Circularly Polarized Luminescent Materials Based On Chiral Iridium(?) And Platinum(?) Complexes:Design,Synthesis And Optoelectronic Properties

As a basic attribute of nature,chirality is closely related to human life.Chiral molecules are not only the basic components that maintain the normal activities and physiological processes of organisms,but also have been widely utilized in the fields of asymmetric synthesis,chiral catalysis,chiral recognition,enantiomer separation,etc.Chiral luminescent materials enabling directly emitting circularly-polarized light have attracted more and more attentions of researchers,due to their potential applications in liquid crystal display panels,3D imaging systems,information storage,non-linear optics,spintronics devices and biological probes.At present,circularly polarized light is often obtained by non-polarized light through filters,but this process is generally inefficient,expensive and cumbersome.Therefore,it is necessary to develop a series of material systems which could directly emit circularly-polarized light.Up to now,the repored circularly-polarized luminescent materials mainly include organic small molecules,polymers,supramolecular self-assemblies and liquid crystal materials.However,most materials cannnot possess the strong circularly-polarized signal and high quantum efficiency simultaneously,which is because these circularly-polarized materials mostly exhibit fluorescence emission and cannot utilize triplet excitons,and have low asymmetric factor?g?values.While for circularly-polarized luminescent materials based on transition metal complexes?Ir?III?,Pt?II?,etc.?,it could enhance the efficiency of intersystem crossing by heavy atom-induced spin-orbit coupling,and singlet and triplet excitons can be utilized simultaneously,thus theoretically achieving 100%internal quantum efficiency.Therefore,this thesis aims to develop circularly-polarized phosphorescent materials based on transition metal complexes with large asymmetry factor and high luminescence efficiency,and further explore their applications in optoelectronic devices and self-assembly behaviors.The main contents are as follows:In the second chapter,a pair of chiral phosphorescent Ir?III?complexes with 2-phenylquinoline as the main ligand were synthesized by using chiral 1,1'-bi-2-naphthol as a chiral group.The enantiomers Ir?III?complexes R1 and S1 exhibited mirror-imaged signals of circular dichroism in solution and yellow phosphorescence emission at room temperature,and their quantum efficiencies in solution are up to 21%and 33%,respectively.Furthermore,the monochromatic devices were fabricated by using the enantiomers as emitting layers.Although the efficiency of devices doped with different concentrations of enantiomers R1 and S1 was not very high,the performance can be improved by further optimizing the device structures.In particular,the electroluminescent asymmetry factors of these devices were all up to the order of magnitude of 10^-3,which is of great significance for the development of a new generation of circularly-polarized organic light-emitting diodes.In the third chapter,a pair of chiral Pt?II?complexes with chiral methylbenzylisocyanide on the backbone of Pt?N^?C^?N?Cl complex using N^?C^?N?N^?C^?N=1,3-bis?2-pyridyl?benzene?as a tridentate ligand were synthesized by one-step mild reaction.And the luminescence properties of the Pt?II?complex in solution and solid state were further investigated.The enantiomer Pt?II?complexes exhibited bright green emission with wavelength between 480 and 550 nm in dilute acetonitrile solution.While in the high concentration of acetonitrile solution,they exhibited bright orange-yellow emission with the wavelength from 480 to 600 nm,and their radiative lifetime decreased sharply with increasing concentration.No circularly polarized luminescence?CPL?signal was observed in either dilute solutions or high concentration solution.However,when the complexes are doped into polymer PMMA,the green emission from intrinsic single molecule to the red emission from excimer can be achieved by adjusting the doping ratios of Pt?II?complexes in PMMA.More importantly,the amplification of CPL signal can be achieved compared with the solution state.Furthermore,the monochrome devices were fabricated.Although the luminance is not very high,the performance of the devices can be improved by optimizing the material structure and fabrication technology of devices.Simultaneously,the amplification and reduction of the circularly-polarized signal by changing the doping concentrations of Pt?II?complexes could be realized,which is of great significance for realizing the phosphorescent materials with the switch function of the circular polarization.In the fourth chapter,a series of chiral ionic phosphorescent binuclear Pt?II?isocyanide complexes were developed by changing the length of alkyl chain on binaphthol ligand and substituting groups on 6-phenyl-2,2'-bipyridine?N^?N^?C?ligands,and their structures were characterized and photophysical properties in the aggregate state were studied in detail.These enantiomers exhibited broad red emission on thin films,and the emission wavelength blue-shifted gradually as the increase of the electron-withdrawing ability of the substituents on the N^?N^?C ligand.In the solid state,the emission spectra of these complexes exhibited different levels of bathochromic-shift,indicating that there are varying degrees of intermolecular and intramolecular?-?and Pt···Pt interaction forces.In terms of the chiral optical properties,in addition to the enantiomers R2/S2-Pt-CF₃ and R3/S3-Pt-H,other complexes showed observable CPL signals,and the asymmetry factor g_lum at the maximum emission wavelength was on the order of 10^-3.Furthermore,the self-assembly behavior of these complexes at different ratios of DMSO and water were studied,and the results indicated that the morphology eventually formed into lamellar nanostructures with the length of tens or even hundreds of microns in pure DMSO solution.And further experiments demonstrated that the morphology of the intermediate states of these complexes was only related to the aging time,but not to the solvent ratios.In addition,these chiral two-dimensional nanosheets show promising potentials in optoelectronic devices.