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Denis Y. Kondakov Thomas D. Pawlik William F. Nichols William C. Lenhart 《Journal of the Society for Information Display》2008,16(1):37-46
Abstract— Based on the observed changes in chemical compositions of fluorescent and phosphorescent carbazole‐based OLEDs during operation, a free‐radical mechanism of operational degradation is proposed. Chemical analysis and identification of low molecular weight and oligomeric products, device physics, photochemistry, and electron paramagnetic resonance (EPR) studies point to the excited‐state homolytic‐bond dissociation followed by radical additions as key mechanism steps. Comparable bond dissociation energy and singlet excited‐state energy result in a relatively fast degradation process of carbazole‐based OLEDs. OLED operation leads to the accumulation of solid‐matrix‐trapped long‐lived π‐radical species in their charged or neutral forms, acting as non‐radiative recombination centers and luminescence quenchers. The proposed free‐radicals‐mediated degradation mechanism could be a common degradation mechanism affecting a wide range of OLED compositions and structures. In the framework of this mechanism, the relationship between the excited‐state energy and the weakest bond dissociation energy of OLED materials is of the fundamental importance for the operational stability of OLED devices. 相似文献
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采用基于密度泛函理论的量子化学方法研究了催化重整过程中正庚烷脱氢生成烯烃的反应过程。结果表明,在无催化剂作用下,正庚烷分子的仲碳C-H键优先发生均裂,生成烷基自由基和氢自由基,均裂能在433.80~434.83 kJ/mol范围;中间产物烷基自由基中,与自由基碳相邻的仲碳位的C-H键容易发生均裂生成烯烃,均裂能在187.11~209.18 kJ/mol范围。正庚烷脱氢反应产物主要为2-庚烯和3-庚烯。在Pt催化剂作用下,正庚烷均裂仲碳位C-H键的反应能垒在75.90~78.51 kJ/mol范围,中间产物烷基自由基中,与自由基碳相邻的仲碳位的C-H键均裂的反应能垒为99.63 kJ/mol,说明Pt催化剂有效地降低了烷烃脱氢反应能垒。
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Haynes RK Wong HN Lee KW Lung CM Shek LY Williams ID Croft SL Vivas L Rattray L Stewart L Wong VK Ko BC 《ChemMedChem》2007,2(10):1464-1479
As the clinically used artemisinins do not withstand the thermal stress testing required to evaluate shelf life for storage in tropical countries where malaria is prevalent, there is a need to develop thermally more robust artemisinin derivatives. Herein we describe the attachment of electron-withdrawing arene- and alkanesulfonyl and -carbonyl groups to the nitrogen atom of the readily accessible Ziffer 11-azaartemisinin to provide the corresponding N-sulfonyl- and -carbonylazaartemisinins. Two acylurea analogues were also prepared by treatment of the 11-azaartemisinin with arylisocyanates. Several of the N-sulfonylazaartemisinins have melting points above 200 degrees C and possess substantially greater thermal stabilities than the artemisinins in current clinical use, with the antimalarial activities of several of the arylsulfonyl derivatives being similar to that of artesunate against the drug-sensitive 3D7 clone of the NF54 isolate and the multidrug-resistant K1 strain of P. falciparum. The compounds possess relatively low cytotoxicities. The carbonyl derivatives are less crystalline than the N-sulfonyl derivatives, but are generally more active as antimalarials. The N-nitroarylcarbonyl and arylurea derivatives possess sub-ng ml(-1) activities. Although several of the azaartemisinins possess log P values below 3.5, the compounds have poor aqueous solubility (<1 mg L(-1) at pH 7). The greatly enhanced thermal stability of our artemisinins suggests that strategic incorporation of electron-withdrawing polar groups into both new artemisinin derivatives and totally synthetic trioxanes or trioxolanes may assist in the generation of practical new antimalarial drugs which will be stable to storage conditions in the field, while retaining favorable physicochemical properties. 相似文献
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