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Guest Inclusion Modulates Concentration and Persistence of Photogenerated Radicals in Assembled Triphenylamine Macrocycles
摘要： Substituted triphenylamine (TPA) radical cations show great potential as oxidants and as spin containing units in polymer magnets. Their properties can be further tuned by supramolecular assembly. Here, we examine how the properties of photogenerated radical cations, intrinsic to TPA macrocycles, are altered upon their self-assembly into 1D columns. These macrocycles consist of two TPAs and two methylene ureas which drive the assembly into porous organic materials. Advantageously, upon activation the crystals can undergo guest exchange in a single-crystal-to-single-crystal transformation generating a series of isoskeletal host-guest complexes whose properties can be directly compared. Photoinduced electron transfer, initiated using 365 nm LED’s, affords radicals at room temperature as observed by EPR spectroscopy. The line shape of the EPR spectra and the quantity of radicals can be modulated by both polarity and heavy atom inclusion of the encapsulated guest. These photogenerated radicals are persistent, with half-lives between 1-7 days and display no degradation upon radical decay. Re-irradiation of the samples can restore the radical concentration back to a similar maximum concentration, a feature that is reproducible over several cycles. EPR simulations of a representative spectrum indicate two species, one containing two N hyperfine interactions and an additional broad signal with no resolvable hyperfine interaction. Intriguingly, TPA analogs without bromine substitution also exhibit similar quantities of photogenerated radicals, suggesting that supramolecular strategies can enable more flexibility in stable TPA radical structures. These studies will help guide the development of new photoactive materials.
关键词： photoinduced electron transfer,supramolecular assembly,radical cations,triphenylamine,EPR spectroscopy
更新于2025-09-12 10:27:22
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Spectroscopic studies on Cr3+ doped ZnCdO nanostructures for optoelectronic device application
摘要： Cr3+ ion doped ZnCdO nanopowder was synthesized by chemical solution method. Structural (X-ray di?raction, surface morphology and energy dispersion), di?erent spectroscopic studies like FT-IR, EPR, Optical and PL were performed on the prepared nanopowders. From the XRD pattern, it was con?rmed that the crystalline size of the nanopowder was at nanoscale range. The morphological surface of the powder was analyzed by SEM. FT-IR showed the trademark assimilation groups identi?ed with the metal oxides and additionally other natural particles. EPR spectrum exhibited characteristic Cr3+ ion resonance signal at g = 1.98. By connecting EPR and optical information, the holding parameters have been resolved. From the optical absorption studies, the assimilation groups are assessed. Photoluminescence studies showed that the out?ow groups are in UV and blue area. These parameters recommended that Cr3+ ions are in octahedral site symmetry with covalent bonding nature.
关键词： Cr3+ ion doped ZnCdO nanopowder,EPR,FTIR,XRD,Optical,PL
更新于2025-09-12 10:27:22
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Monitoring of the Mechanism of Mn Ions Incorporation into Quantum Dots by Optical and EPR Spectroscopy
摘要： Synthesis of nanoparticles doped with various ions can significantly expand their functionality. The conditions of synthesis exert significant influence on the distribution nature of doped ions and therefore the physicochemical properties of nanoparticles. In this paper, a correlation between the conditions of synthesis of manganese-containing cadmium sulfide or zinc sulfide nanoparticles and their optical and magnetic properties is analyzed. Electron paramagnetic resonance was used to study the distribution of manganese ions in nanoparticles and the intensity of interaction between them depending on the conditions of synthesis of nanoparticles, the concentration of manganese, and the type of initial semiconductor. The increase of manganese concentration is shown to result in the formation of smaller CdS-based nanoparticles. Luminescent properties of nanoparticles were studied. The 580 nm peak, which is typical for manganese ions, becomes more distinguished with the increase of their concentration and the time of synthesis.
关键词： manganese,electron paramagnetic resonance (EPR),nanoparticles,quantum dots,zinc sulfide,cadmium sulfide,luminescence
更新于2025-09-12 10:27:22
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Mesoscopic two-mode entangled and steerable states of 40?000 atoms in a Bose-Einstein-condensate interferometer
摘要： Using criteria based on superselection rules that apply to massive bosons but not to photons, we analyze the quantum correlations between the two condensate modes of a Bose-Einstein condensate interferometer [described in Egorov et al., Phys. Rev. A 84, 021605 (2011)]. We show that the observation of interference fringes can only be explained by Einstein-Podolsky-Rosen steering correlations between the two modes. Moreover, the size of the two-mode correlation linked to the fringe visibility will place a lower bound on the mean number of atoms of the (pure) two-mode steerable state. In order to determine the two-mode correlations, we develop a multimode theory describing the dynamics of the condensate atoms and the thermal fraction through the interferometer sequence, in agreement with the experimentally measured fringe visibility. We thus present experimental evidence for two-mode entangled states genuinely involving 40 000 87Rb atoms, and for two-way steerability between two groups of 20 000 indistinguishable atoms.
