Design,Synthesis And Photophysical Properties Of Azolate-based Cationic Iridium(?) Complexes

Benefiting from the ionic transition metal induced spin-orbit coupling effect, ironic transition metal complexes ?iTMCs? can harvest both singlet and triplet excitons to achieve high photoluminescent quantum yield. Among all the iTMCs, Ir??? complexes have attracted enormous interest of researchers due to their excellent photophysical properties, photo- and thermal stabilities, relatively short excited state lifetimes and facile color tunability, which makes them good candidates for the potential applications in many fields, such as electroluminescent devices, photo-catalytic water reduction, photovoltaic cell, biological images and chemosensors. The application of cationic Ir??? complexes in light-emitting electrochemical cells ?LECs? is one of the important subjects, which possesses many advantages over the traditional organic light-emitting diodes ?OLEDs? such as simple device architecture, the insensitivity to the work-function of the electrodes as well as the facile device fabrication process. However, owing to LECs'single emissive layer, their performances are largely depended on the properties of the emissive materials, requiring extraordinary photophysical properties, charge transport properties and good stabilities. Azolate-based ligands have been proved to be good building blocks for high efficiency multifunctional cationic Ir??? complexes. However, there is lack of systematic structure-properties relationship investigation. Meanwhile, to meet the demands of practical use in flat-panel displays and solid-state lighting, the exploration of more efficient emitters with all primary color especial the blue ones is of great importance.In this thesis, we describe the design, synthesis and characterization of a series of novel cationic Ir??? complexes. Together with the results obtained from density functional theory calculation, the structure-properties relationship has been revealed. The relative researches are outlined as follows:1. Towards efficient blue emission cationic Ir??? complex with azolate-type ancillary ligands. Because of their intrinsically large ?-?* energy gap, they can be used to serve as excellent moieties to construct emitters with high energy emission. When adopting ?2,4-difluro-phenyl?-1H-pyrazole ?dfppz? as cyclometalating ligand and 1,2, 4-triazole-pyridine type ancillary ligands, we successfully obtained a blue phosphor material emitting at 460 nm with high photoluminescent quantum yield ?PLQY? of 30.1% in neat film. To investigate the structure-properties relationship, we prepared some other imidazole-based cationic Ir??? complexes and investigated their photophysical and electron-transporting properties.2. Panchromatic adjustment for cationic Ir??? complexes bearing triazolate cyclometalated and ancillary ligands:synthesis, characterization and theoretical investigations. Complexes with aryl-1,2,3-trizoles type as cyclometalating ligands and 1,2,4-triazole-pyridine type as ancillary ligands individually show superior efficiency. We expect that the combining arrangement of the aforementioned triazoles ligands together with multifunctional substituent decoration may be a more effective and handy strategy to build Ir?III? complexes with high efficiency and achieve full color emissions. The prepared complexes exhibit blue ?461 nm? to red ?649 nm? emissions, with favorable PLQYs. We have investigated the electronic structures and photophysical processes of all complexes through theoretical methods. When complex 3 was adopted to fabricate single layer organic light-emitting device, greenish-blue phosphorescent device has been successfully achieved with good performance. The maximum brightness of this device is 236 cd m-2 and the peak current efficiency is 2.19 cd A^-1.