Theoretical Studies On Photophysical Propertyand The Structure Of The Iriduum Complexes

Organic light-emitting diode (OLEDs) have drawn tremendous research interestfrom both academia and industry because of their unique features and potentialapplications in display and the solid-state lighting. The phosphorescenct materialshave potential application as the emitting layer of OLED because of their highquantum efficiency and easy tuning of emission colors by changing chemicalstructrues of ligands. In this thesis, the phosphorescenct materials has a rapiddevelopment, especially the luminescent properties of the transition metal complexessuch as Iridium. But compared with green and red light-emitting materials, the bluecounterparts behave relatively inferior performance in terms of color purity,luminousefficiency and durability. So this paper is establish the relationship between molecularstructure and the properties by analyzing the emission spectrum, the radiative andnon-radiative decay rates of molecules based on the quantum chemistry calculatedresults.By using the home made program for the spectrum and radiative rates,we firstlypresent a theoretical study of the photo-physical property of the fac-Ir(ppy)3andfac-Ir(F2ppy)3, include the emission spectrum, radiative decay rate,non-radiative decayrate, phosphorescence efficiency and the lifetime.The results indicated that: theIr(F2ppy)3can reduce the energy of the HOMO, thereby leading to blueshiftedemission. Through the frontier molecular orbitals,we can find that the S0�'T1transition constitutes a charge transfer from the metal orbital to the ligand and theintraligand π�'π*transitions; with the increasing temperature, the radiative decay rateshow a slightly decreasing tendency and the non-radiative decay rate is significantlyincreased. For fac-Ir(F2ppy)3, the main channels for non-radiatively dissipating theelectronic excited-state energy are found to be the stretching vibrations of carbon andcarbon bonds, such as C5-C46linking the fluorophenyl and pyridyl rings, C43-C44ofpyridyl ring, and C42-C47of fuorophenyl ring in L1ligand. For fac-Ir(ppy)3, the largereorganization energy come from change of the bond length,especially the C5-C56、C2-C5and N55-N56. This points out the direction for further increasing thelight-emitting efficiency through suppressing these motions.Secondly, we investigate the quantitatively the photophysical properties, including emission spectra, the radiative and nonradiative decay rates of a series ofcyclometaled Ir(III) complexes (ppz)2Ir(ppy),(F2ppz)2Ir(F2ppy) and Ir(F2ppz)3withemission energies ranging from the green to blue from first-principles. Theintroduction of F and N subtitutions induces the occurance of�'*with largerenergy gap, which results in the blue shift of the emission. By detailed analysis for therelationship between the nonradiative decay rate and the important parameters, weknow that the nonradiative decay rate is very sensitive to the vibronic couplingmeasured by the organization energy. Furthermore, when the12C (or1H) is replacedby its isotope13C (or2D), involved in the nonradiative decay process, the channels tononradiatively the excited-state energy change. Then the nonradiative decay rateschange in pace, while the radiative decay rate is unchanging. This further confirm thatthe nonradiative decay process is very sensitive to the vibronic coupling. Thus, betterunderstanding of the photophysical process of the phosphors is gained, which opensthe new way to design novel and highly efficient phosphorescence materials.