Exciton Migration in Conjugated Dendrimers: A Joint Experimental and Theoretical Study

We report a joint experimental and theoretical investigation of exciton diffusion in phenyl‐cored thiophene dendrimers. Experimental exciton diffusion lengths of the dendrimers vary between 8 and 17 nm, increasing with the size of the dendrimer. A theoretical methodology is developed to estimate exciton diffusion lengths for conjugated small molecules in a simulated amorphous film. The theoretical approach exploits Fermi’s Golden Rule to estimate the energy transfer rates for a large ensemble of bimolecular complexes in random relative orientations. Utilization of Poisson’s equation in the evaluation of the Coulomb integral leads to very efficient calculation of excitonic couplings between the donor and the acceptor chromophores. Electronic coupling calculations with delocalized transition densities revealed efficient coupling pathways in the bulk of the material, but do not result in strong couplings between the chromophores which are calculated for more localized transition densities. The molecular structures of dendrimers seem to be playing a significant role in the magnitude of electronic coupling between chromophores. Simulated diffusion lengths correlate well with the experimental data. The chemical structure of the chromophore, the shape of the transition densities and the exciton lifetime are found to be the most important factors in determining the size of the exciton diffusion length in amorphous films of conjugated materials.     

New Photoinitiating Systems for Cationic Polymerization Acting at Near UV and Visible Range

Summary: New photoiniting systems for cationic polymerization acting at near UV and visible range are described. The applicability of acylgermanes as a new class of free radical promoters for photoinitiated cationic polymerization is demonstrated. Moreover, the use of substituted vinyl halides as source for readily oxidizable free radicals is presented. The polymerization of vinyl ethers can be initiated by the irradiation of substituted vinyl halides in the presence of Lewis acids such as zinc halide. Furthermore, possibilities for conducting cationic polymerization at visible range by using highly conjugated thiophene derivatives are demonstrated. Mechanistic aspects of all initiating systems are discussed.     

Novel polymeric potassium complex: Its synthesis,structural characterization,photoluminescence and electrochemical properties

In this paper, we obtained a novel poly(vanillinato potassium) complex (PVP) as a single crystal and characterized by analytical and spectroscopic methods. A single crystal of the PVP was obtained from the acetone solution. X-ray structural data show that crystals contain polymeric K⁺ complex of vanillin. Each potassium ion in the polymeric structure is identical and seven-coordinate, bonded to two methoxy, two phenoxy and three aldehyde oxygen atoms from four vaniline molecules. Two aldehyde oxygen atoms are bridging between potassium ions. It crystallizes in the monoclinic system, space group P2₁/c, with lattice parameters a=9.6215(10) Å, b=17.4139(19) Å, c=9.6119(10) Å, β=100.457(2)° and Z=4. Thermal properties of the PVP were investigated by TGA, DTA and DSC methods. The electrochemical properties of the complex were studied in different solvents and at various scan rates. The luminescence properties of the complex in different solvents and at different pH values have been investigated. The results show that the complex exhibits more efficient luminescence property in CH₃CN and n-butanol.     

Compton scattering of 59.5 keV gamma rays from p-Si sample in an external electric field

This study is related to Compton scattering of photons from a p-Si sample whose surface charge density distributions are changed by an external electric field. The external electric field intensity in the range 0-75 kV/m was used to change the surface charge density distributions of the sample. The sample surface perpendicular to the electric field was selected as the scattering surface. The p-Si sample was bombarded by 59.5 keV γ-photons emitting from an Am-241 point source. The Compton scattered photons at an angle of 90^o were detected by an Si(Li) detector. The Compton scattering intensity suddenly increased with the application of the electric field since the applied electric field distorts both the negatively charged scattering center (free electron, bound electron, ionized acceptor) and the positively charged scattering center (hole) and their momentum distribution in the sample. There is a good third-order polynominal relation between the Compton scattering intensity and the increasing (or decreasing) electric field intensity. The results show that the positively charged scattering centers behave like negatively charged scattering centers, but the latter are slightly more effective than the former in the Compton scattering of γ-rays from the sample in the electric field.     

对机读卡民文信息采集系统的探讨

针对当前新疆维吾尔自治区招生考务管理工作中急待解决的一个问题，即万卡通数据录入系统（ＧＤＲＳ）只能识别英文，汉文而无法识别民文的问题，设计出在无民文ＤＯＳ系统的支持下也可以采集民文信息的新方案，本项目１９９６年在自治区教委立项并研制成功，填补了新疆计算机考务管理工作的空白，在１９９７年的普通高校招生统一考试，录取工作中推广实用，效果很理想。     

A green synthesis of new 3-aryl-4-phenylsulfonyl-5-aminoisoxazoles

The present work describes a new protocol for the synthesis of 5-aminoisoxazoles using α-chlorooximes and 2-phenylsulfonyl acetonitrile via green chemistry routes. The titled 5-aminoisoxazoles 3 were further reacted with 4-nitrobenzoyl chloride to obtain 5-amidoisoxazoles with moderate yields. These heterocyclic compounds were tested in vitro MTT study to investigate inhibitive abilities to some cancer cell lines (C3a, L929, T98g and Mcf-7) and compounds 3a, 3c, 3e and 3h showed noticeable cytotoxic property against four cancer cell lines.     

Theoretical prediction of ionization/oxidation potentials in conjugated polymers

Various density functional theory (DFT) functionals and semiempirical techniques were used to predict the ionization potentials of selected conjugated polymers. Ionization potentials at infinite chain lengths were estimated using Meier fit on oligomer data. Calculated gas-phase ionization potentials with BHandH functional showed good correlation with the experimental data. The results from the semiempirical techniques do not compare as favorably as the ones obtained from DFT methods. The data fitting allowed us to estimate the size of “effective ionization length”, which spanned over 20–30 double bonds in the conjugated backbone of the polymer in question.