The antimalarial action of 1,2,4-trioxanes such as qinghaosu (QHS) may take place through the mechanism shown schematically: In the presence of cysteine traces of non-heme iron (FeSO(4)) may cleave the peroxy bond of QHS rapidly, and the transient carbon-centered radical can attack the sulfur ligand to form a covalent bond.
A novel deep blue-emitting Zn II complex Zn(L c ) 2 (L c -) 2-(1-(6-(9H-carbazol-9-yl)hexyl)-1H-benzo [d]imidazol-2-yl)phenolate) based on a carbazole-functionalized N^O ligand was synthesized by a modified method. Other two Zn II complexes (Znwere also prepared for comparison. The remarkable substitution effect on the photoluminescent and thermal properties of the complexes was studied. The investigation indicated an unexpected amplifying hypsochromic effect of the substituents on the emission of the complex in the solid state: the larger substituent corresponded to the larger blue shift of the emission of the complex (Zn(L c ) 2 has the shortest emission wavelength of 422 nm as the deep blue emission among these three complexes). The stronger steric effect induced by the bulky substitutions should be one of the most important factors. Among the three Zn II complexes, the temperature of decomposition of Zn(L c ) 2 is the highest at 427 °C. Cyclic voltammetry (CV) of the complexes showed that the carbazole moieties remarkably improved the hole injection ability of Zn(L c ) 2 with the HOMO energy level 0.6 eV higher than those of Zn(L a ) 2 and Zn(L b ) 2 . The good hole injection and transporting ability of Zn(L c ) 2 was further proved by its three-layer devices, in which the electroluminescent (EL) emission mainly originated from the electron-transporting Alq 3 layer. Through the four-layer devices with the hole-blocking layer, the pure blue emission of Zn(L c ) 2 at 452 nm was demonstrated. Zn(L c ) 2 seems favorable among the blue-emitting Zn II complexes with a brightness more than 2000 cd m -2 , a high efficiency stability, and an excellent EL spectra stability.
Three electrophosphorescent small molecular Ir(3+) complexes, Ir(HexPhBI)(3) 1 (HexPhBI = 1-Hexyl-2-phenyl-1H-benzo[d]imidazole), Ir(CzPhBI)(3) 2 (CzPhBI = 9-(6-(2-phenyl-1H-benzo[d]imidazol-1-yl)hexyl)-9H-carbazole), and Ir(Cz(2)PhBI)(3) 3 (Cz(2)PhBI = 9-(6-(4-(1-(6-(9H-carbazol-9-yl)hexyl)-1H-benzo[d]imidazol-2-yl)phenoxy)hexyl)-9H-carbazole), were synthesized in which 3 was designed with the structure of multiposition encapsulation. Compared to the hexyl-substituted 1, 2 and 3 end-capped with the conjugated carbazole moieties have improved thermal stability. X-ray diffraction analysis proved the amorphous state of 2 and 3. High-photoluminescent efficiencies of 3 are achieved as 72% in solution and 61% in solid. It indicates that the peripheral carbazoles not only facilitate the separation of triplet-emission cores and reduce the intermolecular aggregation but also supply a routine for the intermolecular energy transfer. Electrochemical analysis showed the more oxidation states of 3, which might be anticipated to make it superior to 1 and 2 in hole injection and transporting. The important role of the peripheral carbazole moieties in carrier injection/transporting and the optical properties of the complexes were further investigated by Gaussian simulation. A dramatic electroluminescent (EL) performance, including external quantum efficiency of nearly 6%, low turn-on voltage of 2.5 V, and high brightness over 6000 cd m(-2), from the host-free spin-coated device of 3 was achieved. The superiority of multiencapsulation in EL was proved by comparing the EL performance of 2 and 3. By making comparison between the host-free and phosphor-doping devices, it indicated that the combined modification of the aliphatic chains and functional groups in multipositions is a feasible approach to realize the high-efficiency small molecular phosphorescent materials.
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