Comprehending radicals,diradicals and their bondings in aggregates of imide-fused polycyclic aromatic hydrocarbons

Quantum effects such as ferromagnetism were regarded as rare in organic materials. When reduced to radical states, imide-fused polycyclic aromatic hydrocarbons (IPAHs) have shown room-temperature ferromagnetism in our recent work, to be a potential candidate as ferromagnetic semiconductor. Here, we use variational Davydov ansatz parametrized by density functional theory to investigate the structural and optical properties of IPAHs and their radicals at both molecule and aggregate levels. Our calculation reveals that hydrogen mainly gives rise to radicals and proves the formation of a mid-gap polaronic state, which is further evidenced by UV-vis absorption spectra simulations, in good agreement with experiments. The significant change of dispersion between the π–π stacking structure and planar structure implies the formation of radical–radical bonding (pancake bonding), which is revealed by simulations of NIR absorption signals and serves as the physical basis of long-range ferromagnetic orders. Absorption spectra of perylene diimide (PDI), terrylene diimide (TDI) and their radicals are also predicted.

The structures and optical properties of imide-fused polycyclic aromatic hydrocarbon radicals, which exhibit room-temperature ferromagnetism as discovered recently and the strong pancake bondings in NDI radical aggregates are investigated.     

How and when does an unusual and efficient photoredox reaction of 2-(1-hydroxyethyl) 9,10-anthraquinone occur? A combined time-resolved spectroscopic and DFT study

The photophysics and photochemical reactions of 2-(1-hydroxyethyl) 9,10-anthroquinone (2-HEAQ) were studied using femtosecond transient absorption (fs-TA), nanosecond transient absorption (ns-TA), and nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopy techniques and density functional theory (DFT) calculations. In acetonitrile, 2-HEAQ underwent efficient intersystem crossing to the triplet excited state ((2-HEAQ)(3)). A typical photoreduction reaction for aromatic ketones took place via production of a ketyl radical intermediate for 2-HEAQ in isopropanol. In water-containing solutions with pH values between 2 and 10, an unusual photoredox reaction reported by Wan and co-workers was detected and characterized. Observation of the protonated species in neutral and acidic aqueous solutions by fs-TA spectra indicated the carbonyl oxygen of (2-HEAQ)(3) was protonated initially and acted as a precursor of the photoredox reaction. The preference of the photoredox reaction to occur under moderate acidic conditions compared to neutral condition observed using ns-TR(3) spectroscopy was consistent with results from DFT calculations, which suggested protonation of the carbonyl group was the rate-determining step. Under stronger acidic conditions (pH 0), although the protonated (2-HEAQ)(3) was formed, the predominant reaction was the photohydration reaction instead of the photoredox reaction. In stronger basic solutions (pH 12), (2-HEAQ)(3) decayed with no obvious photochemical reactions detected by time-resolved spectroscopic experiments. Reaction mechanisms and key reactive intermediates for the unusual photoredox reaction were elucidated from time-resolved spectroscopy and DFT results. A brief discussion is given of when photoredox reactions may likely take place in the photochemistry of aromatic carbonyl-containing compounds and possible implications for using BP and AQ scaffolds for phototrigger compounds.     

Unraveling the Mechanism of the Photodeprotection Reaction of 8‐Bromo‐ and 8‐Chloro‐7‐hydroxyquinoline Caged Acetates

