Theoretical Study On The Effects Of Variation Of Main Ligand On The Electronic Structure And Photophysical Properties Of Ir(?) Complexes

After years of extensive research and continuous development,OLED have now been commercialized on a large scale and have broad application prospects.Transition metal complexes can break the transition barrier due to spin-orbit coupling(SOC).The electrons complete the intersystem crossing(ISC)process from the singlet excited state and emit phosphorescence from the triplet excited state to the ground state.Luminescent materials with high luminous efficiency,relatively low non-radiative transition rate,and tunable luminescent range have always been a research hotspot.Organometallic Ir(?)complexes are usually in an octahedral-like stereoconfiguration,with the metal atoms surrounded by cyclometallated ligands.With different cyclometalated ligands,organometallic Ir(?)complexes can realize the modulation of different phosphorescence emission wavelengths in the visible and near-infrared regions.In this paper,the structure and light absorption and emission properties of the designed Ir(?)complexes were studied by means of theoretical calculation using Gaussian09 software.The following are the main research contents:1.Theoretical insight on the effect of different positional N-substitution on the electronic structures and photophysical properties of five iridium(?)complexes bearing fluorine substituted 2,3'-bipyridine.Four new Ir(?)complexes were designed by directly replacing the carbon atom of the pyridyl group on the main ligand with nitrogen atom.They have different structures,frontier molecular orbitals and absorption and emission properties.The calculated bond parameters,absorption spectra,and emission wavelengths are in good agreement with the experimental data,which proves the rationality of the calculation process.The pyridine,pyrazine,pyrimidine and pyridazine moieties on the main ligands of the five complexes bring different electron distributions to the Ir(?)complexes due to the different positions of the substituted nitrogen atoms.This factor results in a red or blue shift of the phosphorescent emission wavelength.These above provide a way to adjust the emission wavelength of Ir(?)complexes.These above provide a way to adjust the emission wavelength of Ir(?)complexes.Among them,the complex with emission wavelength of441 nm is theoretically a potential blue OLED light-emitting material.It has the possibility of making high-performance blue phosphorescent OLEDs.2.Theoretical study on effects of modified carbazolyl Ir(?)complexes on phosphorescence emission properties.Five different Ir(?)complexes were designed by introducing electron-withdrawing groups,electron-donating groups or changing the conjugation properties of the carbazole group on the main ligand.The emission wavelengths of six complexes were obtained by TDDFT method,and the emission wavelengths were between 522-582 nm.The-Br and-CH₃groups have little effect on the phosphorescence emission wavelength of the complexes.The-OCH₃group blue-shifts the emission wavelength,which may be due to its strong electron-donor-induced effect.Destruction of the conjugation effect may blue-shift the phosphorescence emission wavelength and adversely affect ³MLCT.This can be confirmed from the absorption intensity at 350 nm of the fitted absorption spectrum.