Novel phosphors, charge carriers and charge blockers for organic light emitting devices

The work presented here describes the development of novel phosphors, charge-carriers and charge-blockers for Organic light emitting device (OLED). The first chapter describes how these devices work and how the materials affect device properties. Chapter 2 introduces the development of a series of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) derivatives as novel charge-blockers. The BCP analogs provide improved thermal stabilities by adding asymmetric substituents to bathophenathroline. The synthetic methods and full characterization of BCP derivatives are reported in this chapter. Chapter 3 describes the research works of utilizing metal complex, i.e. ruthenium bis[poly(pyrazolyl)borate] [Ru(pz3Bpz) 2] as a new hole-transporter. Chapter 4, 5, 6 and 7 provide some insights and guideline of how to design and develop the deep blue Ir and Pt phosphors. As described in chapter 4, the syntheses of Ir complexes with bis(pyrazolyl)borates require the chloride abstraction by CF3SO3Ag before pyrazolyl-borate is added to the reaction solution. Chapter 5 discusses the photophysical properties of Ir complexes with pyrazolyl ligands. Spectroscopic analysis of Ir complexes reveals that the lowest energy excited state (T 1) is a triplet ligand-centered state (3LC) on the cyclometalating ligand admixed with 1MLCT (MLCT = metal-to-ligand charge-transfer) character. The different ancillary ligands alter the 1MLCT state energy mainly by changing the HOMO energy. Destablization of the 1MLCT state results in less 1MLCT character mixed into the T1 state, which in turn leads to an increase in the emission energy. Chapter 6 presents the synthesis and characterization of ( C^E^N)2Ir(LL'), where C^E^Nis a general abbreviation for cyclometalating ligands with a bridging group. The fact of extreme long luminescent lifetime at 77 K for most (C EN)21r(LL') complexes suggests that the spatial overlap between 1MLCT transition and 3LC transition is critical to the photophysical properties of Ir complexes. Chapter 7 describes the investigation of cyclometalated platinum (II) complexes with pyrazolyl ancillary ligands. The ancillary ligands can affect photophysical properties of cyclometalated Pt complexes, e.g. 1MLCT absorption energies, extinction coefficient of T1 transition and radiative decay rate, without changing the emission energies significantly.