关键词： Bose-Einstein condensate,EPR steering,quantum correlations,superselection rules,interferometer
更新于2025-09-12 10:27:22
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Experimental test of error-tradeoff uncertainty relation using a continuous-variable entangled state
摘要： Heisenberg’s original uncertainty relation is related to measurement effect, which is different from the preparation uncertainty relation. However, it has been shown that Heisenberg’s error disturbance uncertainty relation is not valid in some cases. We experimentally test the error-tradeoff uncertainty relation by using a continuous-variable Gaussian Einstein–Podolsky–Rosen (EPR)-entangled state. Based on the quantum correlation between the two entangled optical beams, the errors on amplitude and phase quadratures of one EPR optical beam coming from joint measurement are estimated, respectively, which are used to verify the error–tradeoff relation. Especially, the error–tradeoff relation for error-free measurement of one observable is veri?ed in our experiment. We also verify the error–tradeoff relations for nonzero errors and mixed state by introducing loss on one EPR beam. Our experimental results demonstrate that Heisenberg’s error–tradeoff relation is violated in some cases for a continuous-variable system, while the Ozawa’s and Branciard’s relations are valid.
关键词： continuous-variable Gaussian Einstein–Podolsky–Rosen (EPR)-entangled state,error-tradeoff uncertainty relation,quantum correlation,Heisenberg’s uncertainty relation,joint measurement
更新于2025-09-11 14:15:04
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Similarity and Specificity of Chlorophyll <i>b</i> Triplet State in Comparison to Chlorophyll <i>a</i> , as Revealed by EPR/ENDOR and DFT Calculations.
摘要： An investigation of the photoexcited triplet state of chlorophyll (Chl) b has been carried out by means of Electron Nuclear Double Resonance (ENDOR), both in frozen organic solvent and in protein environment provided by the Water-Soluble Chlorophyll Protein of Lepidium virginicum. Density functional theory (DFT) calculations have allowed the complete assignment of the observed hyperfine couplings corresponding to the methine protons and the methyl groups, leading to a complete picture of the spin density distribution of the triplet state in the tetrapyrrole macrocycle. The triplet state properties of Chl b were found to be similar in many respects to those previously reported for Chl a, although some specificities have been highlighted. Concerning the spin density distribution, the differences are manly localized on the carbon atoms close to the formyl group which, in Chl b, replaces the methyl group of Chl a.
关键词： EPR/ENDOR,triplet state,DFT calculations,Chlorophyll b,spin density distribution
更新于2025-09-11 14:15:04
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Investigation of luminescence mechanism of Nd3+-doped calcium aluminate glasses: Effect of glass-formers
摘要： The relationship between the luminescence properties and the glass structure of Nd3+-doped CaO-Al2O3-(B2O3, SiO2, or Ga2O3) glasses are investigated. The luminescence properties of CaO-Al2O3-B2O3 system are twice as much as that of the CaO-Al2O3-(SiO2 or Ga2O3) system. The glass structure and the coordination environment of the Nd3+ ions were investigated using nuclear magnetic resonance, Raman and electron paramagnetic resonance spectroscopy. All Al, Ga, and Si atoms are four coordinated. The B atoms have three- and four-coordinated boron units, however, most of them are three coordinated. The hyper?ne sublevel correlation spectra reveal that the Al and B nuclei are in the coordination sphere of Nd3+ ions for aluminoborate glasses; however, only 27Al signals could be observed for aluminosilicate and aluminogallate glasses. Owing to the increased number of AlO4-BO3 connections and 11B nuclei around the Nd3+ ions, B has a signi?cant e?ect on the luminescence properties of the Nd3+ ions. The increase in GaO4 or SiO4 does not change the three dimensional-tetrahedral network, and the coordination environment of Nd3+ ions varies slightly. Thus, the e?ect of Ga2O3 and SiO2 on the luminescence properties of the Nd3+ ions is not as great as that of B2O3.
