Synthesis, Structure, Photophysical And Electrophosphorescent Properties Of Irdium(Ⅲ) And Platinum(Ⅱ) Complexes Based On4-Methylquinoline Derivatives

Heavy-metal complexes that possess a unique d6, d8, and d10electron configuration show strong spin-orbit coupling, leading to efficient intersystem crossing from the singlet excited state to the triplet manifold. This strong spin-orbit coupling resuits in highly intense phosphorescent emission. The excited state properties of heavy-metal complexes mentioned above are very complicated. The rich excited state properties of heavy-metal complexes have attracted increasing interest.The emission colour of iridium(Ⅲ) and platinum(II) complexes that show strong phosphorescent emission can be determined by the combination of cyclometallating and ancillary ligands coordinated to the Ir(Ⅲ) or Pt(Ⅱ) core. The introduction of electron-withdrawing or electron-donating groups on the cyclometallating ligands enabled the adjustment of the electro-optical properties of the complexes. The most commonly used conditions are often rather harsh. The high boiling-point2-ethoxyethanol used in the process of general synthetic route is toxic, and what’s more, intermediate complexes have a potential risk of oxidation process or thermal decomposition, especially for compounds (especially for β-diketonates) containing sensitive functional groups at such high temperatures used in the reactions. Two series of novel neutral iridium(Ⅲ) complexes and platinum(Ⅱ) complexes have been designed and synthesised.(1) Five4-methyl-quinoline derivatives featuring different substitutent aromatic in2-position of quinoline,4-methyl-2-phenylquinoline,2-(2,4-difluorophenyl)-4-methylquinoline,2-(4-fluorophenyl)-4-methylquinoline,2-(4-methoxyphenyl)-4-methylqui-noline,4-methyl-2-(thiophen-2-yl)quinoline, have been synthesized. The iridium(Ⅲ) complexes [Ir(4m2pq)2(acac)(1), Ir(4m224Fpq)2(acac)(2), Ir(4m24Fpq)2(acac)(3), Ir(4m24mopq)2(acac)(4), Ir(4m2thq)2(acac)(5)] and platinum(Ⅱ) complexes [Pt(4m2pq)(acac)(6), Pt(4m224Fpq)(acac)(7), Pt(4m24Fpq)(acac)(8), Pt(4m24mopq)(acac)(9), Pt(4m2thq)(acac)(10)] have been synthesized based on five4-methyl-quinoline derivatives.1H NMR and13C{1H} NMR were employed for determining the chemical structures. Single-crystal X-ray diffraction spectra of selected complexes were also studied;(2) A mild condition, dichloromethane (CH2C12) as sovlent and anhydrous potassium carbonate (K2CO3) as deacid reagent at room temperature (25℃), was adopted for synthesizing β-diketonates based iridium(Ⅲ) complexes by the reaction of [(4m2pq)2Ir(μ-Cl)2Ir(4m2pq)2] and pentane-2,4-dione, such mild reaction conditions have proved to work out. That is a promising approach for the synthesis of β-diketonates based iridium(Ⅲ) complexes containing sensitive functional groups;(3) UV-visible absorption spectra, photoluminescence spectra were employed for studying the photophysical properties of two series of novel neutral iridium(Ⅲ) complexes and platinum(Ⅱ) complexes. The emission wavelength of Ir(C(?)N)2(acac) in solution of CH2C12can be tuned from 574to615nm (covering greenish-yellow, yellow, orange, red) by introducing different substitutent groups, and all the emission peak of Ir(C(?)N)2(acac) in solid state show a red shift of about20nm except for Ir(4m2thq)2(acac)(5) which is up to40nm. Highly intense phosphorescent emit form all five platinum(II) complexes in solid state with fine structures in spectra, What differs form the corresponding iridium(III) complexes is that the emission peak of Pt(C(?)N)(acac) in solid state is much blue shift compared with that of Pt(C(?)N)(acac) in solution of CH2Cl2. The details of emission of Pt(C(?)N)(acac) in solid state is that Pt(4m2pq)(acac)(6) emits at549nm,589nm,636nm, Pt(4m224Fpq)(acac)(7) emits at549nm,589nm,604nm, Pt(4m24Fpq)(acac)(8) emits at539nm,585nm,636nm, Pt(4m24mopq)(acac)(9) emits at533nm,577nm,624nm, and Pt(4m2thq)(acac)(10) emits at587nm,640nm,705nm;(4) The electroluminescent device of the configurations ITO/NPB (40nm)/CBP-doped Ir(Ⅲ) complex(6wt%and8wt%)(30nm)/BCP (10nm)/Alq3(30nm)/LiF (1nm)/Al for Ir complexes was fabricated. The EL spectra of devices based on Ir(C(?)N)2(acac) almost coincide with the PL spectra of Ir(C(?)N)2(acac) in solution of CH2Cl2and have no much changes at different applied voltages. The maximum brightness of devices based on [Ir(4m2pq)2(acac)(1), Ir(4m224Fpq)2(acac)(2), Ir(4m24Fpq)2(acac)(3) are above23000cd/m, and the corresponding current efficiencies are10.4cd/A,14.2cd/A,25.7cd/A, power efficiencies are5.0lm/W,8.1lm/W,15.7lm/W, respectively. What’s more, turn-on voltages are at3V. The electroluminescent device of the configurations ITO/NPB (40nm)/CBP-doped Pt(Ⅱ) complex(6wt%and8wt%)(20nm)/BCP (10nm)/Alq3(20nm)/LiF (1nm)/Al for Pt complexes was also fabricated. The performance of the device based on Pt(4m2pq)(acac)(6) is excellent. This devices shows orange-red emission at a maximum wavelength of596nm with a maximum brightness of23962cd/m2and corresponds to a current efficiency of16.3cd/A, power efficiency of8.1lm/W. Especially, the EL emission of the device based on Pt(4m24Fpq)(acac)(8) strongly depends on the doping concentration, it shows pure red emission at much higher doping concentration;(5) The phenomenon that chemical shifts of some protons at the specific positions of Ir(C(?)N)2(acac) and Pt(C(?)N)(acac) strongly depend on molecular spatial structures was investgated, and a reasonable interpretation proposed by us is that the chemical bond formed between cyclometallating ligands and Ir(Ⅲ) or Pt(Ⅱ) ion and spatial structures of complexes (diamagnetic effect of aromatic rings) codetermine the chemical shifts, especially, the later factor is dominant.