Photoredox Properties of Iron(III) Fluoro Complexes Containing Tetradentate Open-Chain N2O2Ligands

Tetradentate open-chain Schiff base N₂O₂-ligands of acacen, benacen or salen type and fluoride anions F^? coordinate to the iron(III) central atom in methanol forming the complexes [Fe(N₂O₂)(CH₃OH)F]. The complexes do not undergo spontaneous redox changes when kept in the dark. Their irradiation into intraligand or ligand-to-metal charge transfer bands causes the photoreduction of Fe(III) to Fe(II) associated with oxidation of metanol to its radical CH₂OH. The final products of the primary photoredox and secondary dark redox processes, Fe(II) and CH₂O, are formed in a 2:1 molar ratio. The efficiency of the axial methanol ligand photooxidation is strongly wavelength dependent and influenced by the peripheral groups R of the tetradentate ligands     

Tuning Electron-Withdrawing Strength on Phenothiazine Derivatives: Achieving 100 % Photoluminescence Quantum Yield by NO2 Substitution

The weak fluorescence (quantum yield <1 % in cyclohexane) of phenothiazine ( PTZ ) impedes its further application. In addition, the nitro group (NO₂) is a well-known fluorescence quencher. Interestingly, we obtained a highly fluorescent chromophore by combining these two moieties, forming 3-nitrophenothiazine ( PTZ-NO₂ ). For comparison, a series of PTZ derivatives bearing electron-withdrawing groups (EWGs; CN and CHO) or electron-donating groups (EDGs; OMe) at the 3-position have been designed and synthesized. The phenothiazines bearing EWGs exhibited enhanced emission compared with the parent PTZ or EDG derivatives. Computational approaches unveiled that for PTZ and PTZ-OMe , the transitions are from HOMOs dominated by π orbitals to LUMOs of mixed sulfur nonbonding–π* orbitals, and hence are partially forbidden. In contrast, the EWGs lower the energy level of the lone-pair electrons on the sulfur atom, thereby suppressing the mixing of the nonbonding orbital with the π* orbital in the LUMO, such that the allowed ππ* transition becomes dominant. This work thus demonstrates a judicious chemical design to fine-tune the transition character in PTZ analogues, with PTZ-NO₂ attaining 100 % emission quantum yields in nonpolar solvent.     

Charge division mechanism in low energy binary fission and the passage of prompt fragments towards theβ-stable products in terms of the double core model

The postulates of the double core model of binary fission are examined against the two well-known charge division mechanisms of fission, namelyucd andecd. An analytic expression of the modifieducd formula is obtained. Radiochemical distribution of mass and charge, formulated from the model, is found to agree satisfactorily with available experimental results. Finally, the most probable charge and mass values of the radiochemical heavy and light products, the average number of neutron andβ-emissions per fragment, are calculated, and found to agree with experimental observations.     

Yields and energy spectra of light charged particles emitted in neutron induced fission of235U

The yields and energy spectra of light charged particles emitted in the fission of²³⁵U have been measured in the neutron energy range of 100 keV to 1 MeV. The yield of long range alpha particles is found to increase around 200 keV neutron energy compared to thermal fission. A low energy component observed in the energy spectrum was assigned to the tritons emitted in fission. The yield of this triton component is seen to have a marked increase around 500 keV. These results indicate that LCP yield is influenced by the transition state level characteristics.     

两级生产与需求不确定的供应链收益共享契约机制

研究原材料生产、产成品生产以及市场需求不确定下供应链收益共享契约机制.分析了独立无协调决策下,供应链系统的生产与订购决策.构建了收益分享协调契约与模型,研究了收益分享契约下供应链收益分配模型与机制,最后进行了算例分析.研究表明,收益共享协调机制可以减少两级生产与需求不确定性对供应链的影响,使得基于收益共享的供应链利润达到了集中决策供应链的利润水平.     

Time-Dependent Differential and Integral Quantum Yields for Wavelength-Dependent [4+4] Photocycloadditions

The [4+4] photocycloaddition of anthracene is one of most relevant photoreactions and is widely applied in materials science, as it allows to remote-control soft matter material properties by irradiation. However, highly energetic UV irradiation is commonly applied, which limits its application. Herein, the wavelength dependence of the photodimerization of anthracene is assessed for the first time, revealing that the reaction is induced just as effectively with mild visible light (410 nm). To fully establish [4+4] cycloadditions within defined chemical environments, a conceptual framework for the solution kinetics of the photo-dimerization up to long reaction times is established by developing a novel photoreaction rate law that is dependent on individual rate coefficients of the key reaction steps. These coefficients can be determined based on low conversion photochemical experiments. Both differential and integral quantum yields can subsequently be predicted that are strongly time-dependent, highlighting the need for a detailed reaction pathway analysis. The presented approach simplifies a complex photochemical scenario, making the photochemical anthracene dimerization, or potentially any other photochemical dimerization, amenable to a time-dependent understanding at the elementary reaction level.     

