Theoretical Research The Effect Of Modification Of Ligand On The Photophysical Properties For Ir(Ⅲ) Carbene Complexes

With the rapid development of society and technology, flat panel displaytechnology and lighting displays have been widely used, which also greatlycontributed to the study of the phosphorescent emitting material. In theselight-emitting materials, phosphorescent iridium complex has received wide attentionof researchers for its excellent photophysical and photochemical properties. Heavyatom effect of these iridium complexes can effectively promote the excited singletstate to the triplet excited state transition, which significantly improved the efficiencyof the phosphorescent complexes. Furthermore, by changing its partial structures of aligand can effectively adjust the emission color of such complexes and the like.In this study, we have studied the four blue phosphorescent transition metalheterocyclic carbene complexes of trivalent iridium ground state and the geometryand electronic structure and photophysical properties of the excited state by using thelatest theory, A is synthesized blue phosphorescent complexes. Based on A, in adifferent way to the introduction of the benzene ring conjugated molecule design B-D.After the introduction of the phenyl ring wherein the auxiliary ligand B, since thesteric effect such that the conjugate is destroyed, while after the introduction of thebenzene ring in the primary ligand C, such that it becomes larger conjugated structure,but also may leading to more rigid molecules. For D, after the introduction of thebenzene ring in the main ligand, almost does not alter the original conjugatedstructure.According to our results, all minimum energy iridium complexes as well as thestrongest absorption are considered to be LLCT/MLCT charge-transfer properties of the ligand and metal, but the different ways of introducing benzene has great impactto absorption wavelength. In addition, the minimum charge transfer emittingproperties has slightly different. Moreover, when extended π conjugation is broken oris held, due to occupied and unoccupied molecular orbital of the electron densitydistribution are similar, thus emitting electron transfer properties are also resemblance,and their emission wavelength can be effectively maintained. However,a largerπ-conjugated can lead to very distinct blue shift of the emission spectrum. This can beattributed to strong interaction between the non-occupied nearly degenerate molecularorbitals. We can more fully understand the radiative decay process by assessing theeffect of the spin-orbit coupling. That is, when two spin-forbidden vertical excitedstates of the excitation energy are very close and occupy two different spin-orbitcouplings in the presence of metal d orbital interaction, inter system crossing will beenhanced and finally resulting in increased radiative decay rates. Accordingly, sincethe coupling state of the S1state and T2appeared in the molecule C, therefore itsradiation decay rate is the largest in these complexes. Further study of thenon-radiative decay rate of, C has a better molecular rigidity, and its ground state andexcited state energy level spacing is large, so the non-radiative decay rate is minimal.These results reveal a greater π-conjugated eventually lead to higher quantumefficiency and reduce the energy consumption of OLED devices, which are the aim ofour study. These studies may be able to provide some instructions about designingnew efficient blue phosphorescent emitting materials for us.