Photoremovable protecting groups (PPGs) when conjugated to biological effectors forming “caged compounds” are a powerful means to regulate the action of physiologically active messengers in vivo through 1‐photon excitation (1PE) and 2‐photon excitation (2PE). Understanding the photodeprotection mechanism is important for their physiological use. We compared the quantum efficiencies and product outcomes in different solvent and pH conditions for the photolysis reactions of (8‐chloro‐7‐hydroxyquinolin‐2‐yl)methyl acetate (CHQ‐OAc) and (8‐bromo‐7‐hydroxyquinolin‐2‐yl)methyl acetate (BHQ‐OAc), representatives of the quinoline class of phototriggers for biological use, and conducted nanosecond time‐resolved spectroscopic studies using transient emission (ns‐EM), transient absorption (ns‐TA), transient resonance Raman (ns‐TR²), and time‐resolved resonance Raman (ns‐TR³) spectroscopies. The results indicate differences in the photochemical mechanisms and product outcomes, and reveal that the triplet excited state is most likely on the pathway to the product and that dehalogenation competes with release of acetate from BHQ‐OAc, but not CHQ‐OAc. A high fluorescence quantum yield and a more efficient excited‐state proton transfer (ESPT) in CHQ‐OAc compared to BHQ‐OAc explain the lower quantum efficiency of CHQ‐OAc relative to BHQ‐OAc.     

Can diffusion-weighted imaging be used as a reliable sequence in the detection of malignant pulmonary nodules and masses?

Recent developments in diffusion-weighted magnetic resonance imaging (DWI) make it possible to image malignant tumors to provide tissue contrast based on difference with the diffusion of water molecules among tissues, which can be measured by the apparent diffusion coefficient (ADC) value. We aimed to assess the diagnostic accuracy of DWI for benign/malignant discrimination of pulmonary nodules/masses with a meta-analysis. The MEDLINE, EMBASE, Cancerlit and Cochrane Library database, from January 2001 to August 2011, were searched for studies evaluating the diagnostic accuracy of DWI for benign/malignant discrimination of pulmonary nodules. We determined sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LRP and LRN), and constructed summary receiver operating characteristic SROC) curves. Across 10 studies (545 patients), there was no evidence of publication bias (P= .22, bias=−19.19). DWI had a pooled sensitivity of 0.84 (95% CI, 0.76–0.90) and a pooled specificity of 0.84 (95% CI, 0.64–0.94). Overall, LRP was 5.3 (95% CI, 2.1–13.0) and LRN was 0.19 (95% CI, 0.12–0.30). In patients with high pretest probabilities, DWI enabled confirmation of malignant pulmonary lesion; in patients with low pretest probabilities, DWI enabled exclusion of malignant pulmonary lesion. Worst-case-scenario (pretest probability, 50%) posttest probabilities were 84% and 16% for positive and negative DWI results, respectively. Diffusion-weighted magnetic resonance imaging can be used to differentiate malignant from benign pulmonary lesions. High-quality prospective studies regarding DWI in the evaluation of pulmonary nodules are still needed to be conducted.     

A Universal Strategy for Aptamer‐Based Nanopore Sensing through Host–Guest Interactions inside α‐Hemolysin

Nanopore emerged as a powerful single‐molecule technique over the past two decades, and has shown applications in the stochastic sensing and biophysical studies of individual molecules. Here, we report a versatile strategy for nanopore sensing by employing the combination of aptamers and host–guest interactions. An aptamer is first hybridized with a DNA probe which is modified with a ferrocene?cucurbit[7]uril complex. The presence of analytes causes the aptamer–probe duplex to unwind and release the DNA probe which can quantitatively produce signature current events when translocated through an α‐hemolysin nanopore. The integrated use of magnetic beads can further lower the detection limit by approximately two to three orders of magnitude. Because aptamers have shown robust binding affinities with a wide variety of target molecules, our proposed strategy should be universally applicable for sensing different types of analytes with nanopore sensors.     

Mapping Brain Metabolites Using a Double Echo-Filter Metabolite Imaging (DEFMI) Technique

A double echo-filter metabolite imaging (DEFMI) technique was developed for spatial mapping of low-concentration metabolites in the human brain. This imaging technique simultaneously acquires two images from two individual metabolites, respectively, using conventional imaging acquisition. It provides (i) efficient water and lipid suppressions, (ii) the capability of collecting high-resolution metabolite images within a short time and creating a ratio image from two interesting metabolites within a single experiment, and (iii) flexibility and simplicity for experimental setup and data processing. The technique was examined by both phantom and human brain experiments at 4 Tesla. The results reveal that the DEFMI technique is promising for applications in metabolism studies aimed at investigating physiological and pathological questions.     