关键词： Glass structure,Local environments of rare-earth ions,EPR,Luminescence properties,NMR
更新于2025-09-10 09:29:36
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Hybrid Nanostructures for Cancer Theranostics || Nanostructures for Externally Triggered Chemo/Thermal Therapies
摘要： Cancer is the most common cause of death globally despite improvement in early detection, life-style changes, and advances in radiotherapy, immunotherapy, chemotherapy, and molecular medicine. The American Cancer Society estimated 1,688,780 cases of cancer and 600,920 deaths in the USA in 2017 alone. Problems with current therapies include: invasive procedures, systemic side effects from the nonspecific nature of chemotherapy drugs, and drug-resistant tumors. In addition to limited efficacy, the side effects of current treatments include anemia, bleeding or clotting, loss of bone density, bowel dysfunction, fatigue, hair loss, damage to the heart, immune suppression, infertility, lung dysfunction, lymphedema, mental deficits, nausea, pain, sexual dysfunction, skin changes, weight loss or gain, and urinary and bladder problems. Radiation and chemotherapies comprise the bulk of cancer treatment methods in current practice, and the off-target effects are primarily due to the nonspecific toxicity of these methods. Obviously, limiting nonspecific toxicity will improve patients’ quality of life, while not affecting tumor directed dose—this provides the motivation to pursue tumor-targeted nanomedicine. Further, many current therapy methods do not adequately address the individual patient differences resulting from inter and intra-tumor heterogeneity. Ideal disease treatment would noninvasively deliver therapy to only the target, limiting side effects due to the nonspecific drug action, and expose the tumor to a sufficient amount of drug, or other therapy such as heat or radiation. Multifunctional nanoparticles (NPs), which aid in the diagnosis (generally by acting as a contrast agent for traditional diagnostic imaging modalities), possibly targeted to the specific molecular phenotype of tumors, and which also deliver therapy (nanotheranostics) offer benefits not possible with other therapies. Only about 1% of current therapeutic agents deposit in tumors; thus, the vast majority of injected drugs are either excreted or end up in undesired tissues. In addition to not effectively treating the disease, exposing the tumors to such low concentrations of chemotherapeutic agents also artificially selects for cells that can tolerate the drug, leading to resistance. Incorporating drugs into nanoconstructs that can be noninvasively tracked for delivery to the tumor and activated at the disease site, offers a potential solution to both the drug-delivery and toxicity/efficacy problems of current chemotherapies. Besides drug delivery, NPs can also be designed and used to thermally ablate the tumor using energy from an external source, thereby avoiding invasive surgical procedures. The subcellular size (in the tens to hundreds of nanometers, similar in size to organelles) of NPs makes them exceptionally well suited for use in drug delivery and/or as absorbers for certain wavelengths of light. They can circulate for a relatively long period because they avoid rapid filtration by the spleen and can pass through Kupffer cell sieve plates. A long circulation time gives them a greater percentage of injected dose accumulating in the desired location. Tumors generally exhibit a more porous vasculature and poorer lymphatic circulation than normal tissue, allowing more and larger particles to cross over between the blood vessels and intercellular space and build up there. This is called enhanced permeability and retention (EPR), and can cause NPs to build up in the tumor, provided they can circulate long enough.
关键词： Drug delivery,Cancer,Thermal ablation,Enhanced permeability and retention (EPR),Externally triggered NPs,Nanotheranostics,Nanomedicine
更新于2025-09-10 09:29:36
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Investigations of the electron paramagnetic resonance parameters and defect structures for Cu2+ ions in BeO crystal with trigonally distorted tetrahedral symmetry
摘要： The electron paramagnetic resonance(EPR) parameters (g factors gi and hyperfine structure constants Ai, where i=x, z) for Cu2+ ions embedded in beryllium oxide (BeO) crystal at Be2+ sites with C3v local symmetry have been calculated by the complete diagonalization method (CDM) and high-order perturbation theory method (PTM). The calculated results from the two methods are in reasonable agreement with the observed data available. The defect structural data of the trigonal Cu2+ center in beryllium oxide are determined from the calculations and analyses.The calculated results show that the Be2+ ions are replaced by Cu2+ ions in BeO crystal and the ligands undergo outward movement.
关键词： Electron paramagnetic resonance (EPR),Crystal - and ligand- field theory,Defect structure,BeO:Cu2+
更新于2025-09-10 09:29:36
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EPR study of luminescence mechanism of Nd3+-doped borate aluminum glass
摘要： The luminescence mechanisms of Nd3+: B2O3-Al2O3-CaO glasses with different amounts of B2O3 were investigated based on their electron paramagnetic resonance spectra and luminescence properties. The results of the echo-detection field sweep exhibited two different maxima indicating that Nd3+ ions occupy two different sites. 27Al and 11B signals in two-dimensional hyper?ne sublevel correlation spectra were observed in the (+, +) quadrant, indicating that both 27Al and 11B are located in the second or higher order Nd3+ coordination shell. In addition, the fraction of the 11B nucleus present in the Nd3+ coordination sphere increased with an increase in the amount of B2O3. The continuous changes in the hypersensitive transition intensity and luminescence properties are strong indicators for the change in the Nd3+ coordination environment.
关键词： 2D-HYSCORE,EPR,rare-earth ion local environment,borate aluminum glass
更新于2025-09-10 09:29:36