Design,Synthesis And Eletroluminescene Properties Of Platinum(?) Complexes And Host Materials

Since organic light-emitting device was invented by C.W.Tang and S.A.Van Slyke in 1987,it has attracted much attention from industrial and the scientific community.Much progress has been achieved in O LEDs solid-state lighting and display over the past three decades.Generally host and guest doping system is applied for OLEDs fabrication.So in this thesis,our research interest mainly focuses on the design and synthesis of different functional organic small molecule materials as high efficiency guest materials and host materials.The photophysical and electroluminescence properties of these materials were systematically investigated.In chapter 2,a series of tetradentate cyclometalated platinum(?)complexes(Pt 1,Pt 2 and Pt 3)based on 2-phenylbenzimidazole-containing ligands have been prepared,and their photophysical properties were investigated.Due to the robustness of the coordination framework,these Pt(?)complexes exhibited excellent thermal stabilities with the decomposition temperature above 400 ?.The 2-phenylbenzimidazole motif was functionalized with twisted aryl gro up,which discouraged the intimate intermolecular interaction,thus leading to constant CIE coordinates at different doping ratios.The effect of replacement of coordinating pyridine group by thiazole and oxazole on the photophysical properties,electroche mical behaviors and electroluminescence performance have been studied.Single crystal X-ray diffraction analyses of Pt 1 revealed the weak intra-molecular interaction,particularly negligible Pt···Pt interaction,in the solid state,which was consistent with its electroluminescence properties at high doping level.OLEDs based on these Pt(?)complexes were fabricated with typical multiple layered device configuration.Among the three Pt(?)complexes,the pyridine-based Pt 1 compound showed the highest elec troluminescence performance with the maximum external quantum efficiency of 22.3%.In chapter 3,four naphthalene-based host materials(PO Z,POT,3CZ and 9CZ)were designed and synthesized,where one electron-donating group and one electron-withdrawing group were covalently linked to the 1,8-positions of each naphthalene unit,respectively.Single crystal X-ray diffraction analyses of the four hosts revealed that the host molecules are held together by intensive non-covalent interactions such as ??? and hydrogen bonding interaction at solid state,which can facilitate carrier transport and migration of excitons and improve the ability of thin film formation.Red phosphorescent organic light-emitting diodes(PHOLEDs)based on these host materials with Ir(MDQ)2(acac)as dopant were fabricated and exhibited excellent device performance at low doping concentrations of 1-2 wt% due to the efficient energy transfer and reduced concentration quenching.Remarkably,POT based OLEDs at the doping ratio of 1 wt% achieved a maximum efficiency of 39.5 cd/A and 20.3% with Commission Internationale de l'Eclairage(CIE)coordinates of(0.60,0.40)without an external out-coupling structure.This result is comparable to the best red PHOLEDs with such a low doping ratio,indica ting their potential utility as a host for cost-effective and highly efficient red PHOLEDs.