Theoretical Investigation Of The Impact Of Varying Ligands On The Spectroscopic Properties And Efficiency Of Bule Phosphoresoence Lr(â…¢) Complexes

Due to the great potential in future flat-panel display technologies and nextgeneration solid-state energy-saving lighting sources, considerable attention has beenpaid to the development of organic light-emitting diodes in recent years. Becausephosphorescent materials based on transition metal complexes can harvest bothsinglet and triplet excitons, these materials can achieve100%internal quantumefficiency, however their fluorescent counterparts can not exceed a maximumquantum yield of25%. Therefore, a great deal of effort has been directed towarddeveloping highly efficient phosphorescent transition metal complexes, especially theiridium(III) complexes. In order to attain full-color display, the phosphors that canemit the three primary colors-red, green, and blue-are necessary. Highly efficientgreen-and red-emitting Ir(III) complexes have been successfully synthesized.However, there are still two major problems associated with the synthesis of true-bluephosphorescent materials: the inferior color chromaticity and the low deviceefficiency.In this paper, we mainly studied the geometrical structures, electronic structures,spectroscopic properties, and phosphorescence efficiencies of four blue-emittingiridium(III) complexes,[Ir(fpmi)2(pyim)](1),[Ir(pyim)2(fpmi)](2),[Ir(fpmi)2(fptz)](3),[Ir(tfmppz)2(pyim)](4). Complex1, which has been synthesized andcharacterized in laboratory, has a high quantum yield with30.7%, and howeverexhibits the sky-blue phosphorescence. According to what we know, the triazole has alarger HOMO-LUMO energy gap than that of imidazole, we thus anticipate thatreplacing the imidazole moiety with triazole gourp in3would lead to a bule-shiftedemission wavelength. Moreover, we designed complex2and4by changing theligands. Because the crystal data of complex1are not available, for better comparingthe reliability of there functionals, B3LYP, M062X, and CAM-B3LYP, we also carried out geometry and excitation energies calculations on5. The suitable methods andfunctionals were then applied to study properties of the three other complexes. And itturns out that complex3can be considered as a highly efficient blue-emittingIridium(III) complexes.According to the frontier molecular orbital discussion, the HOMO of1-3arecomposed of d(Ir) and π(cyclometalated ligands), and however the HOMO of4mainly resides on pyim ligand, while the LUMO of the four complexes aredominately localized on the chelating ligands. We also anticipate that the emissioncolor can be readily adjusted by substituting electron withdrawing or electrondonating groups to the pyim ligand in1. And as to the calculated absorption spectra ofthe four complexes, the corresponding absorption peaks for the complexes are foundat approximately the same positions, however the absorption intensities of their bandsdiffer largely from each other. The calculated emission wavelengths in toluene mediaof the four complexes are localized at507,512,468,513nm，respectively. Moreover,we evaluated the radiative rate constants(kr) of the four complexes and the resultsshow that3has the largest krvalue and4the smallest krvalue. In the end, we hopethat our research can provide experimenters with a guideline for fabrication of moreefficient blue phosphorescence-based OLDE dyes.