Synthesis, Characterization, Photoluminescence And Electroluminescence Studies Of Transition Metal Rhenium (Ⅰ) Complexes

Organic light-emitting devices (OLEDs) that have been realized the full-colored displays are promising candidate for next generation flat panel displays. Recently, considerable efforts in the field of organic light-emitting diodes (OLEDs) are being devoted to improving display technology such as efficiency, flexibility and long lifetimes by exploring new luminescent organic or organomettic compounds and optimizing device structure. On the other hand, it is well known that a reasonable device should have the injection and transport balance between electron and hole from the cathode and the anode, respectively , which ensure the recombination chance at the emitting layer. The application of the transition metal complexes in the OLEDs have improved greatly the luminescent efficincy because of their characteristics that can control electron transporting and energy transferring.The emission of the OLEDs based on transition metal complexes is primarily from a triplet metal-to-ligand-charge-transfer (MLCT) state and the highly efficient phosphorescent emission is attributed to the strong spin-orbit coupling due to the existence of the heavy metal. As another class of phosphorescent materials, reaschers focus on rhenium (I) complexes and their derivatives because of their virtues such as high room temperature phosphorescence quantum yield, relatively short excited state lifetime and excellent thermal, chemical, and photochemical stability. Up to date, the reports about the devices based on Re (I) complexes are few. Most of rhenium (I) complexes contain the diimine ligands and their derivatives and the neutral carbonyl ligands. The design and syntheis of other metal-containing luminophors has become another aim of many reaearch endeavors.But in fact, the ratio of electron transporting is lower than the ratio of the hole transporting. So researchers have also paid much important attention to design and synthesize new electron tronsproting materials nowadays.In this paper, we designed and synthesized a noval electron transporting material 4-(5-p-tolyl- 1, 3, 4-oxadiazol-2-yl) pyridine (PTOP). In course of ligand preparation, we broke through the traditional diimide dehydration and employed"one pot boiled"1, 3, 4-oxadiazol synthesis route, in which we made 4-pyridinevarboxylic acid and 4-methylbenzoichydrazide dissolve in new distilled POCl₃ and heated under reflux. Not only simplified reaction process but also improved yield.Then we made the new ligand coordinate with tricarbonyl diimine rhenium (I) complexes that have the formula [Re(CO)₃(N^N)(PTOP)]PF₆ (where N^N = bathophenardine, 1,10-phenanthroline, and pyrazino[2,3-f][1,10] phenanthroline-2,3-dicarbo- nitrile). The relevant chatacteriztion such as elemental analysis, ¹H NMR, IR and UV-vis absorption spectrums were studied. To study the photoluminesce and electroluminescence properties of Rhenium (I) complex, we fabricated different doping concentration devices with structure ITO/PEDOT (60nm) /Poly (N-Vinylcarba-zole)(PVK):2-(4-t-butyl)phenyl-5-bipheny-1,3,4- oxadiazol (PBD) :Re(I) complex(100:80:x)(80nm)/Ba(30nm)/Al(80nm) by spin-coating technique. The turn-on voltage, maximum efficiency, and brightness for green emission obtained from the device are 8.5V, 2.1cd/A and 165cd/m2, respectively.