Investigation On The Phosphorescent Properties Of Ir(Ⅲ) Heteroleptic Complexes And The Matching Relationship Between These Ir(Ⅲ) Complexes And The Host Materials In The OLED Device

Since1980s, OLED device has attracted enormous attention in industrialapplication and research due to the advantages of flexibility, wide-view angle, shortresponse time, high resolution and low power consumption for the flat panel displaysas well as the advantages of transparence, no flashing, small thermal effect, sunlightsimulating in the lighting.This thesis combines the quantum chemistry and quantum mechanics, and theninvestigates the relationship between the photophysical properties and structures froma theoretical point. We hope our investigation could provide guidance for the designof the high phosphorescent materials. The thesis mainly divides into two parts：The first parts: The phosphorescent efficiencies of the Ir(III) carbene complexes1-3with wide-range color tuning were focused on in this work. A DFT/TDDFT(Density functional theory/Time-dependent density functional theory) investigation onthe geometries in the ground and lowest triplet excited states, the frontier molecularorbitals, the absorption spectra and d-orbital splittings of1-3were provided to get abetter understanding of structure-property relationships. Importantly, to shed light onthe difference in phosphorescent quantum yields for1-3, the radiative decay constantsas well as zero-field-splitting parameters were calculated based on the estimation ofspin-orbit coupling (SOC) matrix elements denoted asT1H SOC Sn. The results showthat for any complex, the radiative decay rates in the three substates (namely, Tx, Tyand Tz) are not equal, and the largest radiative rates of1-3are all located in xsubstates with the values about1.0764×104s-1,0.8231×104s-1and1.9596×104s-1,respectively. Moreover, for3with the highest quantum efficiency, we make efforts tomodify it through varying substituents and substituent-positions not only to achieveblue shift in the emission but also to obtain improved triplet energy.The second parts: A series of heteroleptic iridium(III) complexes wereinvestigated by using density functional theory/time-dependent density functionaltheory (DFT/TD-DFT) approach to determine the influence of diphenylphosphoryl(Ph2PO) moiety on the electronic structures, phosphorescent properties and theOLED performance. The results reveal that the introduction of the Ph2PO groupcould not only dramatically change the electron density distributions of LUMO and cause red shifts of the emission wavelengths, but also increase the oscillator strengthsand the metal character, thus leading to larger radiative decay rates. Additionally,compared with FIrpic, those complexes with Ph2PO substituents could improve theelectron injection/balance ability, increase the F rster energy transfer rate and confinethe triplet excitons to the guest phosphors, hence resulting in better OLEDperformance. Interestingly, further analysis indicates that compared to IrpicPO withPh2PO group sited at the phenyl ring of the phenypyridine (ppy) ligands, IrpicPOpywith Ph2PO group sited at the pyridine ring of the ppy ligands performs better in thehole trapping and hole injection ability. Finally, we hope our investigations wouldfacilitate the future design of high efficient phosphorescent materials.