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81.
《中国化学快报》2020,31(11):2965-2969
In the active layer of organic solar cells (OSCs), the lifetime of triplet excitons is one of the decisive factors in the diffusion length and therefore has important impact on the power conversion efficiency of the devices. Herein, we have investigated singlet excited state relaxation dynamics and their triplet exciton lifetimes of two thiophene-coupled perylene diimides (PDI) dyads (2PDI-Th and fused-2PDI-Th), in order to provide a unique explanation in depth on their different performances in OSC devices. From the transient absorption (TA) spectra, the singlet excitons of 2PDI-Th form excimers in the time scale of 1.5 ps. Then the excimers go into the triplet state via intersystem crossing (ISC). In fused-2PDI-Th, triplet excitons are generated directly from the singlet excited excitons via the efficient ISC. Density functional theory (DFT) calculations further support the formation of excimers. DFT results indicate that 2PDI-Th exhibits an H-typed molecular configuration which is beneficial to form the excimers, while fused-2PDI-Th gives a twisted X-shaped configuration in the optimized ground and excited state. In steady-state emission spectra, 2PDI-Th shows abroad and featureless spectral characteristics of the excimers with a decay time of 840 ps, which is much shorter than those of PDI (5.5 ns) and fused-2PDI-Th (3.3 ns). The triplet lifetime (67 μs) of fused-2PDI-Th is factor of 3 longer than that of 2PDI-Th (22 μs). These results demonstrate that ring-fused structure is an efficient strategy to eliminate excimer formation and prolong the lifetime of triplet excitons, which provides a new insight for design of optoelectronic molecules for high efficiency organic solar cells. 相似文献
82.
Peter Roselt Carleen Cullinane Wayne Noonan Hassan Elsaidi Peter Eu Leonard I. Wiebe 《Molecules (Basel, Switzerland)》2020,25(23)
Vitamin E, a natural antioxidant, is of interest to scientists, health care pundits and faddists; its nutritional and biomedical attributes may be validated, anecdotal or fantasy. Vitamin E is a mixture of tocopherols (TPs) and tocotrienols (T-3s), each class having four substitutional isomers (α-, β-, γ-, δ-). Vitamin E analogues attain only low concentrations in most tissues, necessitating exacting invasive techniques for analytical research. Quantitative positron emission tomography (PET) with an F-18-labeled molecular probe would expedite access to Vitamin E’s biodistributions and pharmacokinetics via non-invasive temporal imaging. (R)-6-(3-[18F]Fluoropropoxy)-2,7,8-trimethyl-2-(4,8,12-trimethyltrideca-3,7,11-trien-1-yl)-chromane ([18F]F-γ-T-3) was prepared for this purpose. [18F]F-γ-T-3 was synthesized from γ-T-3 in two steps: (i) 1,3-di-O-tosylpropane was introduced at C6-O to form TsO-γ-T-3, and (ii) reaction of this tosylate with [18F]fluoride in DMF/K222. Non-radioactive F-γ-T-3 was synthesized by reaction of γ-T-3 with 3-fluoropropyl methanesulfonate. [18F]F-γ-T-3 biodistribution in a murine tumor model was imaged using a small-animal PET scanner. F-γ-T-3 was prepared in 61% chemical yield. [18F]F-γ-T-3 was synthesized in acceptable radiochemical yield (RCY 12%) with high radiochemical purity (>99% RCP) in 45 min. Preliminary F-18 PET images in mice showed upper abdominal accumulation with evidence of renal clearance, only low concentrations in the thorax (lung/heart) and head, and rapid clearance from blood. [18F]F-γ-T-3 shows promise as an F-18 PET tracer for detailed in vivo studies of Vitamin E. The labeling procedure provides acceptable RCY, high RCP and pertinence to all eight Vitamin E analogues. 相似文献
83.
Jae Won Chang Mohammed Bhuiyan Hsiu‐Ming Tsai Hannah J. Zhang Gang Li Shaghayegh Fathi David C. McCutcheon Lara Leoni Richard Freifelder Chin‐Tu Chen Raymond E. Moellering 《Angewandte Chemie (International ed. in English)》2020,59(35):15161-15165
Herein, we report the development of an 18F‐labeled, activity‐based small‐molecule probe targeting the cancer‐associated serine hydrolase NCEH1. We undertook a focused medicinal chemistry campaign to simultaneously preserve potent and specific NCEH1 labeling in live cells and animals, while permitting facile 18F radionuclide incorporation required for PET imaging. The resulting molecule, [18F]JW199, labels active NCEH1 in live cells at nanomolar concentrations and greater than 1000‐fold selectivity relative to other serine hydrolases. [18F]JW199 displays rapid, NCEH1‐dependent accumulation in mouse tissues. Finally, we demonstrate that [18F]JW199 labels aggressive cancer tumor cells in vivo, which uncovered localized NCEH1 activity at the leading edge of triple‐negative breast cancer tumors, suggesting roles for NCEH1 in tumor aggressiveness and metastasis. 相似文献
84.