厚靶D（d,n）^3He反应加速器中子源的产额、能谱和角分布

给出一种计算氘钛厚靶D(d,n)3He反应加速器中子源的产额、能谱和角分布的方法,并发展了一个计算机模拟程序,程序能够计算氘束流能量小于1.0 MeV的中子源的产额、能谱和角分布.计算时使用推荐的D(d,n)3He反应截面数据和来自SRIM-2003程序的氘在氘钛靶中的阻止本领数据.给出一些典型计算结果,包括中子积分产额、中子能谱和角分布.     

Investigation of the Photochemistry and Quantum Yields of Triazines Using Polychromatic Irradiation and UV-Spectros Copy as Analytical Tool

Abstract

Photochemical reactions of atrazine, propazine, simazine, terbuthylazine, ametryn and atraton were investigated in aqueous and buffered (pH=7–9) solutions (containing a few percent of acetonitrile) using a polychromatic Xe light source at T=22[ddot]C. For terbuthylazine the photochemistry is investigated in detail, including solvent-, temperature-and pH-dependence and products found. The role of polychromatic light sources used in investigations of the photochemistry of triazines is discussed.

For the first time, quantum yield measurements were performed in the UV-band between 240–300 nm of the chlorotriazines and ametryn. Isosbestic points were found in the UV-spectra at different irradiation times, and UV-spectroscopy was used to obtain kinetic information.

Quantum yields in aqueous solutions at T=22[ddot]C for the chlorotriazines (Φ=0.048–0.062) and for ametryn (Φ=0.043) are comparable. The temperature dependence of the photoreaction of terbuthylazine leads to an activation energy of about 13 kJ mol^?1. Quantum yields in acetonitrile and hexane for terbuthylazine are about half of the values found in aqueous solution.

Atraton was not degradable under the conditions used, and the quantum yield could only be estimated to be Φ < 0.002.     

The synthesis and photophysical properties of novel cationic tetra pyridiloxy substituted aluminium, silicon and titanium phthalocyanines in water

This work reports on the synthesis, characterisation and photophysical properties of new unquaternized β-2,(3)-tetra-(2 pyridiloxy) aluminium(III) (3a), silicon(IV) (3b), titanium(IV) (3c) phthalocyanines and their water-soluble quaternized counterparts, 4a, 4b and 4c, respectively. The water-soluble silicon(IV) (4b) and titanium(IV) (4c) phthalocyanine derivatives were found to be aggregated in aqueous media but were partially or fully disaggregated in the presence of a surfactant Cremophor^® EL (CEL). The photophysical properties of aggregated complexes were investigated both in the presence of CEL and in pH 11 alone. Low triplet and fluorescence yield were obtained in pH 11 but an improvement was achieved upon addition of CEL for the aggregated complexes. The unquaternized silicon(IV) phthalocyanine complex (3b) gave the highest triplet quantum yield of 0.77 in DMF followed by its quaternized derivative (4b) with triplet yield of 0.73 in pH 11 plus CEL. The highest triplet lifetime of 220 μs was obtained for 4b in the presence of CEL. Higher fluorescence yields of 0.23 were obtained for quaternized water-soluble aluminium(III) phthalocyanine derivative (4a) in the presence of CEL.     

替位杂质对低能Pt原子与Pt(111)表面相互作用影响的分子动力学模拟

采用嵌入原子方法的原子间相互作用势，通过分子动力学方法模拟了低能Pt原子与Cu，Ag，Au，Ni，Pd替位掺杂Pt(111)表面的相互作用过程，系统研究了替位原子对表面吸附原子产额、溅射产额和空位缺陷产额的影响规律，分析了低能沉积过程中沉积原子与基体表面的相互作用机理以及替位原子的作用及其影响规律.研究结果显示：替位原子的存在不仅影响着沉积能量较低时的表面吸附原子的产额与空间分布，而且对沉积能量较高时的低能表面溅射过程和基体表面空位的形成产生重要影响.替位原子导致的表面吸附原子产额、表面原子溅射以及空位形 关键词： 分子动力学 低能粒子 替位掺杂 表面原子产额 溅射 空位