Polyfluorene presenting dipolar pendent groups and its application to electroluminescent devices

We have synthesized a blue-light-emitting polyfluorene derivative (PF-TPAOXD) that presents sterically hindered, dipolar pendent groups functionalized at the C-9 positions of alternating fluorene units. The incorporation of the dipolar side chains, each comprising an electron-rich triphenylamine group and an electron-deficient oxadiazole group connected through a π-conjugated bridge, endows the resultant polymer with higher highest occupied molecular orbital and lower lowest unoccupied molecular orbital energy levels, which, consequently, lead to an increase in both hole and electron affinities. An electroluminescent device incorporating this polymer as the emitting layer exhibited a stable blue emission with a maximum brightness of 2080 cd/m² at 12 V and a maximum external quantum efficiency of 1.4% at a brightness of 137 cd/m². Furthermore, atomic force microscopy measurements indicated that the dipolar nature of PF-TPAOXD, in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment allowing the polar organometallic triplet dopant to be dispersed homogeneously. We also fabricated an electrophosphorescent device incorporating PF-TPAOXD as the host material doped with a red-emitting osmium complex to realize red electroluminescence with Commission Internationale de l'Eclairage color coordinates of (0.66, 0.34). The resulting device exhibited a maximum external quantum efficiency of 7.3% at a brightness of 1747 cd/m² and a maximum brightness of 7244 cd/m². © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2073–2084, 2007     

Synthesis and crystal structure of nickel(Ⅱ) and zinc(Ⅱ) complexes with 2,4-bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine

2,4-Bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine(bpt) has been synthesized by using a new, simple and general method with high yields. Reactions of bpt with Ni(CIO4)2 · 6H2O and Zn(CIO4)2 · 6H2O in methanol gave mononuclear complex [Ni(bpt)2] · (CIO4)2 · H2O and ternary complex [Zn(mpt)2(dmp)](CIO4)2 respectively, where mpt (2,4-dimethoxy-6-(3,5-dimethyl-pyrazol-1-yl)-1,3,5-triazine) and dmp(3,5-dimethylpyrazole) are the alcoholysis products of bpt in the presence of Zn2+ ion. A possible mechanism for this catalytic reaction was proposed. X-ray crystal structure for ligand bpt, Ni and Zn complexes are reported. The protonated form of the ligand bpt crystallizes as its perchlorate salt including one molecule of water, [Hbpt · H2O · CIO4]. The proton is located on one pyrazole N-atom. [Hbpt ?H2O ?CIO4], in which [Hbpt]+ is in cis-cis conformation, are packed in slipped stacks of approximately parallel layers. The π-π overlap interactions between the non-protonized pyrazoles of the adjace     

关于货币市场结构转换利率期限结构的实证研究

基本的利率期限结构模型均未能将结构转换效应考虑进来,因此为了探讨结构转换架构下利率期限结构模型的特性,本文在中国货币市场利率数据的基础上对基本利率期限结构模型和结构转换利率期限结构模型进行了比较研究,结果发现中国货币市场利率动态中存在明显的结构转换效应,且在结构转换效应中其本身也存在着不稳定性,这充分反映了中国货币市场在发展过程中的不成熟特征.     

Performance Study and Analysis of Parallel Multilevel Preconditioners

The significant gap between peak and realized performance of parallel systems motivates the need for performance analysis. In order to predict the performance of a class of parallel multilevel ILU preconditioner (PBILUM), we build two performance prediction models for both the preconditioner construction phase and the solution phase. These models combine theoretical features of the preconditioners with estimates on computation cost, communications overhead, etc. Experimental simulations show that our model predication based on certain reasonable assumptions is close to the simulation results. The models may be used to predict the performance of this class of parallel preconditioners.*The research work of the authors was supported in part by the U.S. National Science Foundation under grants CCR-9988165, CCR-0092532, ACR-0202934, and ACR-234270, by the U.S. Department of Energy Office of Science under grant DE-FG02-02ER45961, by the Kentucky Science & Engineering Foundation under grant KSEF-02-264-RED-002.     

Precise Supramolecular Polymerization of Liquid Crystalline Block Copolymer Initiated by Heavy Metallic Salts

Chinese Journal of Polymer Science - Heavy metallic salts are capable to bind with proteins and cause detrimental fibrilization in living cells. Herein, we report a similar case of supramolecular...     

Antioxidant and cytotoxic activity of lichens collected from Bidoup Nui Ba National Park,Vietnam

Research on Chemical Intermediates - Lichens were some of the earliest colonizers of terrestrial habitats on Earth. They represent a unique symbiont between fungi (mycobionts) and algae and/or...