两个基于氢键构筑的超分子镁配合物的合成、 晶体结构及荧光性质

以5,6-苯并咪唑二酸(H₃bidc)为有机配体, 在水热条件下通过控制反应温度得到了2个镁配合物[Mg(Hbidc)(H₂O)₄](1) 和 [Mg(Hbidc)(H₂O)₅]·4H₂O(2). 通过单晶及粉末X 射线衍射、 红外光谱、 元素分析和热重分析对配合物进行了表征. 结果表明, 配合物1和2均为单核分子, 分别以不同的堆积方式通过氢键构筑成三维超分子结构. 值得注意的是, 配合物2的结构中捕获了由氢键连接的环状四聚体水簇(H₂O)₄. 配合物1和2的电荷布居分析结果与晶体结构的讨论一致. 此外, 固体荧光分析表明, 配合物1和2在室温下具有较强的蓝光发射.     

Lifetime prediction of ABS polymers based on thermoanalytical data

The service life of ABS polymer, stabilized by 2-(3,5-di-tert-butyl-4-hydroxyanilino)-4,6-bis(octylthio)-1,3,5-triazine and containing 50% of a modifying rubber component, was estimated from oxidative induction times measured by DSC in isothermal mode in the temperature interval 140–170°C. The lifetime of ABS powder at the actual temperature of drying was predicted by linear extrapolation according to Arrhenius. However, the extrapolated value was much longer than the real lifetime determined from the long-term oven aging tests at 70 and 90°C, simulating the industrial drying process. The effect of changes in the apparent activation energy of oxidation due to antioxidant consumption during polymer aging is discussed.     

卤化银乳剂颗粒上不对称菁染料J-聚体荧光的研究

光谱增感机理的研究是感光科学中的一个重要课题Gilman^[1]和Kuhn等^[2]曾经提出光谱增感的电子转移和能量传递理论。随着现代谱学手段的出现,为人们了解光谱增感的初始过程提供了条件。近年来,电子转移的机理已被广泛接受,并用来解释与光谱增感有关的各种现象。但在ns~ps范围内的光谱增感动力学方面的研究还不多见。Dahne认为光谱增感不仅决定于染料与卤化银的能级关系,而且是由动力学控制的^[3],激发态染料向卤化银导带注人电子的电子转移过程与辐射及其他无辐射去活过程是竞争的^[4]我们通过对两种不对称的苯并咪哇唾碳著染料在AgBrI乳剂颗粒上吸附形成的J一聚体的荧光性质的研究,以求深人了解光谱增感的电子转移机理及其动力学过程,无疑是有重要意义的。     

Free volumes in polystyrene probed by positron annihilation

Free volume characteristics in three samples of monodisperse polystyrene were investigated by positron annihilation technique over a temperature range from 300 to 380 K. The number-average molecular weight of the samples ranged from 5730 to 1,524,000. The observed lifetime spectra were resolved into three components, where the longest lifetime, τ₃ was associated with the pick-off annihilation of ortho-positronium (o-Ps) trapped by free volumes. The change of the temperature coefficient of τ₃ was observed at around 350 K, at which the value of τ₃ was a constant value of 2,3 ns for all specimens with different molecular weights. There was no discrete change of τ₃ in intensity, which is corresponding to the number of free volumes. The size of free volume at glass transition was evaluated to be 0.l nm³. © 1996 John Wiley & Sons, Inc.     

钆铁磁－顺磁相变的正电子寿命研究

通过测量金属钆在居里点附近的正电子湮没寿命谱随温度变化的关系，发现钆的正电子湮没寿命在居里点近邻Ｔ＜ＴＣ一侧随温度有显著变化，而在此温区以外几乎不随温度变化     

Free volume‐size dependence on temperature and average molecular‐weight in poly(ethylene oxide) determined by positron annihilation lifetime spectroscopy

Positron lifetime measurements were carried out in a series of poly(ethylene oxide)—PEO—of different average molecular weights (M _w): 1000, 1500, 6000, 10,000, 300,000, and 4 M. The mean radius (R ) and the mean free volume size (V_f) values were determined using a semiempirical equation that correlates the ortho‐positronium (o‐Ps) lifetime (τ₃) and size of holes existing in the amorphous phases. The hole mean radius values determined at room temperature from lifetime spectra were found to be between 2.68 and 2.97 Å, and the hole volumes between 80 and 110 ų. Free volume size evolution was studied with temperature variation until the melting temperature of the PEO samples. The degree of crystallinity and the melting temperatures were determined by Differential Scanning Calorimetry. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 219–226, 1999     

Excited-State dynamics of conjugated polycarbosilane oligomers with branched dimethyl or diphenyl group

Dimethyl or diphenyl branched conjugated polycarbosilane oligomers in solutions, including poly[[1,4-bis(thiophenyl)buta-1,3-diyne]-alt-(dimethylsilane)], poly[[1,4-bis(thiophenyl)buta-1,3-diyne]-alt-(diphenylsilane)], poly[[1,4-bis(phenyl)buta-1,3-diyne]-alt-(dimethylsilane)], and poly[[1,4-bis(phenyl)buta-1,3-diyne]-alt-(diphenylsilane)], were investigated by steady-state and picosecond time-resolved spectroscopies to elucidate the effect of silicon-atom introduction into the π-conjugated copolymer backbone and the substitution of the aromatic phenyl group on the silicon atom. The introduction of silicon atoms into π-conjugated copolymer backbones induces slow decay emission components with lifetimes of about 450 ps in addition to π–π* local excited-state relaxations in the time-resolved fluorescence decay profiles. The diphenyls, which are branched in the silicon atoms, bring about broad, structureless emission bands in the low-frequency region of the steady-state fluorescence spectra. However, such broad bands do not occur in the case of dimethyl branched conjugated polycarbosilane oligomers. The time-resolved and solvent-dependent studies of these bands imply that the excited-state dynamics of diphenyl branched conjugated polycarbosilane oligomers can be related to an intramolecular charge-transfer dynamics through an inductive and (d-p) π-conjugation effect between the π-conjugated backbone and the branched phenyl ring. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2901–2908, 1999     

Average Arrival Time: an Alternative Approach for Studying Fluorescent Behavior of Single Quantum Dots?

Due to photoluminescence intermittency of single colloidal quantum dots (QDs), the traditional exponential fluorescence lifetime analysis is not perfect to characterize QDs' fluorescent emission behavior. In this work we used the time-tagged time-resolved (TTTR) mode to record the fluorescent photons from single QDs. We showed that this method is compatible with the traditional lifetime analysis. In addition, by constructing the trajectory over time and the distribution of average arrival time (AAT) of the fluorescent photons, more details about the emission behavior of QDs were revealed.     

Carrier dynamics in CsPbI3 perovskite microcrystals synthesized in solution phase

Carrier diffusion and recombination kinetics in all-inorganic CsPbI₃ perovskite microcrystals directly synthesized in solution phase are reported.