SiC衬底上β-Ga2O3薄膜生长及p-SiC/n-β-Ga2O3异质结光伏特性

本文采用脉冲激光沉积(PLD)技术在p型4H-SiC衬底上,制备出沿(403)择优生长的β-Ga₂O₃薄膜。结果表明,衬底生长温度对β-Ga₂O₃薄膜的形貌、结构、组分,以及生长机理都有重要影响。当生长温度由300 ℃升高至500 ℃时,薄膜结晶质量随生长温度升高而提高,当温度进一步升高到600 ℃时,薄膜结晶质量变差,这是由于在相对低温(500 ℃以下)阶段,生长温度越高,沉积在衬底上原子的动能越大,越容易迁移,使得β-Ga₂O₃薄膜主要按照二维生长模式进行生长,薄膜结晶质量提高,表现为随着生长温度升高,粗糙度降低。但当温度上升到600 ℃时,由于4H-SiC衬底和β-Ga₂O₃薄膜之间的热膨胀系数存在差异,导致薄膜生长由主要以二维生长模式向三维岛状演变。基于p-4H-SiC/n-β-Ga₂O₃构筑的异质结太阳电池,其标准测试条件下光电转换效率达到3.43%。     

In vivo measurement of tissue damage, oxygen saturation changes and blood flow changes after experimental traumatic brain injury in rats using susceptibility weighted imaging

Traumatic brain injury (TBI) is a prevalent disease, and many TBI patients experience disturbed cerebral blood flow (CBF) after injury. Moreover, TBI is difficult to quantify with conventional imaging modalities. In this paper, we utilized susceptibility weighted imaging (SWI) as a means to monitor functional blood oxygenation changes and to quantify CBF changes in animals after trauma. In this study using six rats, brain trauma was induced by a weight drop model and the brain was scanned over four time points: pre trauma, and 4 h, 24 h and 48 h post trauma. Five rats survived and one died after trauma. A blood phase analysis using filtered SWI phase images suggested that three rats recovered after 48 h and two rats deteriorated. SWI also suggested that CBF decreased by up to 26%. The CBF change is in agreement with the results of arterial spin labeling methods conducted in this study and with previously published results. Furthermore, SWI revealed an enlargement of the major venous vasculature in deep brain structures, in accordance with the location of diffuse axonal injury. Compared with the traditional, invasive, clinical monitoring of cerebral vascular damage and reduction in blood flow, this method offers a novel, safe and noninvasive approach to quantify changes in oxygen saturation and CBF and to visualize structural changes in blood vasculature after TBI.     

kJ级宽带低相干激光驱动装置

激光等离子体相互作用的不稳定性将有望通过降低高功率激光装置输出光束的相干性得到大幅缓解。利用低相干光源作为种子源,采用钕玻璃放大介质,研制成功国际首台kJ级大带宽低相干激光装置,实现了带宽13 nm、能量960 J、脉宽3～10 ns可调,相干时间仅为300 fs的大能量光脉冲输出。输出脉冲光谱匀滑无纵模结构,且谱相位随机分布,可实现脉冲波形和光谱分布的无关联精密调控。该装置不仅成功演示验证了低相干激光驱动器的单元技术及系统集成技术,同时也为激光等离子体相互作用及高能量密度物理研究提供了全新的实验研究平台。     

高功率钕玻璃激光系统低时间相干光频率转换技术研究进展

低时间相干脉冲可有效提高激光与等离子相互作用中参量不稳定性的阈值,但高效频率转换难题是实现其工程应用瓶颈之一。系统分析了高功率激光驱动器已有的各类低时间相干脉冲频率转换技术的特性,并基于数值模拟和实验分析了部分掺氘DKDP晶体用于超辐射光倍频、三倍频的特性与工程应用可行性,结果表明掺氘17%左右DKDP晶体可以提高钕玻璃系统超辐射光的倍频效率,理论转换效率可达到约80%,10%梯度掺氘DKDP晶体则可实现5 THz带宽三倍频输出。