Optical imaging plays a growing role in modern biomedical research and clinical applications due to its high sensitivity, superb spatiotemporal resolution and minimal hazards. Lanthanide‐doped nanoparticles (LDNPs), as a classical category of luminescent materials, exhibit promising photostability, near‐infrared (NIR)‐excited frequency up‐/down‐converting capabilities, emission fine‐tuning and multispectral features, which have greatly promoted the endeavors of deeper and clearer diagnostics in complex living conditions. This review focuses on the recent advances of LDNP‐based multipurpose imaging studies using upconversion, downshifting, lifetime, photoacoustic and multimodal nanoprobes in the NIR (650–1000 nm) and the second near‐infrared window (NIR‐II, 1000–1700 nm). The principle and design of various functional, activatable, multiplexing or multimodal lanthanide‐imaging nanoprobes (LINPs) as well as representative biophotonic applications are summarized in detail. In addition, the future perspectives and challenges for facilitating LINPs to clinical translations are discussed. 相似文献
85.
Time resolved spectroscopy is discussed along with the theoretical and experimental methods used to measure the fluorescence lifetimes in various laser grade organic dyes. The role of solvents and their viscosities in the fluorescence life time is also discussed. Different photophysical parameters have been obtained in rigid and non-rigid dye molecules. 相似文献
86.
《Physics and Chemistry of Liquids》2012,50(4):321-326
Abstract The optical absorption spectra of Nd3+ ion in glutamic, L-aspartic and maleic acids in UV-VIS and NIR regions have been recorded. From the spectral data thus obtained, various spectroscopic parameters are evaluated. The radiative lifetimes (γR) and branching ratios (β) for the excited states of Nd3+ ion in three acids have been computed. The relationship between the environment sensitive Judd-Ofelt parameter (ω2) and the intensities of hypersensitive level (4G5/2) is in good coincidence following the Judd-Ofelt theory. 相似文献
87.
A.P. Srivastava D. Srivastava K. Sudarshan S.K. Sharma P.K. Pujari B. Majumdar K.G. Suresh G.K. Dey 《Journal of magnetism and magnetic materials》2012
Amorphous ribbons of different thicknesses of Co64.5Fe3.5Si16B14Ni2 alloy were synthesized using the melt spinning technique by varying wheel speed. The effect of cooling rate on the ribbon thickness and their soft magnetic properties have been studied. The amorphous structure has been characterized in terms of structural free volume and medium range order (MRO) by positron annihilation spectroscopy and fluctuation electron microscopy techniques. Positron lifetime spectra of amorphous samples showed two lifetime components. The first component was found to be correlated with MRO whereas, the second lifetime component was found to be associated with nanovoid type of defects, and the second component was strongly dependent on processing conditions. It could be established that the coercivity of the amorphous samples produced by the rapid solidification technique mainly depends on the defects formed during processing rather than change induced in MRO. 相似文献
88.
Composite optical vortices in noncollinear Laguerre--Gaussian beams and their propagation in free space 下载免费PDF全文
Taking two Laguerre-Gaussian beams with topological charge 1 = ±1 as an example, this paper studies the composite optical vortices formed by two noncollinear Laguerre-Gaussian beams with different phases, amplitudes, waist widths, off-axis distances, and their propagation in free space. It is shown by detailed numerical illustrative examples that the number and location of composite vortices at the waist plane are variable by varying the relative phase β, amplitude ratio η, waist width ratio ξ, or off-axis distance ratio μ. The net topological charge lnet is not always equal to the sum lsum of charges of the two component beams. The motion, creation and annihilation of composite vortices take place in the free-space propagation, and the net charge during the propagation remains unchanged and equals to the net charge at the waist plane. 相似文献
89.
Saurabh D Rindani 《Pramana》2002,58(4):575-590
QCD corrections to order α
s
in the soft-gluon approximation to angular distributions of decay charged leptons in the process e
+
e
− → t
, followed by semileptonic decay of t
, are obtained in the esu− e
− centre-of-mass frame. As compared to distributions in the top rest frame, these have the advantage that they would allow
direct comparison with experiment without the need to reconstruct the top rest frame. The results also do not depend on the
choice of a spin quantization axis for t or t. Analytic expression for the triple distribution in the polar angle of t and polar and azimuthal angles of the lepton is obtained. Analytic expression is also derived for the distribution in the
charged-lepton polar angle. Numerical values are discussed for √s=400, 800 and 1500 GeV. 相似文献
90.
A systematic semiquantitative account of all aspects of the strong and electromagnetic interactions of all the newly discovered
hadronic states (theψ’s, theχ’s, etc.) is presented within the framework of the paracharge scheme. Extensions of ideas familiar from the SU3 classification scheme to SU4 are shown to provide an understanding of the new states seen in the decays ofψ (3.1) andψ′ (3.7), including their masses and gross decay characteristics. The decays ofψ (3.1) andψ′ (3.7) themselves are studied in some detail. Since these are of electromagnetic origin in the scheme, their electromagnetic
mixing with the resonance at 4.15 GeV (theP-state of the scheme) is important. Once this is taken into account, the resulting picture is in excellent agreement with
available data. 相似文献