay of the signal amplitude at rate about 0.5% per week. It was shown that decay in the R1 component was responsible for the observed reduction of the spectra amplitude. The observed increase in R2 contributions in samples exposed to light confirmed a hypothesis of R-->R2 radical transformations promoted by visible light. The reported effects indicate a necessity of protection of irradiated dosimeters from their prolonged exposure to light.     

Interaction of polypyromellitimide with nitrogen dioxide

The mechanism of interaction of nitrogen dioxide with aromatic polyimides is considered by the example of polypyromellitimide. The formation of stable radicals of acylarylaminoxyl, iminoxyl and phenoxyl types has been detected by electron paramagnetic resonance spectroscopy. Acylarylaminoxyl radicals were detected in polypyromellitimide after its exposure to nitrogen dioxide at room temperature followed by pumping nitrogen dioxide from the samples. Iminoxyl and phenoxyl radicals were formed during thermolysis of the nitration products of the polymer at 373 K. The proposed mechanism is based on the reaction of dimers of nitrogen dioxide in the form of nitrosyl nitrate. It was observed that intermediate radical cations and nitric oxide were formed in the primary reaction of electron transfer from the polyimide to nitrosyl nitrate. The subsequent cage reactions with participation of radical cations and nitric oxide give nitroso compounds and nitrates which are precursors of stable nitrogen-containing and phenoxyl radicals.     

Evidence of AlII Radical Addition to Benzene

Electrophilic Al^III species have long dominated the aluminum reactivity towards arenes. Recently, nucleophilic low-valent Al^I aluminyl anions have showcased oxidative additions towards arenes C−C and/or C−H bonds. Herein, we communicate compelling evidence of an Al^II radical addition reaction to the benzene ring. The electron reduction of a ligand stabilized precursor with KC₈ in benzene furnishes a double addition to the benzene ring instead of a C−H bond activation, producing the corresponding cyclohexa-1,3(orl,4)-dienes as Birch-type reduction product. X-ray crystallographic analysis, EPR spectroscopy, and DFT results suggest this reactivity proceeds through a stable Al^II radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong steric protection.     

Bis-Olefin Based Crystalline Schlenk Hydrocarbon Diradicals with a Triplet Ground State

A modular approach for the synthesis of isolable crystalline Schlenk hydrocarbon diradicals from m-phenylene bridged electron-rich bis-triazaalkenes as synthons is reported. EPR spectroscopy confirms their diradical nature and triplet electronic structure by revealing a half-field signal. A computational analysis confirms the triplet state to be the ground state. As a proof-of-principle for the modular methodology, the 4,6-dimethyl-m-phenylene was further utilized as a coupling unit between two alkene motifs. The steric conjunction of the 4,6-dimethyl groups substantially twists the substituents at the nonbonding electron bearing centers relative to the central coupling m-phenylene motif. As a result, the spin delocalization is decreased and the exchange coupling between the two unpaired spins, hence, significantly reduced. Notably, 108 years after Schlenk's m-phenylene-bis(diphenylmethyl) synthesis as a diradical, for the first time we were able to isolate its derivative with the same spacer, i.e. m-phenylene, between two radical centers in a crystalline form.