Design,Synthesis,and Excited States Tuning Of Highly Efficient Iridium (Ⅲ) Complexes For Applications In Optoelectronics

Organic electronics,as one of the most promising research fields,has been attracting considerable attentions.Organic semiconductors,the material basis of organic electronics,have wide applications in many fields such as materials,information,energy,medical treatment,and defense owing to their various structures,easy functionalization,flexibility,easy processing,light weight and large area.Phosphorescent transition-metal complexes（PTMCs）represent important kinds of organic semiconductors.Among all kinds of PTMCs,the cyclometalated iridium（Ⅲ）complexes are considered as the most attractive candidates for various applications attributed to their high luminescent efficiency,moderate excited states lifetimes,stable chemical structure and tunable emission wavelength.2-Phenylquinoline（HPQ）is an important cyclometalated ligand.Currently,the emission of iridium（Ⅲ）complexes based on HPQ are mainly located in the orange-red range.This thesis will be focused on the effective tuning of excited states of HPQ-based iridium（Ⅲ）complexes（solution and solid states）and their potential applications in photoelectric devices,bioimaging and sensing.The main contents are described as follows:（1）A more facile method was developed to prepare bothβ-diketonate-based and triazolpyridine-based neutral iridium（Ⅲ）complexes.The corresponding chloro-bridged dimers together with 2.2 equiv ofβ-diketonate or triazolpyridine were stirred under very mild condition with dichloromethane as solvent and anhydrous potassium carbonate as deacid reagent at room temperature（²5°C）.The complexes obtained by this method are easy to be purified with high yields.（2）Fluorine atoms/trifluoromethyl group have been introduced into the different positions of ligand,and the effects on the photophysical properties of iridium（Ⅲ）complexes have been investigated in detail.All complexes display bright greenish-yellow/yellow emission with broad full width at half maximum（FWHM）over 100 nm and the increased absolute quantum efficiency(Φ_PL)（up to 0.92）in solution.Furthermore,high-performance yellow and complementary-color-based white OLEDs have been fabricated.The FWHMs of the yellow,greenish-yellow OLEDs are over 100 nm.The maximum external quantum efficiency of monochrome OLEDs can reach 24.1%.The CRI of blue and complementary yellow-based white OLED is as high as 78.（3）Basedonthepreviousresults,2-（4-fluoro-3-（trifluoromethyl）phenyl）-4-methylquinoline（HMePQ-3CF₃-4F）is employed as the cyclometalated ligand to design and synthesis neutral yellow-emitting iridium（Ⅲ）complexes with different ancillary ligands.The alternation of ancillary ligands is intended to finely tune the photophysical properties of yellow complexes.These neutral iridium（Ⅲ）complexes show bright greenish-yellow emission with the wavelength at the narrow range of540-563 nm and broad FWHM in the range of 96-103 nm,and the absoluteΦ_PLL of 0.75 to 0.95 in CH₂Cl₂.The unique feature of these novel complexes is the tunable dual emission from the solid states.One is attributed to intrinsic emission similar to emission in solution,another one with much lower emission energies is probably resulted from the weak interactions between the adjacent complexes.The solid state emission not only shows intensive greenish-yellow emission band,but also covers the far red,even the near-infrared region owing to the ultra-broad emission band,which will be of great importance for high-quality solid state lighting.（4）Two series of neutral heteroleptic iridium（Ⅲ）complexes have been designed and synthesized by varing the position of methoxyl group on the metalated phenyl ring including of ortho（o）-/meta（m）-/para（p）-positions to demonstrate the universality of position-induced tuning emission wavelength of iridium（Ⅲ）complexes.In both series of complexes,methoxyl group with electron-donating ability can evidently tune emission wavelengths of lepidine-based iridium（Ⅲ）complexes.The emission wavelength is quite different from the complex isomers of methoxyl group at m-position and at p-position.The emission wavelength of iridium（Ⅲ）complexes with methoxyl group at m-position is over 60 nm red-shift than that of complexes with methoxyl group at p-position.Especially,the emission of complex with the methoxyl group at m-position reaches the deep-red region with the peaks at 642nm in CH₂Cl₂,and 654 nm（Φ_p=0.4,Φ_s=0.61,highly sensitive to O₂）in dimethyl sulfoxide,indicating that the great potential as oxygen sensor for hypoxia imaging and PDT in cancer cells.Finally,oxygen-sensitive complex with deep-red emission and long emission lifetime was successfully employed to investigate both intracellular O₂ detection and image-guided PDT for cancer cells.