Hydroxyphenyl-Pyridine Beryllium, Aluminum And Boron Compounds As Highly Efficient Blue And White Organic Electroluminescent Materials

Electroluminescent devices based on organic materials are of considerableinterest owing to their attractive characteristics and potential applications to flatpanel displays as well as from the standpoint of scientific interest, because of lowvoltage driving, high brightness, capability of multicolour emission by theselection of emitting materials and easy fabrication of large-area and thin-filmdevices. Small molecular materials are described with emphasis on their materialissues pertaining to charge transport, color, and luminance efficiencies. In thisthesis, we study the synthesis of white and blue EL materials, the effect to carriermobility of the intermolecular π—π interaction and the fabrication andperfomance characteristics of the highly efficient white and blue OLEDs. Five ligands: bis[2-(2-hydroxyphenyl)pyridine] (PPH), bis(2-(2-hydroxyphenyl)-4-methyl-pyridine) (4-mPPH), bis(2-(2-hydroxyphenyl)-5-methyl-pyridine) (5-mPPH), 1,6-bis(2-hydroxy-phenyl)pyridine (dppy), 1,6-bis(2-hydroxy-5-methylphenyl)pyridine (mdppy)have been synthesized and tens of complexes can be obtained such as BePP2,Be(4-mPP)2, Be(5-mPP)2, (dppy)3Al2 and dppyBF, mdppyBF by chelating Be2+,Al3+and B3+ ions with the ligands above. All of the complexes exhibited strongblue PL emisson in solution and solid state. After being purificated with chemistry ３method and sublimated, these materials achieved the high purity (> 99.99 %) tosuit the fabrication level of OLEDs. In contrast to inorganic materials, organic materials are based on independentmolecules and characterized by weak intermolecular interactions. Therefore,designs of organic materials can be readily performed of the molecular levelpreviously. In particular, organic π-electron systems and the intermolecular π—πinteraction have received attention as optoelectronic materials. When theseorganic materials are used in OLEDs, they are normally in the form of thin films.So we performed studies of the connection between the materials carrier mobilityperformance and the stacking of materials molecular in solid state. Through agreat deal of analysis of single crystal structure for the chelate complexes above,the fact can be found that the materials with high EL performance such as BePP2,Be(5-mPP)2 and dppyBF have the strong intermolecular π—π interaction in thesingle crystal structure. So a conclusion can be obtained that the strongintermolecular π—π interaction of organic molecular is a key effect factor thatmake organic materials have excellent carrier mobility ability. We demonstrated efficient organic blue light-emitting devices, using N, N′-diphenyl-N, N ′ -bis(1-naphthyl)-(1,1 ′ -biphenyl)-4,4 ′ -diamine (NPB) ashole-transporting layer, bis(2-(2-hydroxyphenyl)-pyridine)beryllium (BePP2),bis(2-(2-hydroxyphenyl)-4-methyl-pyridine)beryllium (Be(4-mPP)2) andbis(2-(2-hydroxyphenyl)-5-methyl-pyridine)beryllium (Be(5-mPP)2) complexesas the emitting layer and the electron-transporting layer respectively. All of the ELdevices fabricated with the complexes above showed very high performance,especially for their more pure blue emission. The devices exhibited the maximumluminance more than 15000 cd/m2 and high efficiency more than 15 cd/A. Incontrast to the other two beryllium complexes, the Commisson InternationaleDeL' Eclairage (CIE) color coordinate of Be(4-mPP)2 lie in (0.14, 0.08), which isclosest to the NTSC standard blue, and (dppy)3Al2 showed good stability at high ４temperature(>300°). This excellent device performance was enabled by theintroduction of very simple structure. On the other hand, we used the nocompleted energy transfer from the high efficient blue material BePP2 to theorange-red dye DCM to fabricate a high efficiency white device. In the dopedlayer, both of two...